Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 5014 insertions, 0 deletions

diff --git a/mm/memory.c b/mm/memory.c
new file mode 100644
index 000000000..800834cff
--- /dev/null
+++ b/mm/memory.c
@@ -0,0 +1,5014 @@
+/*
+ *  linux/mm/memory.c
+ *
+ *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
+ */
+
+/*
+ * demand-loading started 01.12.91 - seems it is high on the list of
+ * things wanted, and it should be easy to implement. - Linus
+ */
+
+/*
+ * Ok, demand-loading was easy, shared pages a little bit tricker. Shared
+ * pages started 02.12.91, seems to work. - Linus.
+ *
+ * Tested sharing by executing about 30 /bin/sh: under the old kernel it
+ * would have taken more than the 6M I have free, but it worked well as
+ * far as I could see.
+ *
+ * Also corrected some "invalidate()"s - I wasn't doing enough of them.
+ */
+
+/*
+ * Real VM (paging to/from disk) started 18.12.91. Much more work and
+ * thought has to go into this. Oh, well..
+ * 19.12.91  -  works, somewhat. Sometimes I get faults, don't know why.
+ *		Found it. Everything seems to work now.
+ * 20.12.91  -  Ok, making the swap-device changeable like the root.
+ */
+
+/*
+ * 05.04.94  -  Multi-page memory management added for v1.1.
+ *              Idea by Alex Bligh (alex@cconcepts.co.uk)
+ *
+ * 16.07.99  -  Support of BIGMEM added by Gerhard Wichert, Siemens AG
+ *		(Gerhard.Wichert@pdb.siemens.de)
+ *
+ * Aug/Sep 2004 Changed to four level page tables (Andi Kleen)
+ */
+
+#include <linux/kernel_stat.h>
+#include <linux/mm.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/coredump.h>
+#include <linux/sched/numa_balancing.h>
+#include <linux/sched/task.h>
+#include <linux/hugetlb.h>
+#include <linux/mman.h>
+#include <linux/swap.h>
+#include <linux/highmem.h>
+#include <linux/pagemap.h>
+#include <linux/memremap.h>
+#include <linux/ksm.h>
+#include <linux/rmap.h>
+#include <linux/export.h>
+#include <linux/delayacct.h>
+#include <linux/init.h>
+#include <linux/pfn_t.h>
+#include <linux/writeback.h>
+#include <linux/memcontrol.h>
+#include <linux/mmu_notifier.h>
+#include <linux/swapops.h>
+#include <linux/elf.h>
+#include <linux/gfp.h>
+#include <linux/migrate.h>
+#include <linux/string.h>
+#include <linux/dma-debug.h>
+#include <linux/debugfs.h>
+#include <linux/userfaultfd_k.h>
+#include <linux/dax.h>
+#include <linux/oom.h>
+
+#include <asm/io.h>
+#include <asm/mmu_context.h>
+#include <asm/pgalloc.h>
+#include <linux/uaccess.h>
+#include <asm/tlb.h>
+#include <asm/tlbflush.h>
+#include <asm/pgtable.h>
+
+#include "internal.h"
+
+#if defined(LAST_CPUPID_NOT_IN_PAGE_FLAGS) && !defined(CONFIG_COMPILE_TEST)
+#warning Unfortunate NUMA and NUMA Balancing config, growing page-frame for last_cpupid.
+#endif
+
+#ifndef CONFIG_NEED_MULTIPLE_NODES
+/* use the per-pgdat data instead for discontigmem - mbligh */
+unsigned long max_mapnr;
+EXPORT_SYMBOL(max_mapnr);
+
+struct page *mem_map;
+EXPORT_SYMBOL(mem_map);
+#endif
+
+/*
+ * A number of key systems in x86 including ioremap() rely on the assumption
+ * that high_memory defines the upper bound on direct map memory, then end
+ * of ZONE_NORMAL.  Under CONFIG_DISCONTIG this means that max_low_pfn and
+ * highstart_pfn must be the same; there must be no gap between ZONE_NORMAL
+ * and ZONE_HIGHMEM.
+ */
+void *high_memory;
+EXPORT_SYMBOL(high_memory);
+
+/*
+ * Randomize the address space (stacks, mmaps, brk, etc.).
+ *
+ * ( When CONFIG_COMPAT_BRK=y we exclude brk from randomization,
+ *   as ancient (libc5 based) binaries can segfault. )
+ */
+int randomize_va_space __read_mostly =
+#ifdef CONFIG_COMPAT_BRK
+					1;
+#else
+					2;
+#endif
+
+#ifndef arch_faults_on_old_pte
+static inline bool arch_faults_on_old_pte(void)
+{
+	/*
+	 * Those arches which don't have hw access flag feature need to
+	 * implement their own helper. By default, "true" means pagefault
+	 * will be hit on old pte.
+	 */
+	return true;
+}
+#endif
+
+static int __init disable_randmaps(char *s)
+{
+	randomize_va_space = 0;
+	return 1;
+}
+__setup("norandmaps", disable_randmaps);
+
+unsigned long zero_pfn __read_mostly;
+EXPORT_SYMBOL(zero_pfn);
+
+unsigned long highest_memmap_pfn __read_mostly;
+
+/*
+ * CONFIG_MMU architectures set up ZERO_PAGE in their paging_init()
+ */
+static int __init init_zero_pfn(void)
+{
+	zero_pfn = page_to_pfn(ZERO_PAGE(0));
+	return 0;
+}
+early_initcall(init_zero_pfn);
+
+
+#if defined(SPLIT_RSS_COUNTING)
+
+void sync_mm_rss(struct mm_struct *mm)
+{
+	int i;
+
+	for (i = 0; i < NR_MM_COUNTERS; i++) {
+		if (current->rss_stat.count[i]) {
+			add_mm_counter(mm, i, current->rss_stat.count[i]);
+			current->rss_stat.count[i] = 0;
+		}
+	}
+	current->rss_stat.events = 0;
+}
+
+static void add_mm_counter_fast(struct mm_struct *mm, int member, int val)
+{
+	struct task_struct *task = current;
+
+	if (likely(task->mm == mm))
+		task->rss_stat.count[member] += val;
+	else
+		add_mm_counter(mm, member, val);
+}
+#define inc_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member, 1)
+#define dec_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member, -1)
+
+/* sync counter once per 64 page faults */
+#define TASK_RSS_EVENTS_THRESH	(64)
+static void check_sync_rss_stat(struct task_struct *task)
+{
+	if (unlikely(task != current))
+		return;
+	if (unlikely(task->rss_stat.events++ > TASK_RSS_EVENTS_THRESH))
+		sync_mm_rss(task->mm);
+}
+#else /* SPLIT_RSS_COUNTING */
+
+#define inc_mm_counter_fast(mm, member) inc_mm_counter(mm, member)
+#define dec_mm_counter_fast(mm, member) dec_mm_counter(mm, member)
+
+static void check_sync_rss_stat(struct task_struct *task)
+{
+}
+
+#endif /* SPLIT_RSS_COUNTING */
+
+#ifdef HAVE_GENERIC_MMU_GATHER
+
+static bool tlb_next_batch(struct mmu_gather *tlb)
+{
+	struct mmu_gather_batch *batch;
+
+	batch = tlb->active;
+	if (batch->next) {
+		tlb->active = batch->next;
+		return true;
+	}
+
+	if (tlb->batch_count == MAX_GATHER_BATCH_COUNT)
+		return false;
+
+	batch = (void *)__get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0);
+	if (!batch)
+		return false;
+
+	tlb->batch_count++;
+	batch->next = NULL;
+	batch->nr   = 0;
+	batch->max  = MAX_GATHER_BATCH;
+
+	tlb->active->next = batch;
+	tlb->active = batch;
+
+	return true;
+}
+
+void arch_tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
+				unsigned long start, unsigned long end)
+{
+	tlb->mm = mm;
+
+	/* Is it from 0 to ~0? */
+	tlb->fullmm     = !(start | (end+1));
+	tlb->need_flush_all = 0;
+	tlb->local.next = NULL;
+	tlb->local.nr   = 0;
+	tlb->local.max  = ARRAY_SIZE(tlb->__pages);
+	tlb->active     = &tlb->local;
+	tlb->batch_count = 0;
+
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+	tlb->batch = NULL;
+#endif
+	tlb->page_size = 0;
+
+	__tlb_reset_range(tlb);
+}
+
+static void tlb_flush_mmu_free(struct mmu_gather *tlb)
+{
+	struct mmu_gather_batch *batch;
+
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+	tlb_table_flush(tlb);
+#endif
+	for (batch = &tlb->local; batch && batch->nr; batch = batch->next) {
+		free_pages_and_swap_cache(batch->pages, batch->nr);
+		batch->nr = 0;
+	}
+	tlb->active = &tlb->local;
+}
+
+void tlb_flush_mmu(struct mmu_gather *tlb)
+{
+	tlb_flush_mmu_tlbonly(tlb);
+	tlb_flush_mmu_free(tlb);
+}
+
+/* tlb_finish_mmu
+ *	Called at the end of the shootdown operation to free up any resources
+ *	that were required.
+ */
+void arch_tlb_finish_mmu(struct mmu_gather *tlb,
+		unsigned long start, unsigned long end, bool force)
+{
+	struct mmu_gather_batch *batch, *next;
+
+	if (force)
+		__tlb_adjust_range(tlb, start, end - start);
+
+	tlb_flush_mmu(tlb);
+
+	/* keep the page table cache within bounds */
+	check_pgt_cache();
+
+	for (batch = tlb->local.next; batch; batch = next) {
+		next = batch->next;
+		free_pages((unsigned long)batch, 0);
+	}
+	tlb->local.next = NULL;
+}
+
+/* __tlb_remove_page
+ *	Must perform the equivalent to __free_pte(pte_get_and_clear(ptep)), while
+ *	handling the additional races in SMP caused by other CPUs caching valid
+ *	mappings in their TLBs. Returns the number of free page slots left.
+ *	When out of page slots we must call tlb_flush_mmu().
+ *returns true if the caller should flush.
+ */
+bool __tlb_remove_page_size(struct mmu_gather *tlb, struct page *page, int page_size)
+{
+	struct mmu_gather_batch *batch;
+
+	VM_BUG_ON(!tlb->end);
+	VM_WARN_ON(tlb->page_size != page_size);
+
+	batch = tlb->active;
+	/*
+	 * Add the page and check if we are full. If so
+	 * force a flush.
+	 */
+	batch->pages[batch->nr++] = page;
+	if (batch->nr == batch->max) {
+		if (!tlb_next_batch(tlb))
+			return true;
+		batch = tlb->active;
+	}
+	VM_BUG_ON_PAGE(batch->nr > batch->max, page);
+
+	return false;
+}
+
+void tlb_flush_pmd_range(struct mmu_gather *tlb, unsigned long address,
+			 unsigned long size)
+{
+	if (tlb->page_size != 0 && tlb->page_size != PMD_SIZE)
+		tlb_flush_mmu(tlb);
+
+	tlb->page_size = PMD_SIZE;
+	tlb->start = min(tlb->start, address);
+	tlb->end = max(tlb->end, address + size);
+}
+#endif /* HAVE_GENERIC_MMU_GATHER */
+
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+
+/*
+ * See the comment near struct mmu_table_batch.
+ */
+
+/*
+ * If we want tlb_remove_table() to imply TLB invalidates.
+ */
+static inline void tlb_table_invalidate(struct mmu_gather *tlb)
+{
+#ifdef CONFIG_HAVE_RCU_TABLE_INVALIDATE
+	/*
+	 * Invalidate page-table caches used by hardware walkers. Then we still
+	 * need to RCU-sched wait while freeing the pages because software
+	 * walkers can still be in-flight.
+	 */
+	tlb_flush_mmu_tlbonly(tlb);
+#endif
+}
+
+static void tlb_remove_table_smp_sync(void *arg)
+{
+	/* Simply deliver the interrupt */
+}
+
+static void tlb_remove_table_one(void *table)
+{
+	/*
+	 * This isn't an RCU grace period and hence the page-tables cannot be
+	 * assumed to be actually RCU-freed.
+	 *
+	 * It is however sufficient for software page-table walkers that rely on
+	 * IRQ disabling. See the comment near struct mmu_table_batch.
+	 */
+	smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
+	__tlb_remove_table(table);
+}
+
+static void tlb_remove_table_rcu(struct rcu_head *head)
+{
+	struct mmu_table_batch *batch;
+	int i;
+
+	batch = container_of(head, struct mmu_table_batch, rcu);
+
+	for (i = 0; i < batch->nr; i++)
+		__tlb_remove_table(batch->tables[i]);
+
+	free_page((unsigned long)batch);
+}
+
+void tlb_table_flush(struct mmu_gather *tlb)
+{
+	struct mmu_table_batch **batch = &tlb->batch;
+
+	if (*batch) {
+		tlb_table_invalidate(tlb);
+		call_rcu_sched(&(*batch)->rcu, tlb_remove_table_rcu);
+		*batch = NULL;
+	}
+}
+
+void tlb_remove_table(struct mmu_gather *tlb, void *table)
+{
+	struct mmu_table_batch **batch = &tlb->batch;
+
+	if (*batch == NULL) {
+		*batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
+		if (*batch == NULL) {
+			tlb_table_invalidate(tlb);
+			tlb_remove_table_one(table);
+			return;
+		}
+		(*batch)->nr = 0;
+	}
+
+	(*batch)->tables[(*batch)->nr++] = table;
+	if ((*batch)->nr == MAX_TABLE_BATCH)
+		tlb_table_flush(tlb);
+}
+
+#endif /* CONFIG_HAVE_RCU_TABLE_FREE */
+
+/**
+ * tlb_gather_mmu - initialize an mmu_gather structure for page-table tear-down
+ * @tlb: the mmu_gather structure to initialize
+ * @mm: the mm_struct of the target address space
+ * @start: start of the region that will be removed from the page-table
+ * @end: end of the region that will be removed from the page-table
+ *
+ * Called to initialize an (on-stack) mmu_gather structure for page-table
+ * tear-down from @mm. The @start and @end are set to 0 and -1
+ * respectively when @mm is without users and we're going to destroy
+ * the full address space (exit/execve).
+ */
+void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
+			unsigned long start, unsigned long end)
+{
+	arch_tlb_gather_mmu(tlb, mm, start, end);
+	inc_tlb_flush_pending(tlb->mm);
+}
+
+void tlb_finish_mmu(struct mmu_gather *tlb,
+		unsigned long start, unsigned long end)
+{
+	/*
+	 * If there are parallel threads are doing PTE changes on same range
+	 * under non-exclusive lock(e.g., mmap_sem read-side) but defer TLB
+	 * flush by batching, a thread has stable TLB entry can fail to flush
+	 * the TLB by observing pte_none|!pte_dirty, for example so flush TLB
+	 * forcefully if we detect parallel PTE batching threads.
+	 */
+	bool force = mm_tlb_flush_nested(tlb->mm);
+
+	arch_tlb_finish_mmu(tlb, start, end, force);
+	dec_tlb_flush_pending(tlb->mm);
+}
+
+/*
+ * Note: this doesn't free the actual pages themselves. That
+ * has been handled earlier when unmapping all the memory regions.
+ */
+static void free_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
+			   unsigned long addr)
+{
+	pgtable_t token = pmd_pgtable(*pmd);
+	pmd_clear(pmd);
+	pte_free_tlb(tlb, token, addr);
+	mm_dec_nr_ptes(tlb->mm);
+}
+
+static inline void free_pmd_range(struct mmu_gather *tlb, pud_t *pud,
+				unsigned long addr, unsigned long end,
+				unsigned long floor, unsigned long ceiling)
+{
+	pmd_t *pmd;
+	unsigned long next;
+	unsigned long start;
+
+	start = addr;
+	pmd = pmd_offset(pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if (pmd_none_or_clear_bad(pmd))
+			continue;
+		free_pte_range(tlb, pmd, addr);
+	} while (pmd++, addr = next, addr != end);
+
+	start &= PUD_MASK;
+	if (start < floor)
+		return;
+	if (ceiling) {
+		ceiling &= PUD_MASK;
+		if (!ceiling)
+			return;
+	}
+	if (end - 1 > ceiling - 1)
+		return;
+
+	pmd = pmd_offset(pud, start);
+	pud_clear(pud);
+	pmd_free_tlb(tlb, pmd, start);
+	mm_dec_nr_pmds(tlb->mm);
+}
+
+static inline void free_pud_range(struct mmu_gather *tlb, p4d_t *p4d,
+				unsigned long addr, unsigned long end,
+				unsigned long floor, unsigned long ceiling)
+{
+	pud_t *pud;
+	unsigned long next;
+	unsigned long start;
+
+	start = addr;
+	pud = pud_offset(p4d, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_none_or_clear_bad(pud))
+			continue;
+		free_pmd_range(tlb, pud, addr, next, floor, ceiling);
+	} while (pud++, addr = next, addr != end);
+
+	start &= P4D_MASK;
+	if (start < floor)
+		return;
+	if (ceiling) {
+		ceiling &= P4D_MASK;
+		if (!ceiling)
+			return;
+	}
+	if (end - 1 > ceiling - 1)
+		return;
+
+	pud = pud_offset(p4d, start);
+	p4d_clear(p4d);
+	pud_free_tlb(tlb, pud, start);
+	mm_dec_nr_puds(tlb->mm);
+}
+
+static inline void free_p4d_range(struct mmu_gather *tlb, pgd_t *pgd,
+				unsigned long addr, unsigned long end,
+				unsigned long floor, unsigned long ceiling)
+{
+	p4d_t *p4d;
+	unsigned long next;
+	unsigned long start;
+
+	start = addr;
+	p4d = p4d_offset(pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+		if (p4d_none_or_clear_bad(p4d))
+			continue;
+		free_pud_range(tlb, p4d, addr, next, floor, ceiling);
+	} while (p4d++, addr = next, addr != end);
+
+	start &= PGDIR_MASK;
+	if (start < floor)
+		return;
+	if (ceiling) {
+		ceiling &= PGDIR_MASK;
+		if (!ceiling)
+			return;
+	}
+	if (end - 1 > ceiling - 1)
+		return;
+
+	p4d = p4d_offset(pgd, start);
+	pgd_clear(pgd);
+	p4d_free_tlb(tlb, p4d, start);
+}
+
+/*
+ * This function frees user-level page tables of a process.
+ */
+void free_pgd_range(struct mmu_gather *tlb,
+			unsigned long addr, unsigned long end,
+			unsigned long floor, unsigned long ceiling)
+{
+	pgd_t *pgd;
+	unsigned long next;
+
+	/*
+	 * The next few lines have given us lots of grief...
+	 *
+	 * Why are we testing PMD* at this top level?  Because often
+	 * there will be no work to do at all, and we'd prefer not to
+	 * go all the way down to the bottom just to discover that.
+	 *
+	 * Why all these "- 1"s?  Because 0 represents both the bottom
+	 * of the address space and the top of it (using -1 for the
+	 * top wouldn't help much: the masks would do the wrong thing).
+	 * The rule is that addr 0 and floor 0 refer to the bottom of
+	 * the address space, but end 0 and ceiling 0 refer to the top
+	 * Comparisons need to use "end - 1" and "ceiling - 1" (though
+	 * that end 0 case should be mythical).
+	 *
+	 * Wherever addr is brought up or ceiling brought down, we must
+	 * be careful to reject "the opposite 0" before it confuses the
+	 * subsequent tests.  But what about where end is brought down
+	 * by PMD_SIZE below? no, end can't go down to 0 there.
+	 *
+	 * Whereas we round start (addr) and ceiling down, by different
+	 * masks at different levels, in order to test whether a table
+	 * now has no other vmas using it, so can be freed, we don't
+	 * bother to round floor or end up - the tests don't need that.
+	 */
+
+	addr &= PMD_MASK;
+	if (addr < floor) {
+		addr += PMD_SIZE;
+		if (!addr)
+			return;
+	}
+	if (ceiling) {
+		ceiling &= PMD_MASK;
+		if (!ceiling)
+			return;
+	}
+	if (end - 1 > ceiling - 1)
+		end -= PMD_SIZE;
+	if (addr > end - 1)
+		return;
+	/*
+	 * We add page table cache pages with PAGE_SIZE,
+	 * (see pte_free_tlb()), flush the tlb if we need
+	 */
+	tlb_remove_check_page_size_change(tlb, PAGE_SIZE);
+	pgd = pgd_offset(tlb->mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none_or_clear_bad(pgd))
+			continue;
+		free_p4d_range(tlb, pgd, addr, next, floor, ceiling);
+	} while (pgd++, addr = next, addr != end);
+}
+
+void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *vma,
+		unsigned long floor, unsigned long ceiling)
+{
+	while (vma) {
+		struct vm_area_struct *next = vma->vm_next;
+		unsigned long addr = vma->vm_start;
+
+		/*
+		 * Hide vma from rmap and truncate_pagecache before freeing
+		 * pgtables
+		 */
+		unlink_anon_vmas(vma);
+		unlink_file_vma(vma);
+
+		if (is_vm_hugetlb_page(vma)) {
+			hugetlb_free_pgd_range(tlb, addr, vma->vm_end,
+				floor, next ? next->vm_start : ceiling);
+		} else {
+			/*
+			 * Optimization: gather nearby vmas into one call down
+			 */
+			while (next && next->vm_start <= vma->vm_end + PMD_SIZE
+			       && !is_vm_hugetlb_page(next)) {
+				vma = next;
+				next = vma->vm_next;
+				unlink_anon_vmas(vma);
+				unlink_file_vma(vma);
+			}
+			free_pgd_range(tlb, addr, vma->vm_end,
+				floor, next ? next->vm_start : ceiling);
+		}
+		vma = next;
+	}
+}
+
+int __pte_alloc(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
+{
+	spinlock_t *ptl;
+	pgtable_t new = pte_alloc_one(mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	/*
+	 * Ensure all pte setup (eg. pte page lock and page clearing) are
+	 * visible before the pte is made visible to other CPUs by being
+	 * put into page tables.
+	 *
+	 * The other side of the story is the pointer chasing in the page
+	 * table walking code (when walking the page table without locking;
+	 * ie. most of the time). Fortunately, these data accesses consist
+	 * of a chain of data-dependent loads, meaning most CPUs (alpha
+	 * being the notable exception) will already guarantee loads are
+	 * seen in-order. See the alpha page table accessors for the
+	 * smp_read_barrier_depends() barriers in page table walking code.
+	 */
+	smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */
+
+	ptl = pmd_lock(mm, pmd);
+	if (likely(pmd_none(*pmd))) {	/* Has another populated it ? */
+		mm_inc_nr_ptes(mm);
+		pmd_populate(mm, pmd, new);
+		new = NULL;
+	}
+	spin_unlock(ptl);
+	if (new)
+		pte_free(mm, new);
+	return 0;
+}
+
+int __pte_alloc_kernel(pmd_t *pmd, unsigned long address)
+{
+	pte_t *new = pte_alloc_one_kernel(&init_mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	smp_wmb(); /* See comment in __pte_alloc */
+
+	spin_lock(&init_mm.page_table_lock);
+	if (likely(pmd_none(*pmd))) {	/* Has another populated it ? */
+		pmd_populate_kernel(&init_mm, pmd, new);
+		new = NULL;
+	}
+	spin_unlock(&init_mm.page_table_lock);
+	if (new)
+		pte_free_kernel(&init_mm, new);
+	return 0;
+}
+
+static inline void init_rss_vec(int *rss)
+{
+	memset(rss, 0, sizeof(int) * NR_MM_COUNTERS);
+}
+
+static inline void add_mm_rss_vec(struct mm_struct *mm, int *rss)
+{
+	int i;
+
+	if (current->mm == mm)
+		sync_mm_rss(mm);
+	for (i = 0; i < NR_MM_COUNTERS; i++)
+		if (rss[i])
+			add_mm_counter(mm, i, rss[i]);
+}
+
+/*
+ * This function is called to print an error when a bad pte
+ * is found. For example, we might have a PFN-mapped pte in
+ * a region that doesn't allow it.
+ *
+ * The calling function must still handle the error.
+ */
+static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
+			  pte_t pte, struct page *page)
+{
+	pgd_t *pgd = pgd_offset(vma->vm_mm, addr);
+	p4d_t *p4d = p4d_offset(pgd, addr);
+	pud_t *pud = pud_offset(p4d, addr);
+	pmd_t *pmd = pmd_offset(pud, addr);
+	struct address_space *mapping;
+	pgoff_t index;
+	static unsigned long resume;
+	static unsigned long nr_shown;
+	static unsigned long nr_unshown;
+
+	/*
+	 * Allow a burst of 60 reports, then keep quiet for that minute;
+	 * or allow a steady drip of one report per second.
+	 */
+	if (nr_shown == 60) {
+		if (time_before(jiffies, resume)) {
+			nr_unshown++;
+			return;
+		}
+		if (nr_unshown) {
+			pr_alert("BUG: Bad page map: %lu messages suppressed\n",
+				 nr_unshown);
+			nr_unshown = 0;
+		}
+		nr_shown = 0;
+	}
+	if (nr_shown++ == 0)
+		resume = jiffies + 60 * HZ;
+
+	mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
+	index = linear_page_index(vma, addr);
+
+	pr_alert("BUG: Bad page map in process %s  pte:%08llx pmd:%08llx\n",
+		 current->comm,
+		 (long long)pte_val(pte), (long long)pmd_val(*pmd));
+	if (page)
+		dump_page(page, "bad pte");
+	pr_alert("addr:%p vm_flags:%08lx anon_vma:%p mapping:%p index:%lx\n",
+		 (void *)addr, vma->vm_flags, vma->anon_vma, mapping, index);
+	pr_alert("file:%pD fault:%pf mmap:%pf readpage:%pf\n",
+		 vma->vm_file,
+		 vma->vm_ops ? vma->vm_ops->fault : NULL,
+		 vma->vm_file ? vma->vm_file->f_op->mmap : NULL,
+		 mapping ? mapping->a_ops->readpage : NULL);
+	dump_stack();
+	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
+}
+
+/*
+ * vm_normal_page -- This function gets the "struct page" associated with a pte.
+ *
+ * "Special" mappings do not wish to be associated with a "struct page" (either
+ * it doesn't exist, or it exists but they don't want to touch it). In this
+ * case, NULL is returned here. "Normal" mappings do have a struct page.
+ *
+ * There are 2 broad cases. Firstly, an architecture may define a pte_special()
+ * pte bit, in which case this function is trivial. Secondly, an architecture
+ * may not have a spare pte bit, which requires a more complicated scheme,
+ * described below.
+ *
+ * A raw VM_PFNMAP mapping (ie. one that is not COWed) is always considered a
+ * special mapping (even if there are underlying and valid "struct pages").
+ * COWed pages of a VM_PFNMAP are always normal.
+ *
+ * The way we recognize COWed pages within VM_PFNMAP mappings is through the
+ * rules set up by "remap_pfn_range()": the vma will have the VM_PFNMAP bit
+ * set, and the vm_pgoff will point to the first PFN mapped: thus every special
+ * mapping will always honor the rule
+ *
+ *	pfn_of_page == vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT)
+ *
+ * And for normal mappings this is false.
+ *
+ * This restricts such mappings to be a linear translation from virtual address
+ * to pfn. To get around this restriction, we allow arbitrary mappings so long
+ * as the vma is not a COW mapping; in that case, we know that all ptes are
+ * special (because none can have been COWed).
+ *
+ *
+ * In order to support COW of arbitrary special mappings, we have VM_MIXEDMAP.
+ *
+ * VM_MIXEDMAP mappings can likewise contain memory with or without "struct
+ * page" backing, however the difference is that _all_ pages with a struct
+ * page (that is, those where pfn_valid is true) are refcounted and considered
+ * normal pages by the VM. The disadvantage is that pages are refcounted
+ * (which can be slower and simply not an option for some PFNMAP users). The
+ * advantage is that we don't have to follow the strict linearity rule of
+ * PFNMAP mappings in order to support COWable mappings.
+ *
+ */
+struct page *_vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
+			     pte_t pte, bool with_public_device)
+{
+	unsigned long pfn = pte_pfn(pte);
+
+	if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {
+		if (likely(!pte_special(pte)))
+			goto check_pfn;
+		if (vma->vm_ops && vma->vm_ops->find_special_page)
+			return vma->vm_ops->find_special_page(vma, addr);
+		if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
+			return NULL;
+		if (is_zero_pfn(pfn))
+			return NULL;
+
+		/*
+		 * Device public pages are special pages (they are ZONE_DEVICE
+		 * pages but different from persistent memory). They behave
+		 * allmost like normal pages. The difference is that they are
+		 * not on the lru and thus should never be involve with any-
+		 * thing that involve lru manipulation (mlock, numa balancing,
+		 * ...).
+		 *
+		 * This is why we still want to return NULL for such page from
+		 * vm_normal_page() so that we do not have to special case all
+		 * call site of vm_normal_page().
+		 */
+		if (likely(pfn <= highest_memmap_pfn)) {
+			struct page *page = pfn_to_page(pfn);
+
+			if (is_device_public_page(page)) {
+				if (with_public_device)
+					return page;
+				return NULL;
+			}
+		}
+
+		if (pte_devmap(pte))
+			return NULL;
+
+		print_bad_pte(vma, addr, pte, NULL);
+		return NULL;
+	}
+
+	/* !CONFIG_ARCH_HAS_PTE_SPECIAL case follows: */
+
+	if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
+		if (vma->vm_flags & VM_MIXEDMAP) {
+			if (!pfn_valid(pfn))
+				return NULL;
+			goto out;
+		} else {
+			unsigned long off;
+			off = (addr - vma->vm_start) >> PAGE_SHIFT;
+			if (pfn == vma->vm_pgoff + off)
+				return NULL;
+			if (!is_cow_mapping(vma->vm_flags))
+				return NULL;
+		}
+	}
+
+	if (is_zero_pfn(pfn))
+		return NULL;
+
+check_pfn:
+	if (unlikely(pfn > highest_memmap_pfn)) {
+		print_bad_pte(vma, addr, pte, NULL);
+		return NULL;
+	}
+
+	/*
+	 * NOTE! We still have PageReserved() pages in the page tables.
+	 * eg. VDSO mappings can cause them to exist.
+	 */
+out:
+	return pfn_to_page(pfn);
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
+				pmd_t pmd)
+{
+	unsigned long pfn = pmd_pfn(pmd);
+
+	/*
+	 * There is no pmd_special() but there may be special pmds, e.g.
+	 * in a direct-access (dax) mapping, so let's just replicate the
+	 * !CONFIG_ARCH_HAS_PTE_SPECIAL case from vm_normal_page() here.
+	 */
+	if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
+		if (vma->vm_flags & VM_MIXEDMAP) {
+			if (!pfn_valid(pfn))
+				return NULL;
+			goto out;
+		} else {
+			unsigned long off;
+			off = (addr - vma->vm_start) >> PAGE_SHIFT;
+			if (pfn == vma->vm_pgoff + off)
+				return NULL;
+			if (!is_cow_mapping(vma->vm_flags))
+				return NULL;
+		}
+	}
+
+	if (pmd_devmap(pmd))
+		return NULL;
+	if (is_zero_pfn(pfn))
+		return NULL;
+	if (unlikely(pfn > highest_memmap_pfn))
+		return NULL;
+
+	/*
+	 * NOTE! We still have PageReserved() pages in the page tables.
+	 * eg. VDSO mappings can cause them to exist.
+	 */
+out:
+	return pfn_to_page(pfn);
+}
+#endif
+
+/*
+ * copy one vm_area from one task to the other. Assumes the page tables
+ * already present in the new task to be cleared in the whole range
+ * covered by this vma.
+ */
+
+static inline unsigned long
+copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		pte_t *dst_pte, pte_t *src_pte, struct vm_area_struct *vma,
+		unsigned long addr, int *rss)
+{
+	unsigned long vm_flags = vma->vm_flags;
+	pte_t pte = *src_pte;
+	struct page *page;
+
+	/* pte contains position in swap or file, so copy. */
+	if (unlikely(!pte_present(pte))) {
+		swp_entry_t entry = pte_to_swp_entry(pte);
+
+		if (likely(!non_swap_entry(entry))) {
+			if (swap_duplicate(entry) < 0)
+				return entry.val;
+
+			/* make sure dst_mm is on swapoff's mmlist. */
+			if (unlikely(list_empty(&dst_mm->mmlist))) {
+				spin_lock(&mmlist_lock);
+				if (list_empty(&dst_mm->mmlist))
+					list_add(&dst_mm->mmlist,
+							&src_mm->mmlist);
+				spin_unlock(&mmlist_lock);
+			}
+			rss[MM_SWAPENTS]++;
+		} else if (is_migration_entry(entry)) {
+			page = migration_entry_to_page(entry);
+
+			rss[mm_counter(page)]++;
+
+			if (is_write_migration_entry(entry) &&
+					is_cow_mapping(vm_flags)) {
+				/*
+				 * COW mappings require pages in both
+				 * parent and child to be set to read.
+				 */
+				make_migration_entry_read(&entry);
+				pte = swp_entry_to_pte(entry);
+				if (pte_swp_soft_dirty(*src_pte))
+					pte = pte_swp_mksoft_dirty(pte);
+				set_pte_at(src_mm, addr, src_pte, pte);
+			}
+		} else if (is_device_private_entry(entry)) {
+			page = device_private_entry_to_page(entry);
+
+			/*
+			 * Update rss count even for unaddressable pages, as
+			 * they should treated just like normal pages in this
+			 * respect.
+			 *
+			 * We will likely want to have some new rss counters
+			 * for unaddressable pages, at some point. But for now
+			 * keep things as they are.
+			 */
+			get_page(page);
+			rss[mm_counter(page)]++;
+			page_dup_rmap(page, false);
+
+			/*
+			 * We do not preserve soft-dirty information, because so
+			 * far, checkpoint/restore is the only feature that
+			 * requires that. And checkpoint/restore does not work
+			 * when a device driver is involved (you cannot easily
+			 * save and restore device driver state).
+			 */
+			if (is_write_device_private_entry(entry) &&
+			    is_cow_mapping(vm_flags)) {
+				make_device_private_entry_read(&entry);
+				pte = swp_entry_to_pte(entry);
+				set_pte_at(src_mm, addr, src_pte, pte);
+			}
+		}
+		goto out_set_pte;
+	}
+
+	/*
+	 * If it's a COW mapping, write protect it both
+	 * in the parent and the child
+	 */
+	if (is_cow_mapping(vm_flags) && pte_write(pte)) {
+		ptep_set_wrprotect(src_mm, addr, src_pte);
+		pte = pte_wrprotect(pte);
+	}
+
+	/*
+	 * If it's a shared mapping, mark it clean in
+	 * the child
+	 */
+	if (vm_flags & VM_SHARED)
+		pte = pte_mkclean(pte);
+	pte = pte_mkold(pte);
+
+	page = vm_normal_page(vma, addr, pte);
+	if (page) {
+		get_page(page);
+		page_dup_rmap(page, false);
+		rss[mm_counter(page)]++;
+	} else if (pte_devmap(pte)) {
+		page = pte_page(pte);
+
+		/*
+		 * Cache coherent device memory behave like regular page and
+		 * not like persistent memory page. For more informations see
+		 * MEMORY_DEVICE_CACHE_COHERENT in memory_hotplug.h
+		 */
+		if (is_device_public_page(page)) {
+			get_page(page);
+			page_dup_rmap(page, false);
+			rss[mm_counter(page)]++;
+		}
+	}
+
+out_set_pte:
+	set_pte_at(dst_mm, addr, dst_pte, pte);
+	return 0;
+}
+
+static int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		   pmd_t *dst_pmd, pmd_t *src_pmd, struct vm_area_struct *vma,
+		   unsigned long addr, unsigned long end)
+{
+	pte_t *orig_src_pte, *orig_dst_pte;
+	pte_t *src_pte, *dst_pte;
+	spinlock_t *src_ptl, *dst_ptl;
+	int progress = 0;
+	int rss[NR_MM_COUNTERS];
+	swp_entry_t entry = (swp_entry_t){0};
+
+again:
+	init_rss_vec(rss);
+
+	dst_pte = pte_alloc_map_lock(dst_mm, dst_pmd, addr, &dst_ptl);
+	if (!dst_pte)
+		return -ENOMEM;
+	src_pte = pte_offset_map(src_pmd, addr);
+	src_ptl = pte_lockptr(src_mm, src_pmd);
+	spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
+	orig_src_pte = src_pte;
+	orig_dst_pte = dst_pte;
+	arch_enter_lazy_mmu_mode();
+
+	do {
+		/*
+		 * We are holding two locks at this point - either of them
+		 * could generate latencies in another task on another CPU.
+		 */
+		if (progress >= 32) {
+			progress = 0;
+			if (need_resched() ||
+			    spin_needbreak(src_ptl) || spin_needbreak(dst_ptl))
+				break;
+		}
+		if (pte_none(*src_pte)) {
+			progress++;
+			continue;
+		}
+		entry.val = copy_one_pte(dst_mm, src_mm, dst_pte, src_pte,
+							vma, addr, rss);
+		if (entry.val)
+			break;
+		progress += 8;
+	} while (dst_pte++, src_pte++, addr += PAGE_SIZE, addr != end);
+
+	arch_leave_lazy_mmu_mode();
+	spin_unlock(src_ptl);
+	pte_unmap(orig_src_pte);
+	add_mm_rss_vec(dst_mm, rss);
+	pte_unmap_unlock(orig_dst_pte, dst_ptl);
+	cond_resched();
+
+	if (entry.val) {
+		if (add_swap_count_continuation(entry, GFP_KERNEL) < 0)
+			return -ENOMEM;
+		progress = 0;
+	}
+	if (addr != end)
+		goto again;
+	return 0;
+}
+
+static inline int copy_pmd_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		pud_t *dst_pud, pud_t *src_pud, struct vm_area_struct *vma,
+		unsigned long addr, unsigned long end)
+{
+	pmd_t *src_pmd, *dst_pmd;
+	unsigned long next;
+
+	dst_pmd = pmd_alloc(dst_mm, dst_pud, addr);
+	if (!dst_pmd)
+		return -ENOMEM;
+	src_pmd = pmd_offset(src_pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if (is_swap_pmd(*src_pmd) || pmd_trans_huge(*src_pmd)
+			|| pmd_devmap(*src_pmd)) {
+			int err;
+			VM_BUG_ON_VMA(next-addr != HPAGE_PMD_SIZE, vma);
+			err = copy_huge_pmd(dst_mm, src_mm,
+					    dst_pmd, src_pmd, addr, vma);
+			if (err == -ENOMEM)
+				return -ENOMEM;
+			if (!err)
+				continue;
+			/* fall through */
+		}
+		if (pmd_none_or_clear_bad(src_pmd))
+			continue;
+		if (copy_pte_range(dst_mm, src_mm, dst_pmd, src_pmd,
+						vma, addr, next))
+			return -ENOMEM;
+	} while (dst_pmd++, src_pmd++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int copy_pud_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		p4d_t *dst_p4d, p4d_t *src_p4d, struct vm_area_struct *vma,
+		unsigned long addr, unsigned long end)
+{
+	pud_t *src_pud, *dst_pud;
+	unsigned long next;
+
+	dst_pud = pud_alloc(dst_mm, dst_p4d, addr);
+	if (!dst_pud)
+		return -ENOMEM;
+	src_pud = pud_offset(src_p4d, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_trans_huge(*src_pud) || pud_devmap(*src_pud)) {
+			int err;
+
+			VM_BUG_ON_VMA(next-addr != HPAGE_PUD_SIZE, vma);
+			err = copy_huge_pud(dst_mm, src_mm,
+					    dst_pud, src_pud, addr, vma);
+			if (err == -ENOMEM)
+				return -ENOMEM;
+			if (!err)
+				continue;
+			/* fall through */
+		}
+		if (pud_none_or_clear_bad(src_pud))
+			continue;
+		if (copy_pmd_range(dst_mm, src_mm, dst_pud, src_pud,
+						vma, addr, next))
+			return -ENOMEM;
+	} while (dst_pud++, src_pud++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int copy_p4d_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		pgd_t *dst_pgd, pgd_t *src_pgd, struct vm_area_struct *vma,
+		unsigned long addr, unsigned long end)
+{
+	p4d_t *src_p4d, *dst_p4d;
+	unsigned long next;
+
+	dst_p4d = p4d_alloc(dst_mm, dst_pgd, addr);
+	if (!dst_p4d)
+		return -ENOMEM;
+	src_p4d = p4d_offset(src_pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+		if (p4d_none_or_clear_bad(src_p4d))
+			continue;
+		if (copy_pud_range(dst_mm, src_mm, dst_p4d, src_p4d,
+						vma, addr, next))
+			return -ENOMEM;
+	} while (dst_p4d++, src_p4d++, addr = next, addr != end);
+	return 0;
+}
+
+int copy_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
+		struct vm_area_struct *vma)
+{
+	pgd_t *src_pgd, *dst_pgd;
+	unsigned long next;
+	unsigned long addr = vma->vm_start;
+	unsigned long end = vma->vm_end;
+	unsigned long mmun_start;	/* For mmu_notifiers */
+	unsigned long mmun_end;		/* For mmu_notifiers */
+	bool is_cow;
+	int ret;
+
+	/*
+	 * Don't copy ptes where a page fault will fill them correctly.
+	 * Fork becomes much lighter when there are big shared or private
+	 * readonly mappings. The tradeoff is that copy_page_range is more
+	 * efficient than faulting.
+	 */
+	if (!(vma->vm_flags & (VM_HUGETLB | VM_PFNMAP | VM_MIXEDMAP)) &&
+			!vma->anon_vma)
+		return 0;
+
+	if (is_vm_hugetlb_page(vma))
+		return copy_hugetlb_page_range(dst_mm, src_mm, vma);
+
+	if (unlikely(vma->vm_flags & VM_PFNMAP)) {
+		/*
+		 * We do not free on error cases below as remove_vma
+		 * gets called on error from higher level routine
+		 */
+		ret = track_pfn_copy(vma);
+		if (ret)
+			return ret;
+	}
+
+	/*
+	 * We need to invalidate the secondary MMU mappings only when
+	 * there could be a permission downgrade on the ptes of the
+	 * parent mm. And a permission downgrade will only happen if
+	 * is_cow_mapping() returns true.
+	 */
+	is_cow = is_cow_mapping(vma->vm_flags);
+	mmun_start = addr;
+	mmun_end   = end;
+	if (is_cow)
+		mmu_notifier_invalidate_range_start(src_mm, mmun_start,
+						    mmun_end);
+
+	ret = 0;
+	dst_pgd = pgd_offset(dst_mm, addr);
+	src_pgd = pgd_offset(src_mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none_or_clear_bad(src_pgd))
+			continue;
+		if (unlikely(copy_p4d_range(dst_mm, src_mm, dst_pgd, src_pgd,
+					    vma, addr, next))) {
+			ret = -ENOMEM;
+			break;
+		}
+	} while (dst_pgd++, src_pgd++, addr = next, addr != end);
+
+	if (is_cow)
+		mmu_notifier_invalidate_range_end(src_mm, mmun_start, mmun_end);
+	return ret;
+}
+
+/* Whether we should zap all COWed (private) pages too */
+static inline bool should_zap_cows(struct zap_details *details)
+{
+	/* By default, zap all pages */
+	if (!details)
+		return true;
+
+	/* Or, we zap COWed pages only if the caller wants to */
+	return !details->check_mapping;
+}
+
+static unsigned long zap_pte_range(struct mmu_gather *tlb,
+				struct vm_area_struct *vma, pmd_t *pmd,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	struct mm_struct *mm = tlb->mm;
+	int force_flush = 0;
+	int rss[NR_MM_COUNTERS];
+	spinlock_t *ptl;
+	pte_t *start_pte;
+	pte_t *pte;
+	swp_entry_t entry;
+
+	tlb_remove_check_page_size_change(tlb, PAGE_SIZE);
+again:
+	init_rss_vec(rss);
+	start_pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+	pte = start_pte;
+	flush_tlb_batched_pending(mm);
+	arch_enter_lazy_mmu_mode();
+	do {
+		pte_t ptent = *pte;
+		if (pte_none(ptent))
+			continue;
+
+		if (pte_present(ptent)) {
+			struct page *page;
+
+			page = _vm_normal_page(vma, addr, ptent, true);
+			if (unlikely(details) && page) {
+				/*
+				 * unmap_shared_mapping_pages() wants to
+				 * invalidate cache without truncating:
+				 * unmap shared but keep private pages.
+				 */
+				if (details->check_mapping &&
+				    details->check_mapping != page_rmapping(page))
+					continue;
+			}
+			ptent = ptep_get_and_clear_full(mm, addr, pte,
+							tlb->fullmm);
+			tlb_remove_tlb_entry(tlb, pte, addr);
+			if (unlikely(!page))
+				continue;
+
+			if (!PageAnon(page)) {
+				if (pte_dirty(ptent)) {
+					force_flush = 1;
+					set_page_dirty(page);
+				}
+				if (pte_young(ptent) &&
+				    likely(!(vma->vm_flags & VM_SEQ_READ)))
+					mark_page_accessed(page);
+			}
+			rss[mm_counter(page)]--;
+			page_remove_rmap(page, false);
+			if (unlikely(page_mapcount(page) < 0))
+				print_bad_pte(vma, addr, ptent, page);
+			if (unlikely(__tlb_remove_page(tlb, page))) {
+				force_flush = 1;
+				addr += PAGE_SIZE;
+				break;
+			}
+			continue;
+		}
+
+		entry = pte_to_swp_entry(ptent);
+		if (non_swap_entry(entry) && is_device_private_entry(entry)) {
+			struct page *page = device_private_entry_to_page(entry);
+
+			if (unlikely(details && details->check_mapping)) {
+				/*
+				 * unmap_shared_mapping_pages() wants to
+				 * invalidate cache without truncating:
+				 * unmap shared but keep private pages.
+				 */
+				if (details->check_mapping !=
+				    page_rmapping(page))
+					continue;
+			}
+
+			pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
+			rss[mm_counter(page)]--;
+			page_remove_rmap(page, false);
+			put_page(page);
+			continue;
+		}
+
+		entry = pte_to_swp_entry(ptent);
+		if (!non_swap_entry(entry)) {
+			/* Genuine swap entry, hence a private anon page */
+			if (!should_zap_cows(details))
+				continue;
+			rss[MM_SWAPENTS]--;
+		} else if (is_migration_entry(entry)) {
+			struct page *page;
+
+			page = migration_entry_to_page(entry);
+			if (details && details->check_mapping &&
+			    details->check_mapping != page_rmapping(page))
+				continue;
+			rss[mm_counter(page)]--;
+		}
+		if (unlikely(!free_swap_and_cache(entry)))
+			print_bad_pte(vma, addr, ptent, NULL);
+		pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
+	} while (pte++, addr += PAGE_SIZE, addr != end);
+
+	add_mm_rss_vec(mm, rss);
+	arch_leave_lazy_mmu_mode();
+
+	/* Do the actual TLB flush before dropping ptl */
+	if (force_flush)
+		tlb_flush_mmu_tlbonly(tlb);
+	pte_unmap_unlock(start_pte, ptl);
+
+	/*
+	 * If we forced a TLB flush (either due to running out of
+	 * batch buffers or because we needed to flush dirty TLB
+	 * entries before releasing the ptl), free the batched
+	 * memory too. Restart if we didn't do everything.
+	 */
+	if (force_flush) {
+		force_flush = 0;
+		tlb_flush_mmu_free(tlb);
+		if (addr != end)
+			goto again;
+	}
+
+	return addr;
+}
+
+static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
+				struct vm_area_struct *vma, pud_t *pud,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	pmd_t *pmd;
+	unsigned long next;
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
+			if (next - addr != HPAGE_PMD_SIZE)
+				__split_huge_pmd(vma, pmd, addr, false, NULL);
+			else if (zap_huge_pmd(tlb, vma, pmd, addr))
+				goto next;
+			/* fall through */
+		} else if (details && details->single_page &&
+			   PageTransCompound(details->single_page) &&
+			   next - addr == HPAGE_PMD_SIZE && pmd_none(*pmd)) {
+			spinlock_t *ptl = pmd_lock(tlb->mm, pmd);
+			/*
+			 * Take and drop THP pmd lock so that we cannot return
+			 * prematurely, while zap_huge_pmd() has cleared *pmd,
+			 * but not yet decremented compound_mapcount().
+			 */
+			spin_unlock(ptl);
+		}
+
+		/*
+		 * Here there can be other concurrent MADV_DONTNEED or
+		 * trans huge page faults running, and if the pmd is
+		 * none or trans huge it can change under us. This is
+		 * because MADV_DONTNEED holds the mmap_sem in read
+		 * mode.
+		 */
+		if (pmd_none_or_trans_huge_or_clear_bad(pmd))
+			goto next;
+		next = zap_pte_range(tlb, vma, pmd, addr, next, details);
+next:
+		cond_resched();
+	} while (pmd++, addr = next, addr != end);
+
+	return addr;
+}
+
+static inline unsigned long zap_pud_range(struct mmu_gather *tlb,
+				struct vm_area_struct *vma, p4d_t *p4d,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	pud_t *pud;
+	unsigned long next;
+
+	pud = pud_offset(p4d, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_trans_huge(*pud) || pud_devmap(*pud)) {
+			if (next - addr != HPAGE_PUD_SIZE) {
+				VM_BUG_ON_VMA(!rwsem_is_locked(&tlb->mm->mmap_sem), vma);
+				split_huge_pud(vma, pud, addr);
+			} else if (zap_huge_pud(tlb, vma, pud, addr))
+				goto next;
+			/* fall through */
+		}
+		if (pud_none_or_clear_bad(pud))
+			continue;
+		next = zap_pmd_range(tlb, vma, pud, addr, next, details);
+next:
+		cond_resched();
+	} while (pud++, addr = next, addr != end);
+
+	return addr;
+}
+
+static inline unsigned long zap_p4d_range(struct mmu_gather *tlb,
+				struct vm_area_struct *vma, pgd_t *pgd,
+				unsigned long addr, unsigned long end,
+				struct zap_details *details)
+{
+	p4d_t *p4d;
+	unsigned long next;
+
+	p4d = p4d_offset(pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+		if (p4d_none_or_clear_bad(p4d))
+			continue;
+		next = zap_pud_range(tlb, vma, p4d, addr, next, details);
+	} while (p4d++, addr = next, addr != end);
+
+	return addr;
+}
+
+void unmap_page_range(struct mmu_gather *tlb,
+			     struct vm_area_struct *vma,
+			     unsigned long addr, unsigned long end,
+			     struct zap_details *details)
+{
+	pgd_t *pgd;
+	unsigned long next;
+
+	BUG_ON(addr >= end);
+	tlb_start_vma(tlb, vma);
+	pgd = pgd_offset(vma->vm_mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none_or_clear_bad(pgd))
+			continue;
+		next = zap_p4d_range(tlb, vma, pgd, addr, next, details);
+	} while (pgd++, addr = next, addr != end);
+	tlb_end_vma(tlb, vma);
+}
+
+
+static void unmap_single_vma(struct mmu_gather *tlb,
+		struct vm_area_struct *vma, unsigned long start_addr,
+		unsigned long end_addr,
+		struct zap_details *details)
+{
+	unsigned long start = max(vma->vm_start, start_addr);
+	unsigned long end;
+
+	if (start >= vma->vm_end)
+		return;
+	end = min(vma->vm_end, end_addr);
+	if (end <= vma->vm_start)
+		return;
+
+	if (vma->vm_file)
+		uprobe_munmap(vma, start, end);
+
+	if (unlikely(vma->vm_flags & VM_PFNMAP))
+		untrack_pfn(vma, 0, 0);
+
+	if (start != end) {
+		if (unlikely(is_vm_hugetlb_page(vma))) {
+			/*
+			 * It is undesirable to test vma->vm_file as it
+			 * should be non-null for valid hugetlb area.
+			 * However, vm_file will be NULL in the error
+			 * cleanup path of mmap_region. When
+			 * hugetlbfs ->mmap method fails,
+			 * mmap_region() nullifies vma->vm_file
+			 * before calling this function to clean up.
+			 * Since no pte has actually been setup, it is
+			 * safe to do nothing in this case.
+			 */
+			if (vma->vm_file) {
+				i_mmap_lock_write(vma->vm_file->f_mapping);
+				__unmap_hugepage_range_final(tlb, vma, start, end, NULL);
+				i_mmap_unlock_write(vma->vm_file->f_mapping);
+			}
+		} else
+			unmap_page_range(tlb, vma, start, end, details);
+	}
+}
+
+/**
+ * unmap_vmas - unmap a range of memory covered by a list of vma's
+ * @tlb: address of the caller's struct mmu_gather
+ * @vma: the starting vma
+ * @start_addr: virtual address at which to start unmapping
+ * @end_addr: virtual address at which to end unmapping
+ *
+ * Unmap all pages in the vma list.
+ *
+ * Only addresses between `start' and `end' will be unmapped.
+ *
+ * The VMA list must be sorted in ascending virtual address order.
+ *
+ * unmap_vmas() assumes that the caller will flush the whole unmapped address
+ * range after unmap_vmas() returns.  So the only responsibility here is to
+ * ensure that any thus-far unmapped pages are flushed before unmap_vmas()
+ * drops the lock and schedules.
+ */
+void unmap_vmas(struct mmu_gather *tlb,
+		struct vm_area_struct *vma, unsigned long start_addr,
+		unsigned long end_addr)
+{
+	struct mm_struct *mm = vma->vm_mm;
+
+	mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
+	for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next)
+		unmap_single_vma(tlb, vma, start_addr, end_addr, NULL);
+	mmu_notifier_invalidate_range_end(mm, start_addr, end_addr);
+}
+
+/**
+ * zap_page_range - remove user pages in a given range
+ * @vma: vm_area_struct holding the applicable pages
+ * @start: starting address of pages to zap
+ * @size: number of bytes to zap
+ *
+ * Caller must protect the VMA list
+ */
+void zap_page_range(struct vm_area_struct *vma, unsigned long start,
+		unsigned long size)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	struct mmu_gather tlb;
+	unsigned long end = start + size;
+
+	lru_add_drain();
+	tlb_gather_mmu(&tlb, mm, start, end);
+	update_hiwater_rss(mm);
+	mmu_notifier_invalidate_range_start(mm, start, end);
+	for ( ; vma && vma->vm_start < end; vma = vma->vm_next)
+		unmap_single_vma(&tlb, vma, start, end, NULL);
+	mmu_notifier_invalidate_range_end(mm, start, end);
+	tlb_finish_mmu(&tlb, start, end);
+}
+
+/**
+ * zap_page_range_single - remove user pages in a given range
+ * @vma: vm_area_struct holding the applicable pages
+ * @address: starting address of pages to zap
+ * @size: number of bytes to zap
+ * @details: details of shared cache invalidation
+ *
+ * The range must fit into one VMA.
+ */
+static void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
+		unsigned long size, struct zap_details *details)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	struct mmu_gather tlb;
+	unsigned long end = address + size;
+
+	lru_add_drain();
+	tlb_gather_mmu(&tlb, mm, address, end);
+	update_hiwater_rss(mm);
+	mmu_notifier_invalidate_range_start(mm, address, end);
+	unmap_single_vma(&tlb, vma, address, end, details);
+	mmu_notifier_invalidate_range_end(mm, address, end);
+	tlb_finish_mmu(&tlb, address, end);
+}
+
+/**
+ * zap_vma_ptes - remove ptes mapping the vma
+ * @vma: vm_area_struct holding ptes to be zapped
+ * @address: starting address of pages to zap
+ * @size: number of bytes to zap
+ *
+ * This function only unmaps ptes assigned to VM_PFNMAP vmas.
+ *
+ * The entire address range must be fully contained within the vma.
+ *
+ */
+void zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
+		unsigned long size)
+{
+	if (address < vma->vm_start || address + size > vma->vm_end ||
+	    		!(vma->vm_flags & VM_PFNMAP))
+		return;
+
+	zap_page_range_single(vma, address, size, NULL);
+}
+EXPORT_SYMBOL_GPL(zap_vma_ptes);
+
+pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
+			spinlock_t **ptl)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+
+	pgd = pgd_offset(mm, addr);
+	p4d = p4d_alloc(mm, pgd, addr);
+	if (!p4d)
+		return NULL;
+	pud = pud_alloc(mm, p4d, addr);
+	if (!pud)
+		return NULL;
+	pmd = pmd_alloc(mm, pud, addr);
+	if (!pmd)
+		return NULL;
+
+	VM_BUG_ON(pmd_trans_huge(*pmd));
+	return pte_alloc_map_lock(mm, pmd, addr, ptl);
+}
+
+/*
+ * This is the old fallback for page remapping.
+ *
+ * For historical reasons, it only allows reserved pages. Only
+ * old drivers should use this, and they needed to mark their
+ * pages reserved for the old functions anyway.
+ */
+static int insert_page(struct vm_area_struct *vma, unsigned long addr,
+			struct page *page, pgprot_t prot)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	int retval;
+	pte_t *pte;
+	spinlock_t *ptl;
+
+	retval = -EINVAL;
+	if (PageAnon(page))
+		goto out;
+	retval = -ENOMEM;
+	flush_dcache_page(page);
+	pte = get_locked_pte(mm, addr, &ptl);
+	if (!pte)
+		goto out;
+	retval = -EBUSY;
+	if (!pte_none(*pte))
+		goto out_unlock;
+
+	/* Ok, finally just insert the thing.. */
+	get_page(page);
+	inc_mm_counter_fast(mm, mm_counter_file(page));
+	page_add_file_rmap(page, false);
+	set_pte_at(mm, addr, pte, mk_pte(page, prot));
+
+	retval = 0;
+	pte_unmap_unlock(pte, ptl);
+	return retval;
+out_unlock:
+	pte_unmap_unlock(pte, ptl);
+out:
+	return retval;
+}
+
+/**
+ * vm_insert_page - insert single page into user vma
+ * @vma: user vma to map to
+ * @addr: target user address of this page
+ * @page: source kernel page
+ *
+ * This allows drivers to insert individual pages they've allocated
+ * into a user vma.
+ *
+ * The page has to be a nice clean _individual_ kernel allocation.
+ * If you allocate a compound page, you need to have marked it as
+ * such (__GFP_COMP), or manually just split the page up yourself
+ * (see split_page()).
+ *
+ * NOTE! Traditionally this was done with "remap_pfn_range()" which
+ * took an arbitrary page protection parameter. This doesn't allow
+ * that. Your vma protection will have to be set up correctly, which
+ * means that if you want a shared writable mapping, you'd better
+ * ask for a shared writable mapping!
+ *
+ * The page does not need to be reserved.
+ *
+ * Usually this function is called from f_op->mmap() handler
+ * under mm->mmap_sem write-lock, so it can change vma->vm_flags.
+ * Caller must set VM_MIXEDMAP on vma if it wants to call this
+ * function from other places, for example from page-fault handler.
+ */
+int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
+			struct page *page)
+{
+	if (addr < vma->vm_start || addr >= vma->vm_end)
+		return -EFAULT;
+	if (!page_count(page))
+		return -EINVAL;
+	if (!(vma->vm_flags & VM_MIXEDMAP)) {
+		BUG_ON(down_read_trylock(&vma->vm_mm->mmap_sem));
+		BUG_ON(vma->vm_flags & VM_PFNMAP);
+		vma->vm_flags |= VM_MIXEDMAP;
+	}
+	return insert_page(vma, addr, page, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(vm_insert_page);
+
+static int insert_pfn(struct vm_area_struct *vma, unsigned long addr,
+			pfn_t pfn, pgprot_t prot, bool mkwrite)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	int retval;
+	pte_t *pte, entry;
+	spinlock_t *ptl;
+
+	retval = -ENOMEM;
+	pte = get_locked_pte(mm, addr, &ptl);
+	if (!pte)
+		goto out;
+	retval = -EBUSY;
+	if (!pte_none(*pte)) {
+		if (mkwrite) {
+			/*
+			 * For read faults on private mappings the PFN passed
+			 * in may not match the PFN we have mapped if the
+			 * mapped PFN is a writeable COW page.  In the mkwrite
+			 * case we are creating a writable PTE for a shared
+			 * mapping and we expect the PFNs to match. If they
+			 * don't match, we are likely racing with block
+			 * allocation and mapping invalidation so just skip the
+			 * update.
+			 */
+			if (pte_pfn(*pte) != pfn_t_to_pfn(pfn)) {
+				WARN_ON_ONCE(!is_zero_pfn(pte_pfn(*pte)));
+				goto out_unlock;
+			}
+			entry = pte_mkyoung(*pte);
+			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+			if (ptep_set_access_flags(vma, addr, pte, entry, 1))
+				update_mmu_cache(vma, addr, pte);
+		}
+		goto out_unlock;
+	}
+
+	/* Ok, finally just insert the thing.. */
+	if (pfn_t_devmap(pfn))
+		entry = pte_mkdevmap(pfn_t_pte(pfn, prot));
+	else
+		entry = pte_mkspecial(pfn_t_pte(pfn, prot));
+
+	if (mkwrite) {
+		entry = pte_mkyoung(entry);
+		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+	}
+
+	set_pte_at(mm, addr, pte, entry);
+	update_mmu_cache(vma, addr, pte); /* XXX: why not for insert_page? */
+
+	retval = 0;
+out_unlock:
+	pte_unmap_unlock(pte, ptl);
+out:
+	return retval;
+}
+
+/**
+ * vm_insert_pfn - insert single pfn into user vma
+ * @vma: user vma to map to
+ * @addr: target user address of this page
+ * @pfn: source kernel pfn
+ *
+ * Similar to vm_insert_page, this allows drivers to insert individual pages
+ * they've allocated into a user vma. Same comments apply.
+ *
+ * This function should only be called from a vm_ops->fault handler, and
+ * in that case the handler should return NULL.
+ *
+ * vma cannot be a COW mapping.
+ *
+ * As this is called only for pages that do not currently exist, we
+ * do not need to flush old virtual caches or the TLB.
+ */
+int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
+			unsigned long pfn)
+{
+	return vm_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(vm_insert_pfn);
+
+/**
+ * vm_insert_pfn_prot - insert single pfn into user vma with specified pgprot
+ * @vma: user vma to map to
+ * @addr: target user address of this page
+ * @pfn: source kernel pfn
+ * @pgprot: pgprot flags for the inserted page
+ *
+ * This is exactly like vm_insert_pfn, except that it allows drivers to
+ * to override pgprot on a per-page basis.
+ *
+ * This only makes sense for IO mappings, and it makes no sense for
+ * cow mappings.  In general, using multiple vmas is preferable;
+ * vm_insert_pfn_prot should only be used if using multiple VMAs is
+ * impractical.
+ */
+int vm_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
+			unsigned long pfn, pgprot_t pgprot)
+{
+	int ret;
+	/*
+	 * Technically, architectures with pte_special can avoid all these
+	 * restrictions (same for remap_pfn_range).  However we would like
+	 * consistency in testing and feature parity among all, so we should
+	 * try to keep these invariants in place for everybody.
+	 */
+	BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
+	BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
+						(VM_PFNMAP|VM_MIXEDMAP));
+	BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
+	BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn));
+
+	if (addr < vma->vm_start || addr >= vma->vm_end)
+		return -EFAULT;
+
+	if (!pfn_modify_allowed(pfn, pgprot))
+		return -EACCES;
+
+	track_pfn_insert(vma, &pgprot, __pfn_to_pfn_t(pfn, PFN_DEV));
+
+	ret = insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot,
+			false);
+
+	return ret;
+}
+EXPORT_SYMBOL(vm_insert_pfn_prot);
+
+static bool vm_mixed_ok(struct vm_area_struct *vma, pfn_t pfn)
+{
+	/* these checks mirror the abort conditions in vm_normal_page */
+	if (vma->vm_flags & VM_MIXEDMAP)
+		return true;
+	if (pfn_t_devmap(pfn))
+		return true;
+	if (pfn_t_special(pfn))
+		return true;
+	if (is_zero_pfn(pfn_t_to_pfn(pfn)))
+		return true;
+	return false;
+}
+
+static int __vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
+			pfn_t pfn, bool mkwrite)
+{
+	pgprot_t pgprot = vma->vm_page_prot;
+
+	BUG_ON(!vm_mixed_ok(vma, pfn));
+
+	if (addr < vma->vm_start || addr >= vma->vm_end)
+		return -EFAULT;
+
+	track_pfn_insert(vma, &pgprot, pfn);
+
+	if (!pfn_modify_allowed(pfn_t_to_pfn(pfn), pgprot))
+		return -EACCES;
+
+	/*
+	 * If we don't have pte special, then we have to use the pfn_valid()
+	 * based VM_MIXEDMAP scheme (see vm_normal_page), and thus we *must*
+	 * refcount the page if pfn_valid is true (hence insert_page rather
+	 * than insert_pfn).  If a zero_pfn were inserted into a VM_MIXEDMAP
+	 * without pte special, it would there be refcounted as a normal page.
+	 */
+	if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) &&
+	    !pfn_t_devmap(pfn) && pfn_t_valid(pfn)) {
+		struct page *page;
+
+		/*
+		 * At this point we are committed to insert_page()
+		 * regardless of whether the caller specified flags that
+		 * result in pfn_t_has_page() == false.
+		 */
+		page = pfn_to_page(pfn_t_to_pfn(pfn));
+		return insert_page(vma, addr, page, pgprot);
+	}
+	return insert_pfn(vma, addr, pfn, pgprot, mkwrite);
+}
+
+int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
+			pfn_t pfn)
+{
+	return __vm_insert_mixed(vma, addr, pfn, false);
+
+}
+EXPORT_SYMBOL(vm_insert_mixed);
+
+/*
+ *  If the insertion of PTE failed because someone else already added a
+ *  different entry in the mean time, we treat that as success as we assume
+ *  the same entry was actually inserted.
+ */
+
+vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma,
+		unsigned long addr, pfn_t pfn)
+{
+	int err;
+
+	err =  __vm_insert_mixed(vma, addr, pfn, true);
+	if (err == -ENOMEM)
+		return VM_FAULT_OOM;
+	if (err < 0 && err != -EBUSY)
+		return VM_FAULT_SIGBUS;
+	return VM_FAULT_NOPAGE;
+}
+EXPORT_SYMBOL(vmf_insert_mixed_mkwrite);
+
+/*
+ * maps a range of physical memory into the requested pages. the old
+ * mappings are removed. any references to nonexistent pages results
+ * in null mappings (currently treated as "copy-on-access")
+ */
+static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,
+			unsigned long addr, unsigned long end,
+			unsigned long pfn, pgprot_t prot)
+{
+	pte_t *pte, *mapped_pte;
+	spinlock_t *ptl;
+	int err = 0;
+
+	mapped_pte = pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
+	if (!pte)
+		return -ENOMEM;
+	arch_enter_lazy_mmu_mode();
+	do {
+		BUG_ON(!pte_none(*pte));
+		if (!pfn_modify_allowed(pfn, prot)) {
+			err = -EACCES;
+			break;
+		}
+		set_pte_at(mm, addr, pte, pte_mkspecial(pfn_pte(pfn, prot)));
+		pfn++;
+	} while (pte++, addr += PAGE_SIZE, addr != end);
+	arch_leave_lazy_mmu_mode();
+	pte_unmap_unlock(mapped_pte, ptl);
+	return err;
+}
+
+static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud,
+			unsigned long addr, unsigned long end,
+			unsigned long pfn, pgprot_t prot)
+{
+	pmd_t *pmd;
+	unsigned long next;
+	int err;
+
+	pfn -= addr >> PAGE_SHIFT;
+	pmd = pmd_alloc(mm, pud, addr);
+	if (!pmd)
+		return -ENOMEM;
+	VM_BUG_ON(pmd_trans_huge(*pmd));
+	do {
+		next = pmd_addr_end(addr, end);
+		err = remap_pte_range(mm, pmd, addr, next,
+				pfn + (addr >> PAGE_SHIFT), prot);
+		if (err)
+			return err;
+	} while (pmd++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int remap_pud_range(struct mm_struct *mm, p4d_t *p4d,
+			unsigned long addr, unsigned long end,
+			unsigned long pfn, pgprot_t prot)
+{
+	pud_t *pud;
+	unsigned long next;
+	int err;
+
+	pfn -= addr >> PAGE_SHIFT;
+	pud = pud_alloc(mm, p4d, addr);
+	if (!pud)
+		return -ENOMEM;
+	do {
+		next = pud_addr_end(addr, end);
+		err = remap_pmd_range(mm, pud, addr, next,
+				pfn + (addr >> PAGE_SHIFT), prot);
+		if (err)
+			return err;
+	} while (pud++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int remap_p4d_range(struct mm_struct *mm, pgd_t *pgd,
+			unsigned long addr, unsigned long end,
+			unsigned long pfn, pgprot_t prot)
+{
+	p4d_t *p4d;
+	unsigned long next;
+	int err;
+
+	pfn -= addr >> PAGE_SHIFT;
+	p4d = p4d_alloc(mm, pgd, addr);
+	if (!p4d)
+		return -ENOMEM;
+	do {
+		next = p4d_addr_end(addr, end);
+		err = remap_pud_range(mm, p4d, addr, next,
+				pfn + (addr >> PAGE_SHIFT), prot);
+		if (err)
+			return err;
+	} while (p4d++, addr = next, addr != end);
+	return 0;
+}
+
+/**
+ * remap_pfn_range - remap kernel memory to userspace
+ * @vma: user vma to map to
+ * @addr: target user address to start at
+ * @pfn: physical address of kernel memory
+ * @size: size of map area
+ * @prot: page protection flags for this mapping
+ *
+ *  Note: this is only safe if the mm semaphore is held when called.
+ */
+int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
+		    unsigned long pfn, unsigned long size, pgprot_t prot)
+{
+	pgd_t *pgd;
+	unsigned long next;
+	unsigned long end = addr + PAGE_ALIGN(size);
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long remap_pfn = pfn;
+	int err;
+
+	/*
+	 * Physically remapped pages are special. Tell the
+	 * rest of the world about it:
+	 *   VM_IO tells people not to look at these pages
+	 *	(accesses can have side effects).
+	 *   VM_PFNMAP tells the core MM that the base pages are just
+	 *	raw PFN mappings, and do not have a "struct page" associated
+	 *	with them.
+	 *   VM_DONTEXPAND
+	 *      Disable vma merging and expanding with mremap().
+	 *   VM_DONTDUMP
+	 *      Omit vma from core dump, even when VM_IO turned off.
+	 *
+	 * There's a horrible special case to handle copy-on-write
+	 * behaviour that some programs depend on. We mark the "original"
+	 * un-COW'ed pages by matching them up with "vma->vm_pgoff".
+	 * See vm_normal_page() for details.
+	 */
+	if (is_cow_mapping(vma->vm_flags)) {
+		if (addr != vma->vm_start || end != vma->vm_end)
+			return -EINVAL;
+		vma->vm_pgoff = pfn;
+	}
+
+	err = track_pfn_remap(vma, &prot, remap_pfn, addr, PAGE_ALIGN(size));
+	if (err)
+		return -EINVAL;
+
+	vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
+
+	BUG_ON(addr >= end);
+	pfn -= addr >> PAGE_SHIFT;
+	pgd = pgd_offset(mm, addr);
+	flush_cache_range(vma, addr, end);
+	do {
+		next = pgd_addr_end(addr, end);
+		err = remap_p4d_range(mm, pgd, addr, next,
+				pfn + (addr >> PAGE_SHIFT), prot);
+		if (err)
+			break;
+	} while (pgd++, addr = next, addr != end);
+
+	if (err)
+		untrack_pfn(vma, remap_pfn, PAGE_ALIGN(size));
+
+	return err;
+}
+EXPORT_SYMBOL(remap_pfn_range);
+
+/**
+ * vm_iomap_memory - remap memory to userspace
+ * @vma: user vma to map to
+ * @start: start of area
+ * @len: size of area
+ *
+ * This is a simplified io_remap_pfn_range() for common driver use. The
+ * driver just needs to give us the physical memory range to be mapped,
+ * we'll figure out the rest from the vma information.
+ *
+ * NOTE! Some drivers might want to tweak vma->vm_page_prot first to get
+ * whatever write-combining details or similar.
+ */
+int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len)
+{
+	unsigned long vm_len, pfn, pages;
+
+	/* Check that the physical memory area passed in looks valid */
+	if (start + len < start)
+		return -EINVAL;
+	/*
+	 * You *really* shouldn't map things that aren't page-aligned,
+	 * but we've historically allowed it because IO memory might
+	 * just have smaller alignment.
+	 */
+	len += start & ~PAGE_MASK;
+	pfn = start >> PAGE_SHIFT;
+	pages = (len + ~PAGE_MASK) >> PAGE_SHIFT;
+	if (pfn + pages < pfn)
+		return -EINVAL;
+
+	/* We start the mapping 'vm_pgoff' pages into the area */
+	if (vma->vm_pgoff > pages)
+		return -EINVAL;
+	pfn += vma->vm_pgoff;
+	pages -= vma->vm_pgoff;
+
+	/* Can we fit all of the mapping? */
+	vm_len = vma->vm_end - vma->vm_start;
+	if (vm_len >> PAGE_SHIFT > pages)
+		return -EINVAL;
+
+	/* Ok, let it rip */
+	return io_remap_pfn_range(vma, vma->vm_start, pfn, vm_len, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(vm_iomap_memory);
+
+static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
+				     unsigned long addr, unsigned long end,
+				     pte_fn_t fn, void *data)
+{
+	pte_t *pte;
+	int err;
+	pgtable_t token;
+	spinlock_t *uninitialized_var(ptl);
+
+	pte = (mm == &init_mm) ?
+		pte_alloc_kernel(pmd, addr) :
+		pte_alloc_map_lock(mm, pmd, addr, &ptl);
+	if (!pte)
+		return -ENOMEM;
+
+	BUG_ON(pmd_huge(*pmd));
+
+	arch_enter_lazy_mmu_mode();
+
+	token = pmd_pgtable(*pmd);
+
+	do {
+		err = fn(pte++, token, addr, data);
+		if (err)
+			break;
+	} while (addr += PAGE_SIZE, addr != end);
+
+	arch_leave_lazy_mmu_mode();
+
+	if (mm != &init_mm)
+		pte_unmap_unlock(pte-1, ptl);
+	return err;
+}
+
+static int apply_to_pmd_range(struct mm_struct *mm, pud_t *pud,
+				     unsigned long addr, unsigned long end,
+				     pte_fn_t fn, void *data)
+{
+	pmd_t *pmd;
+	unsigned long next;
+	int err;
+
+	BUG_ON(pud_huge(*pud));
+
+	pmd = pmd_alloc(mm, pud, addr);
+	if (!pmd)
+		return -ENOMEM;
+	do {
+		next = pmd_addr_end(addr, end);
+		err = apply_to_pte_range(mm, pmd, addr, next, fn, data);
+		if (err)
+			break;
+	} while (pmd++, addr = next, addr != end);
+	return err;
+}
+
+static int apply_to_pud_range(struct mm_struct *mm, p4d_t *p4d,
+				     unsigned long addr, unsigned long end,
+				     pte_fn_t fn, void *data)
+{
+	pud_t *pud;
+	unsigned long next;
+	int err;
+
+	pud = pud_alloc(mm, p4d, addr);
+	if (!pud)
+		return -ENOMEM;
+	do {
+		next = pud_addr_end(addr, end);
+		err = apply_to_pmd_range(mm, pud, addr, next, fn, data);
+		if (err)
+			break;
+	} while (pud++, addr = next, addr != end);
+	return err;
+}
+
+static int apply_to_p4d_range(struct mm_struct *mm, pgd_t *pgd,
+				     unsigned long addr, unsigned long end,
+				     pte_fn_t fn, void *data)
+{
+	p4d_t *p4d;
+	unsigned long next;
+	int err;
+
+	p4d = p4d_alloc(mm, pgd, addr);
+	if (!p4d)
+		return -ENOMEM;
+	do {
+		next = p4d_addr_end(addr, end);
+		err = apply_to_pud_range(mm, p4d, addr, next, fn, data);
+		if (err)
+			break;
+	} while (p4d++, addr = next, addr != end);
+	return err;
+}
+
+/*
+ * Scan a region of virtual memory, filling in page tables as necessary
+ * and calling a provided function on each leaf page table.
+ */
+int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
+			unsigned long size, pte_fn_t fn, void *data)
+{
+	pgd_t *pgd;
+	unsigned long next;
+	unsigned long end = addr + size;
+	int err;
+
+	if (WARN_ON(addr >= end))
+		return -EINVAL;
+
+	pgd = pgd_offset(mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		err = apply_to_p4d_range(mm, pgd, addr, next, fn, data);
+		if (err)
+			break;
+	} while (pgd++, addr = next, addr != end);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(apply_to_page_range);
+
+/*
+ * handle_pte_fault chooses page fault handler according to an entry which was
+ * read non-atomically.  Before making any commitment, on those architectures
+ * or configurations (e.g. i386 with PAE) which might give a mix of unmatched
+ * parts, do_swap_page must check under lock before unmapping the pte and
+ * proceeding (but do_wp_page is only called after already making such a check;
+ * and do_anonymous_page can safely check later on).
+ */
+static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
+				pte_t *page_table, pte_t orig_pte)
+{
+	int same = 1;
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
+	if (sizeof(pte_t) > sizeof(unsigned long)) {
+		spinlock_t *ptl = pte_lockptr(mm, pmd);
+		spin_lock(ptl);
+		same = pte_same(*page_table, orig_pte);
+		spin_unlock(ptl);
+	}
+#endif
+	pte_unmap(page_table);
+	return same;
+}
+
+static inline bool cow_user_page(struct page *dst, struct page *src,
+				 struct vm_fault *vmf)
+{
+	bool ret;
+	void *kaddr;
+	void __user *uaddr;
+	bool locked = false;
+	struct vm_area_struct *vma = vmf->vma;
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long addr = vmf->address;
+
+	debug_dma_assert_idle(src);
+
+	if (likely(src)) {
+		copy_user_highpage(dst, src, addr, vma);
+		return true;
+	}
+
+	/*
+	 * If the source page was a PFN mapping, we don't have
+	 * a "struct page" for it. We do a best-effort copy by
+	 * just copying from the original user address. If that
+	 * fails, we just zero-fill it. Live with it.
+	 */
+	kaddr = kmap_atomic(dst);
+	uaddr = (void __user *)(addr & PAGE_MASK);
+
+	/*
+	 * On architectures with software "accessed" bits, we would
+	 * take a double page fault, so mark it accessed here.
+	 */
+	if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) {
+		pte_t entry;
+
+		vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
+		locked = true;
+		if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
+			/*
+			 * Other thread has already handled the fault
+			 * and we don't need to do anything. If it's
+			 * not the case, the fault will be triggered
+			 * again on the same address.
+			 */
+			ret = false;
+			goto pte_unlock;
+		}
+
+		entry = pte_mkyoung(vmf->orig_pte);
+		if (ptep_set_access_flags(vma, addr, vmf->pte, entry, 0))
+			update_mmu_cache(vma, addr, vmf->pte);
+	}
+
+	/*
+	 * This really shouldn't fail, because the page is there
+	 * in the page tables. But it might just be unreadable,
+	 * in which case we just give up and fill the result with
+	 * zeroes.
+	 */
+	if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
+		if (locked)
+			goto warn;
+
+		/* Re-validate under PTL if the page is still mapped */
+		vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
+		locked = true;
+		if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
+			/* The PTE changed under us. Retry page fault. */
+			ret = false;
+			goto pte_unlock;
+		}
+
+		/*
+		 * The same page can be mapped back since last copy attampt.
+		 * Try to copy again under PTL.
+		 */
+		if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
+			/*
+			 * Give a warn in case there can be some obscure
+			 * use-case
+			 */
+warn:
+			WARN_ON_ONCE(1);
+			clear_page(kaddr);
+		}
+	}
+
+	ret = true;
+
+pte_unlock:
+	if (locked)
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+	kunmap_atomic(kaddr);
+	flush_dcache_page(dst);
+
+	return ret;
+}
+
+static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma)
+{
+	struct file *vm_file = vma->vm_file;
+
+	if (vm_file)
+		return mapping_gfp_mask(vm_file->f_mapping) | __GFP_FS | __GFP_IO;
+
+	/*
+	 * Special mappings (e.g. VDSO) do not have any file so fake
+	 * a default GFP_KERNEL for them.
+	 */
+	return GFP_KERNEL;
+}
+
+/*
+ * Notify the address space that the page is about to become writable so that
+ * it can prohibit this or wait for the page to get into an appropriate state.
+ *
+ * We do this without the lock held, so that it can sleep if it needs to.
+ */
+static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
+{
+	vm_fault_t ret;
+	struct page *page = vmf->page;
+	unsigned int old_flags = vmf->flags;
+
+	vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
+
+	ret = vmf->vma->vm_ops->page_mkwrite(vmf);
+	/* Restore original flags so that caller is not surprised */
+	vmf->flags = old_flags;
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
+		return ret;
+	if (unlikely(!(ret & VM_FAULT_LOCKED))) {
+		lock_page(page);
+		if (!page->mapping) {
+			unlock_page(page);
+			return 0; /* retry */
+		}
+		ret |= VM_FAULT_LOCKED;
+	} else
+		VM_BUG_ON_PAGE(!PageLocked(page), page);
+	return ret;
+}
+
+/*
+ * Handle dirtying of a page in shared file mapping on a write fault.
+ *
+ * The function expects the page to be locked and unlocks it.
+ */
+static void fault_dirty_shared_page(struct vm_area_struct *vma,
+				    struct page *page)
+{
+	struct address_space *mapping;
+	bool dirtied;
+	bool page_mkwrite = vma->vm_ops && vma->vm_ops->page_mkwrite;
+
+	dirtied = set_page_dirty(page);
+	VM_BUG_ON_PAGE(PageAnon(page), page);
+	/*
+	 * Take a local copy of the address_space - page.mapping may be zeroed
+	 * by truncate after unlock_page().   The address_space itself remains
+	 * pinned by vma->vm_file's reference.  We rely on unlock_page()'s
+	 * release semantics to prevent the compiler from undoing this copying.
+	 */
+	mapping = page_rmapping(page);
+	unlock_page(page);
+
+	if ((dirtied || page_mkwrite) && mapping) {
+		/*
+		 * Some device drivers do not set page.mapping
+		 * but still dirty their pages
+		 */
+		balance_dirty_pages_ratelimited(mapping);
+	}
+
+	if (!page_mkwrite)
+		file_update_time(vma->vm_file);
+}
+
+/*
+ * Handle write page faults for pages that can be reused in the current vma
+ *
+ * This can happen either due to the mapping being with the VM_SHARED flag,
+ * or due to us being the last reference standing to the page. In either
+ * case, all we need to do here is to mark the page as writable and update
+ * any related book-keeping.
+ */
+static inline void wp_page_reuse(struct vm_fault *vmf)
+	__releases(vmf->ptl)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct page *page = vmf->page;
+	pte_t entry;
+	/*
+	 * Clear the pages cpupid information as the existing
+	 * information potentially belongs to a now completely
+	 * unrelated process.
+	 */
+	if (page)
+		page_cpupid_xchg_last(page, (1 << LAST_CPUPID_SHIFT) - 1);
+
+	flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
+	entry = pte_mkyoung(vmf->orig_pte);
+	entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+	if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
+		update_mmu_cache(vma, vmf->address, vmf->pte);
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+}
+
+/*
+ * Handle the case of a page which we actually need to copy to a new page.
+ *
+ * Called with mmap_sem locked and the old page referenced, but
+ * without the ptl held.
+ *
+ * High level logic flow:
+ *
+ * - Allocate a page, copy the content of the old page to the new one.
+ * - Handle book keeping and accounting - cgroups, mmu-notifiers, etc.
+ * - Take the PTL. If the pte changed, bail out and release the allocated page
+ * - If the pte is still the way we remember it, update the page table and all
+ *   relevant references. This includes dropping the reference the page-table
+ *   held to the old page, as well as updating the rmap.
+ * - In any case, unlock the PTL and drop the reference we took to the old page.
+ */
+static vm_fault_t wp_page_copy(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct mm_struct *mm = vma->vm_mm;
+	struct page *old_page = vmf->page;
+	struct page *new_page = NULL;
+	pte_t entry;
+	int page_copied = 0;
+	const unsigned long mmun_start = vmf->address & PAGE_MASK;
+	const unsigned long mmun_end = mmun_start + PAGE_SIZE;
+	struct mem_cgroup *memcg;
+
+	if (unlikely(anon_vma_prepare(vma)))
+		goto oom;
+
+	if (is_zero_pfn(pte_pfn(vmf->orig_pte))) {
+		new_page = alloc_zeroed_user_highpage_movable(vma,
+							      vmf->address);
+		if (!new_page)
+			goto oom;
+	} else {
+		new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma,
+				vmf->address);
+		if (!new_page)
+			goto oom;
+
+		if (!cow_user_page(new_page, old_page, vmf)) {
+			/*
+			 * COW failed, if the fault was solved by other,
+			 * it's fine. If not, userspace would re-fault on
+			 * the same address and we will handle the fault
+			 * from the second attempt.
+			 */
+			put_page(new_page);
+			if (old_page)
+				put_page(old_page);
+			return 0;
+		}
+	}
+
+	if (mem_cgroup_try_charge_delay(new_page, mm, GFP_KERNEL, &memcg, false))
+		goto oom_free_new;
+
+	__SetPageUptodate(new_page);
+
+	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+
+	/*
+	 * Re-check the pte - we dropped the lock
+	 */
+	vmf->pte = pte_offset_map_lock(mm, vmf->pmd, vmf->address, &vmf->ptl);
+	if (likely(pte_same(*vmf->pte, vmf->orig_pte))) {
+		if (old_page) {
+			if (!PageAnon(old_page)) {
+				dec_mm_counter_fast(mm,
+						mm_counter_file(old_page));
+				inc_mm_counter_fast(mm, MM_ANONPAGES);
+			}
+		} else {
+			inc_mm_counter_fast(mm, MM_ANONPAGES);
+		}
+		flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
+		entry = mk_pte(new_page, vma->vm_page_prot);
+		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+		/*
+		 * Clear the pte entry and flush it first, before updating the
+		 * pte with the new entry. This will avoid a race condition
+		 * seen in the presence of one thread doing SMC and another
+		 * thread doing COW.
+		 */
+		ptep_clear_flush_notify(vma, vmf->address, vmf->pte);
+		page_add_new_anon_rmap(new_page, vma, vmf->address, false);
+		mem_cgroup_commit_charge(new_page, memcg, false, false);
+		lru_cache_add_active_or_unevictable(new_page, vma);
+		/*
+		 * We call the notify macro here because, when using secondary
+		 * mmu page tables (such as kvm shadow page tables), we want the
+		 * new page to be mapped directly into the secondary page table.
+		 */
+		set_pte_at_notify(mm, vmf->address, vmf->pte, entry);
+		update_mmu_cache(vma, vmf->address, vmf->pte);
+		if (old_page) {
+			/*
+			 * Only after switching the pte to the new page may
+			 * we remove the mapcount here. Otherwise another
+			 * process may come and find the rmap count decremented
+			 * before the pte is switched to the new page, and
+			 * "reuse" the old page writing into it while our pte
+			 * here still points into it and can be read by other
+			 * threads.
+			 *
+			 * The critical issue is to order this
+			 * page_remove_rmap with the ptp_clear_flush above.
+			 * Those stores are ordered by (if nothing else,)
+			 * the barrier present in the atomic_add_negative
+			 * in page_remove_rmap.
+			 *
+			 * Then the TLB flush in ptep_clear_flush ensures that
+			 * no process can access the old page before the
+			 * decremented mapcount is visible. And the old page
+			 * cannot be reused until after the decremented
+			 * mapcount is visible. So transitively, TLBs to
+			 * old page will be flushed before it can be reused.
+			 */
+			page_remove_rmap(old_page, false);
+		}
+
+		/* Free the old page.. */
+		new_page = old_page;
+		page_copied = 1;
+	} else {
+		mem_cgroup_cancel_charge(new_page, memcg, false);
+	}
+
+	if (new_page)
+		put_page(new_page);
+
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	/*
+	 * No need to double call mmu_notifier->invalidate_range() callback as
+	 * the above ptep_clear_flush_notify() did already call it.
+	 */
+	mmu_notifier_invalidate_range_only_end(mm, mmun_start, mmun_end);
+	if (old_page) {
+		/*
+		 * Don't let another task, with possibly unlocked vma,
+		 * keep the mlocked page.
+		 */
+		if (page_copied && (vma->vm_flags & VM_LOCKED)) {
+			lock_page(old_page);	/* LRU manipulation */
+			if (PageMlocked(old_page))
+				munlock_vma_page(old_page);
+			unlock_page(old_page);
+		}
+		put_page(old_page);
+	}
+	return page_copied ? VM_FAULT_WRITE : 0;
+oom_free_new:
+	put_page(new_page);
+oom:
+	if (old_page)
+		put_page(old_page);
+	return VM_FAULT_OOM;
+}
+
+/**
+ * finish_mkwrite_fault - finish page fault for a shared mapping, making PTE
+ *			  writeable once the page is prepared
+ *
+ * @vmf: structure describing the fault
+ *
+ * This function handles all that is needed to finish a write page fault in a
+ * shared mapping due to PTE being read-only once the mapped page is prepared.
+ * It handles locking of PTE and modifying it. The function returns
+ * VM_FAULT_WRITE on success, 0 when PTE got changed before we acquired PTE
+ * lock.
+ *
+ * The function expects the page to be locked or other protection against
+ * concurrent faults / writeback (such as DAX radix tree locks).
+ */
+vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf)
+{
+	WARN_ON_ONCE(!(vmf->vma->vm_flags & VM_SHARED));
+	vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, vmf->address,
+				       &vmf->ptl);
+	/*
+	 * We might have raced with another page fault while we released the
+	 * pte_offset_map_lock.
+	 */
+	if (!pte_same(*vmf->pte, vmf->orig_pte)) {
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		return VM_FAULT_NOPAGE;
+	}
+	wp_page_reuse(vmf);
+	return 0;
+}
+
+/*
+ * Handle write page faults for VM_MIXEDMAP or VM_PFNMAP for a VM_SHARED
+ * mapping
+ */
+static vm_fault_t wp_pfn_shared(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+
+	if (vma->vm_ops && vma->vm_ops->pfn_mkwrite) {
+		vm_fault_t ret;
+
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		vmf->flags |= FAULT_FLAG_MKWRITE;
+		ret = vma->vm_ops->pfn_mkwrite(vmf);
+		if (ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))
+			return ret;
+		return finish_mkwrite_fault(vmf);
+	}
+	wp_page_reuse(vmf);
+	return VM_FAULT_WRITE;
+}
+
+static vm_fault_t wp_page_shared(struct vm_fault *vmf)
+	__releases(vmf->ptl)
+{
+	struct vm_area_struct *vma = vmf->vma;
+
+	get_page(vmf->page);
+
+	if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
+		vm_fault_t tmp;
+
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		tmp = do_page_mkwrite(vmf);
+		if (unlikely(!tmp || (tmp &
+				      (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
+			put_page(vmf->page);
+			return tmp;
+		}
+		tmp = finish_mkwrite_fault(vmf);
+		if (unlikely(tmp & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
+			unlock_page(vmf->page);
+			put_page(vmf->page);
+			return tmp;
+		}
+	} else {
+		wp_page_reuse(vmf);
+		lock_page(vmf->page);
+	}
+	fault_dirty_shared_page(vma, vmf->page);
+	put_page(vmf->page);
+
+	return VM_FAULT_WRITE;
+}
+
+/*
+ * This routine handles present pages, when users try to write
+ * to a shared page. It is done by copying the page to a new address
+ * and decrementing the shared-page counter for the old page.
+ *
+ * Note that this routine assumes that the protection checks have been
+ * done by the caller (the low-level page fault routine in most cases).
+ * Thus we can safely just mark it writable once we've done any necessary
+ * COW.
+ *
+ * We also mark the page dirty at this point even though the page will
+ * change only once the write actually happens. This avoids a few races,
+ * and potentially makes it more efficient.
+ *
+ * We enter with non-exclusive mmap_sem (to exclude vma changes,
+ * but allow concurrent faults), with pte both mapped and locked.
+ * We return with mmap_sem still held, but pte unmapped and unlocked.
+ */
+static vm_fault_t do_wp_page(struct vm_fault *vmf)
+	__releases(vmf->ptl)
+{
+	struct vm_area_struct *vma = vmf->vma;
+
+	vmf->page = vm_normal_page(vma, vmf->address, vmf->orig_pte);
+	if (!vmf->page) {
+		/*
+		 * VM_MIXEDMAP !pfn_valid() case, or VM_SOFTDIRTY clear on a
+		 * VM_PFNMAP VMA.
+		 *
+		 * We should not cow pages in a shared writeable mapping.
+		 * Just mark the pages writable and/or call ops->pfn_mkwrite.
+		 */
+		if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
+				     (VM_WRITE|VM_SHARED))
+			return wp_pfn_shared(vmf);
+
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		return wp_page_copy(vmf);
+	}
+
+	/*
+	 * Take out anonymous pages first, anonymous shared vmas are
+	 * not dirty accountable.
+	 */
+	if (PageAnon(vmf->page) && !PageKsm(vmf->page)) {
+		int total_map_swapcount;
+		if (!trylock_page(vmf->page)) {
+			get_page(vmf->page);
+			pte_unmap_unlock(vmf->pte, vmf->ptl);
+			lock_page(vmf->page);
+			vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
+					vmf->address, &vmf->ptl);
+			if (!pte_same(*vmf->pte, vmf->orig_pte)) {
+				unlock_page(vmf->page);
+				pte_unmap_unlock(vmf->pte, vmf->ptl);
+				put_page(vmf->page);
+				return 0;
+			}
+			put_page(vmf->page);
+		}
+		if (reuse_swap_page(vmf->page, &total_map_swapcount)) {
+			if (total_map_swapcount == 1) {
+				/*
+				 * The page is all ours. Move it to
+				 * our anon_vma so the rmap code will
+				 * not search our parent or siblings.
+				 * Protected against the rmap code by
+				 * the page lock.
+				 */
+				page_move_anon_rmap(vmf->page, vma);
+			}
+			unlock_page(vmf->page);
+			wp_page_reuse(vmf);
+			return VM_FAULT_WRITE;
+		}
+		unlock_page(vmf->page);
+	} else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
+					(VM_WRITE|VM_SHARED))) {
+		return wp_page_shared(vmf);
+	}
+
+	/*
+	 * Ok, we need to copy. Oh, well..
+	 */
+	get_page(vmf->page);
+
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	return wp_page_copy(vmf);
+}
+
+static void unmap_mapping_range_vma(struct vm_area_struct *vma,
+		unsigned long start_addr, unsigned long end_addr,
+		struct zap_details *details)
+{
+	zap_page_range_single(vma, start_addr, end_addr - start_addr, details);
+}
+
+static inline void unmap_mapping_range_tree(struct rb_root_cached *root,
+					    struct zap_details *details)
+{
+	struct vm_area_struct *vma;
+	pgoff_t vba, vea, zba, zea;
+
+	vma_interval_tree_foreach(vma, root,
+			details->first_index, details->last_index) {
+
+		vba = vma->vm_pgoff;
+		vea = vba + vma_pages(vma) - 1;
+		zba = details->first_index;
+		if (zba < vba)
+			zba = vba;
+		zea = details->last_index;
+		if (zea > vea)
+			zea = vea;
+
+		unmap_mapping_range_vma(vma,
+			((zba - vba) << PAGE_SHIFT) + vma->vm_start,
+			((zea - vba + 1) << PAGE_SHIFT) + vma->vm_start,
+				details);
+	}
+}
+
+/**
+ * unmap_mapping_page() - Unmap single page from processes.
+ * @page: The locked page to be unmapped.
+ *
+ * Unmap this page from any userspace process which still has it mmaped.
+ * Typically, for efficiency, the range of nearby pages has already been
+ * unmapped by unmap_mapping_pages() or unmap_mapping_range().  But once
+ * truncation or invalidation holds the lock on a page, it may find that
+ * the page has been remapped again: and then uses unmap_mapping_page()
+ * to unmap it finally.
+ */
+void unmap_mapping_page(struct page *page)
+{
+	struct address_space *mapping = page->mapping;
+	struct zap_details details = { };
+
+	VM_BUG_ON(!PageLocked(page));
+	VM_BUG_ON(PageTail(page));
+
+	details.check_mapping = mapping;
+	details.first_index = page->index;
+	details.last_index = page->index + hpage_nr_pages(page) - 1;
+	details.single_page = page;
+
+	i_mmap_lock_write(mapping);
+	if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))
+		unmap_mapping_range_tree(&mapping->i_mmap, &details);
+	i_mmap_unlock_write(mapping);
+}
+
+/**
+ * unmap_mapping_pages() - Unmap pages from processes.
+ * @mapping: The address space containing pages to be unmapped.
+ * @start: Index of first page to be unmapped.
+ * @nr: Number of pages to be unmapped.  0 to unmap to end of file.
+ * @even_cows: Whether to unmap even private COWed pages.
+ *
+ * Unmap the pages in this address space from any userspace process which
+ * has them mmaped.  Generally, you want to remove COWed pages as well when
+ * a file is being truncated, but not when invalidating pages from the page
+ * cache.
+ */
+void unmap_mapping_pages(struct address_space *mapping, pgoff_t start,
+		pgoff_t nr, bool even_cows)
+{
+	struct zap_details details = { };
+
+	details.check_mapping = even_cows ? NULL : mapping;
+	details.first_index = start;
+	details.last_index = start + nr - 1;
+	if (details.last_index < details.first_index)
+		details.last_index = ULONG_MAX;
+
+	i_mmap_lock_write(mapping);
+	if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))
+		unmap_mapping_range_tree(&mapping->i_mmap, &details);
+	i_mmap_unlock_write(mapping);
+}
+
+/**
+ * unmap_mapping_range - unmap the portion of all mmaps in the specified
+ * address_space corresponding to the specified byte range in the underlying
+ * file.
+ *
+ * @mapping: the address space containing mmaps to be unmapped.
+ * @holebegin: byte in first page to unmap, relative to the start of
+ * the underlying file.  This will be rounded down to a PAGE_SIZE
+ * boundary.  Note that this is different from truncate_pagecache(), which
+ * must keep the partial page.  In contrast, we must get rid of
+ * partial pages.
+ * @holelen: size of prospective hole in bytes.  This will be rounded
+ * up to a PAGE_SIZE boundary.  A holelen of zero truncates to the
+ * end of the file.
+ * @even_cows: 1 when truncating a file, unmap even private COWed pages;
+ * but 0 when invalidating pagecache, don't throw away private data.
+ */
+void unmap_mapping_range(struct address_space *mapping,
+		loff_t const holebegin, loff_t const holelen, int even_cows)
+{
+	pgoff_t hba = holebegin >> PAGE_SHIFT;
+	pgoff_t hlen = (holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
+
+	/* Check for overflow. */
+	if (sizeof(holelen) > sizeof(hlen)) {
+		long long holeend =
+			(holebegin + holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		if (holeend & ~(long long)ULONG_MAX)
+			hlen = ULONG_MAX - hba + 1;
+	}
+
+	unmap_mapping_pages(mapping, hba, hlen, even_cows);
+}
+EXPORT_SYMBOL(unmap_mapping_range);
+
+/*
+ * We enter with non-exclusive mmap_sem (to exclude vma changes,
+ * but allow concurrent faults), and pte mapped but not yet locked.
+ * We return with pte unmapped and unlocked.
+ *
+ * We return with the mmap_sem locked or unlocked in the same cases
+ * as does filemap_fault().
+ */
+vm_fault_t do_swap_page(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct page *page = NULL, *swapcache;
+	struct mem_cgroup *memcg;
+	swp_entry_t entry;
+	pte_t pte;
+	int locked;
+	int exclusive = 0;
+	vm_fault_t ret = 0;
+
+	if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte))
+		goto out;
+
+	entry = pte_to_swp_entry(vmf->orig_pte);
+	if (unlikely(non_swap_entry(entry))) {
+		if (is_migration_entry(entry)) {
+			migration_entry_wait(vma->vm_mm, vmf->pmd,
+					     vmf->address);
+		} else if (is_device_private_entry(entry)) {
+			/*
+			 * For un-addressable device memory we call the pgmap
+			 * fault handler callback. The callback must migrate
+			 * the page back to some CPU accessible page.
+			 */
+			ret = device_private_entry_fault(vma, vmf->address, entry,
+						 vmf->flags, vmf->pmd);
+		} else if (is_hwpoison_entry(entry)) {
+			ret = VM_FAULT_HWPOISON;
+		} else {
+			print_bad_pte(vma, vmf->address, vmf->orig_pte, NULL);
+			ret = VM_FAULT_SIGBUS;
+		}
+		goto out;
+	}
+
+
+	delayacct_set_flag(DELAYACCT_PF_SWAPIN);
+	page = lookup_swap_cache(entry, vma, vmf->address);
+	swapcache = page;
+
+	if (!page) {
+		struct swap_info_struct *si = swp_swap_info(entry);
+
+		if (si->flags & SWP_SYNCHRONOUS_IO &&
+				__swap_count(si, entry) == 1) {
+			/* skip swapcache */
+			page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma,
+							vmf->address);
+			if (page) {
+				__SetPageLocked(page);
+				__SetPageSwapBacked(page);
+				set_page_private(page, entry.val);
+				lru_cache_add_anon(page);
+				swap_readpage(page, true);
+			}
+		} else {
+			page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
+						vmf);
+			swapcache = page;
+		}
+
+		if (!page) {
+			/*
+			 * Back out if somebody else faulted in this pte
+			 * while we released the pte lock.
+			 */
+			vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
+					vmf->address, &vmf->ptl);
+			if (likely(pte_same(*vmf->pte, vmf->orig_pte)))
+				ret = VM_FAULT_OOM;
+			delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
+			goto unlock;
+		}
+
+		/* Had to read the page from swap area: Major fault */
+		ret = VM_FAULT_MAJOR;
+		count_vm_event(PGMAJFAULT);
+		count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
+	} else if (PageHWPoison(page)) {
+		/*
+		 * hwpoisoned dirty swapcache pages are kept for killing
+		 * owner processes (which may be unknown at hwpoison time)
+		 */
+		ret = VM_FAULT_HWPOISON;
+		delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
+		goto out_release;
+	}
+
+	locked = lock_page_or_retry(page, vma->vm_mm, vmf->flags);
+
+	delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
+	if (!locked) {
+		ret |= VM_FAULT_RETRY;
+		goto out_release;
+	}
+
+	/*
+	 * Make sure try_to_free_swap or reuse_swap_page or swapoff did not
+	 * release the swapcache from under us.  The page pin, and pte_same
+	 * test below, are not enough to exclude that.  Even if it is still
+	 * swapcache, we need to check that the page's swap has not changed.
+	 */
+	if (unlikely((!PageSwapCache(page) ||
+			page_private(page) != entry.val)) && swapcache)
+		goto out_page;
+
+	page = ksm_might_need_to_copy(page, vma, vmf->address);
+	if (unlikely(!page)) {
+		ret = VM_FAULT_OOM;
+		page = swapcache;
+		goto out_page;
+	}
+
+	if (mem_cgroup_try_charge_delay(page, vma->vm_mm, GFP_KERNEL,
+					&memcg, false)) {
+		ret = VM_FAULT_OOM;
+		goto out_page;
+	}
+
+	/*
+	 * Back out if somebody else already faulted in this pte.
+	 */
+	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
+			&vmf->ptl);
+	if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte)))
+		goto out_nomap;
+
+	if (unlikely(!PageUptodate(page))) {
+		ret = VM_FAULT_SIGBUS;
+		goto out_nomap;
+	}
+
+	/*
+	 * The page isn't present yet, go ahead with the fault.
+	 *
+	 * Be careful about the sequence of operations here.
+	 * To get its accounting right, reuse_swap_page() must be called
+	 * while the page is counted on swap but not yet in mapcount i.e.
+	 * before page_add_anon_rmap() and swap_free(); try_to_free_swap()
+	 * must be called after the swap_free(), or it will never succeed.
+	 */
+
+	inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
+	dec_mm_counter_fast(vma->vm_mm, MM_SWAPENTS);
+	pte = mk_pte(page, vma->vm_page_prot);
+	if ((vmf->flags & FAULT_FLAG_WRITE) && reuse_swap_page(page, NULL)) {
+		pte = maybe_mkwrite(pte_mkdirty(pte), vma);
+		vmf->flags &= ~FAULT_FLAG_WRITE;
+		ret |= VM_FAULT_WRITE;
+		exclusive = RMAP_EXCLUSIVE;
+	}
+	flush_icache_page(vma, page);
+	if (pte_swp_soft_dirty(vmf->orig_pte))
+		pte = pte_mksoft_dirty(pte);
+	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
+	arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte);
+	vmf->orig_pte = pte;
+
+	/* ksm created a completely new copy */
+	if (unlikely(page != swapcache && swapcache)) {
+		page_add_new_anon_rmap(page, vma, vmf->address, false);
+		mem_cgroup_commit_charge(page, memcg, false, false);
+		lru_cache_add_active_or_unevictable(page, vma);
+	} else {
+		do_page_add_anon_rmap(page, vma, vmf->address, exclusive);
+		mem_cgroup_commit_charge(page, memcg, true, false);
+		activate_page(page);
+	}
+
+	swap_free(entry);
+	if (mem_cgroup_swap_full(page) ||
+	    (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
+		try_to_free_swap(page);
+	unlock_page(page);
+	if (page != swapcache && swapcache) {
+		/*
+		 * Hold the lock to avoid the swap entry to be reused
+		 * until we take the PT lock for the pte_same() check
+		 * (to avoid false positives from pte_same). For
+		 * further safety release the lock after the swap_free
+		 * so that the swap count won't change under a
+		 * parallel locked swapcache.
+		 */
+		unlock_page(swapcache);
+		put_page(swapcache);
+	}
+
+	if (vmf->flags & FAULT_FLAG_WRITE) {
+		ret |= do_wp_page(vmf);
+		if (ret & VM_FAULT_ERROR)
+			ret &= VM_FAULT_ERROR;
+		goto out;
+	}
+
+	/* No need to invalidate - it was non-present before */
+	update_mmu_cache(vma, vmf->address, vmf->pte);
+unlock:
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+out:
+	return ret;
+out_nomap:
+	mem_cgroup_cancel_charge(page, memcg, false);
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+out_page:
+	unlock_page(page);
+out_release:
+	put_page(page);
+	if (page != swapcache && swapcache) {
+		unlock_page(swapcache);
+		put_page(swapcache);
+	}
+	return ret;
+}
+
+/*
+ * We enter with non-exclusive mmap_sem (to exclude vma changes,
+ * but allow concurrent faults), and pte mapped but not yet locked.
+ * We return with mmap_sem still held, but pte unmapped and unlocked.
+ */
+static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct mem_cgroup *memcg;
+	struct page *page;
+	vm_fault_t ret = 0;
+	pte_t entry;
+
+	/* File mapping without ->vm_ops ? */
+	if (vma->vm_flags & VM_SHARED)
+		return VM_FAULT_SIGBUS;
+
+	/*
+	 * Use pte_alloc() instead of pte_alloc_map().  We can't run
+	 * pte_offset_map() on pmds where a huge pmd might be created
+	 * from a different thread.
+	 *
+	 * pte_alloc_map() is safe to use under down_write(mmap_sem) or when
+	 * parallel threads are excluded by other means.
+	 *
+	 * Here we only have down_read(mmap_sem).
+	 */
+	if (pte_alloc(vma->vm_mm, vmf->pmd, vmf->address))
+		return VM_FAULT_OOM;
+
+	/* See the comment in pte_alloc_one_map() */
+	if (unlikely(pmd_trans_unstable(vmf->pmd)))
+		return 0;
+
+	/* Use the zero-page for reads */
+	if (!(vmf->flags & FAULT_FLAG_WRITE) &&
+			!mm_forbids_zeropage(vma->vm_mm)) {
+		entry = pte_mkspecial(pfn_pte(my_zero_pfn(vmf->address),
+						vma->vm_page_prot));
+		vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
+				vmf->address, &vmf->ptl);
+		if (!pte_none(*vmf->pte))
+			goto unlock;
+		ret = check_stable_address_space(vma->vm_mm);
+		if (ret)
+			goto unlock;
+		/* Deliver the page fault to userland, check inside PT lock */
+		if (userfaultfd_missing(vma)) {
+			pte_unmap_unlock(vmf->pte, vmf->ptl);
+			return handle_userfault(vmf, VM_UFFD_MISSING);
+		}
+		goto setpte;
+	}
+
+	/* Allocate our own private page. */
+	if (unlikely(anon_vma_prepare(vma)))
+		goto oom;
+	page = alloc_zeroed_user_highpage_movable(vma, vmf->address);
+	if (!page)
+		goto oom;
+
+	if (mem_cgroup_try_charge_delay(page, vma->vm_mm, GFP_KERNEL, &memcg,
+					false))
+		goto oom_free_page;
+
+	/*
+	 * The memory barrier inside __SetPageUptodate makes sure that
+	 * preceeding stores to the page contents become visible before
+	 * the set_pte_at() write.
+	 */
+	__SetPageUptodate(page);
+
+	entry = mk_pte(page, vma->vm_page_prot);
+	if (vma->vm_flags & VM_WRITE)
+		entry = pte_mkwrite(pte_mkdirty(entry));
+
+	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
+			&vmf->ptl);
+	if (!pte_none(*vmf->pte))
+		goto release;
+
+	ret = check_stable_address_space(vma->vm_mm);
+	if (ret)
+		goto release;
+
+	/* Deliver the page fault to userland, check inside PT lock */
+	if (userfaultfd_missing(vma)) {
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		mem_cgroup_cancel_charge(page, memcg, false);
+		put_page(page);
+		return handle_userfault(vmf, VM_UFFD_MISSING);
+	}
+
+	inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
+	page_add_new_anon_rmap(page, vma, vmf->address, false);
+	mem_cgroup_commit_charge(page, memcg, false, false);
+	lru_cache_add_active_or_unevictable(page, vma);
+setpte:
+	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry);
+
+	/* No need to invalidate - it was non-present before */
+	update_mmu_cache(vma, vmf->address, vmf->pte);
+unlock:
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	return ret;
+release:
+	mem_cgroup_cancel_charge(page, memcg, false);
+	put_page(page);
+	goto unlock;
+oom_free_page:
+	put_page(page);
+oom:
+	return VM_FAULT_OOM;
+}
+
+/*
+ * The mmap_sem must have been held on entry, and may have been
+ * released depending on flags and vma->vm_ops->fault() return value.
+ * See filemap_fault() and __lock_page_retry().
+ */
+static vm_fault_t __do_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	vm_fault_t ret;
+
+	/*
+	 * Preallocate pte before we take page_lock because this might lead to
+	 * deadlocks for memcg reclaim which waits for pages under writeback:
+	 *				lock_page(A)
+	 *				SetPageWriteback(A)
+	 *				unlock_page(A)
+	 * lock_page(B)
+	 *				lock_page(B)
+	 * pte_alloc_pne
+	 *   shrink_page_list
+	 *     wait_on_page_writeback(A)
+	 *				SetPageWriteback(B)
+	 *				unlock_page(B)
+	 *				# flush A, B to clear the writeback
+	 */
+	if (pmd_none(*vmf->pmd) && !vmf->prealloc_pte) {
+		vmf->prealloc_pte = pte_alloc_one(vmf->vma->vm_mm,
+						  vmf->address);
+		if (!vmf->prealloc_pte)
+			return VM_FAULT_OOM;
+		smp_wmb(); /* See comment in __pte_alloc() */
+	}
+
+	ret = vma->vm_ops->fault(vmf);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY |
+			    VM_FAULT_DONE_COW)))
+		return ret;
+
+	if (unlikely(PageHWPoison(vmf->page))) {
+		struct page *page = vmf->page;
+		vm_fault_t poisonret = VM_FAULT_HWPOISON;
+		if (ret & VM_FAULT_LOCKED) {
+			if (page_mapped(page))
+				unmap_mapping_pages(page_mapping(page),
+						    page->index, 1, false);
+			/* Retry if a clean page was removed from the cache. */
+			if (invalidate_inode_page(page))
+				poisonret = VM_FAULT_NOPAGE;
+			unlock_page(page);
+		}
+		put_page(page);
+		vmf->page = NULL;
+		return poisonret;
+	}
+
+	if (unlikely(!(ret & VM_FAULT_LOCKED)))
+		lock_page(vmf->page);
+	else
+		VM_BUG_ON_PAGE(!PageLocked(vmf->page), vmf->page);
+
+	return ret;
+}
+
+/*
+ * The ordering of these checks is important for pmds with _PAGE_DEVMAP set.
+ * If we check pmd_trans_unstable() first we will trip the bad_pmd() check
+ * inside of pmd_none_or_trans_huge_or_clear_bad(). This will end up correctly
+ * returning 1 but not before it spams dmesg with the pmd_clear_bad() output.
+ */
+static int pmd_devmap_trans_unstable(pmd_t *pmd)
+{
+	return pmd_devmap(*pmd) || pmd_trans_unstable(pmd);
+}
+
+static vm_fault_t pte_alloc_one_map(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+
+	if (!pmd_none(*vmf->pmd))
+		goto map_pte;
+	if (vmf->prealloc_pte) {
+		vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
+		if (unlikely(!pmd_none(*vmf->pmd))) {
+			spin_unlock(vmf->ptl);
+			goto map_pte;
+		}
+
+		mm_inc_nr_ptes(vma->vm_mm);
+		pmd_populate(vma->vm_mm, vmf->pmd, vmf->prealloc_pte);
+		spin_unlock(vmf->ptl);
+		vmf->prealloc_pte = NULL;
+	} else if (unlikely(pte_alloc(vma->vm_mm, vmf->pmd, vmf->address))) {
+		return VM_FAULT_OOM;
+	}
+map_pte:
+	/*
+	 * If a huge pmd materialized under us just retry later.  Use
+	 * pmd_trans_unstable() via pmd_devmap_trans_unstable() instead of
+	 * pmd_trans_huge() to ensure the pmd didn't become pmd_trans_huge
+	 * under us and then back to pmd_none, as a result of MADV_DONTNEED
+	 * running immediately after a huge pmd fault in a different thread of
+	 * this mm, in turn leading to a misleading pmd_trans_huge() retval.
+	 * All we have to ensure is that it is a regular pmd that we can walk
+	 * with pte_offset_map() and we can do that through an atomic read in
+	 * C, which is what pmd_trans_unstable() provides.
+	 */
+	if (pmd_devmap_trans_unstable(vmf->pmd))
+		return VM_FAULT_NOPAGE;
+
+	/*
+	 * At this point we know that our vmf->pmd points to a page of ptes
+	 * and it cannot become pmd_none(), pmd_devmap() or pmd_trans_huge()
+	 * for the duration of the fault.  If a racing MADV_DONTNEED runs and
+	 * we zap the ptes pointed to by our vmf->pmd, the vmf->ptl will still
+	 * be valid and we will re-check to make sure the vmf->pte isn't
+	 * pte_none() under vmf->ptl protection when we return to
+	 * alloc_set_pte().
+	 */
+	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
+			&vmf->ptl);
+	return 0;
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
+
+#define HPAGE_CACHE_INDEX_MASK (HPAGE_PMD_NR - 1)
+static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
+		unsigned long haddr)
+{
+	if (((vma->vm_start >> PAGE_SHIFT) & HPAGE_CACHE_INDEX_MASK) !=
+			(vma->vm_pgoff & HPAGE_CACHE_INDEX_MASK))
+		return false;
+	if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
+		return false;
+	return true;
+}
+
+static void deposit_prealloc_pte(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+
+	pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, vmf->prealloc_pte);
+	/*
+	 * We are going to consume the prealloc table,
+	 * count that as nr_ptes.
+	 */
+	mm_inc_nr_ptes(vma->vm_mm);
+	vmf->prealloc_pte = NULL;
+}
+
+static vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	bool write = vmf->flags & FAULT_FLAG_WRITE;
+	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
+	pmd_t entry;
+	int i;
+	vm_fault_t ret;
+
+	if (!transhuge_vma_suitable(vma, haddr))
+		return VM_FAULT_FALLBACK;
+
+	ret = VM_FAULT_FALLBACK;
+	page = compound_head(page);
+
+	/*
+	 * Archs like ppc64 need additonal space to store information
+	 * related to pte entry. Use the preallocated table for that.
+	 */
+	if (arch_needs_pgtable_deposit() && !vmf->prealloc_pte) {
+		vmf->prealloc_pte = pte_alloc_one(vma->vm_mm, vmf->address);
+		if (!vmf->prealloc_pte)
+			return VM_FAULT_OOM;
+		smp_wmb(); /* See comment in __pte_alloc() */
+	}
+
+	vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
+	if (unlikely(!pmd_none(*vmf->pmd)))
+		goto out;
+
+	for (i = 0; i < HPAGE_PMD_NR; i++)
+		flush_icache_page(vma, page + i);
+
+	entry = mk_huge_pmd(page, vma->vm_page_prot);
+	if (write)
+		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
+
+	add_mm_counter(vma->vm_mm, mm_counter_file(page), HPAGE_PMD_NR);
+	page_add_file_rmap(page, true);
+	/*
+	 * deposit and withdraw with pmd lock held
+	 */
+	if (arch_needs_pgtable_deposit())
+		deposit_prealloc_pte(vmf);
+
+	set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
+
+	update_mmu_cache_pmd(vma, haddr, vmf->pmd);
+
+	/* fault is handled */
+	ret = 0;
+	count_vm_event(THP_FILE_MAPPED);
+out:
+	spin_unlock(vmf->ptl);
+	return ret;
+}
+#else
+static vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
+{
+	BUILD_BUG();
+	return 0;
+}
+#endif
+
+/**
+ * alloc_set_pte - setup new PTE entry for given page and add reverse page
+ * mapping. If needed, the fucntion allocates page table or use pre-allocated.
+ *
+ * @vmf: fault environment
+ * @memcg: memcg to charge page (only for private mappings)
+ * @page: page to map
+ *
+ * Caller must take care of unlocking vmf->ptl, if vmf->pte is non-NULL on
+ * return.
+ *
+ * Target users are page handler itself and implementations of
+ * vm_ops->map_pages.
+ */
+vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
+		struct page *page)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	bool write = vmf->flags & FAULT_FLAG_WRITE;
+	pte_t entry;
+	vm_fault_t ret;
+
+	if (pmd_none(*vmf->pmd) && PageTransCompound(page) &&
+			IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE)) {
+		/* THP on COW? */
+		VM_BUG_ON_PAGE(memcg, page);
+
+		ret = do_set_pmd(vmf, page);
+		if (ret != VM_FAULT_FALLBACK)
+			return ret;
+	}
+
+	if (!vmf->pte) {
+		ret = pte_alloc_one_map(vmf);
+		if (ret)
+			return ret;
+	}
+
+	/* Re-check under ptl */
+	if (unlikely(!pte_none(*vmf->pte)))
+		return VM_FAULT_NOPAGE;
+
+	flush_icache_page(vma, page);
+	entry = mk_pte(page, vma->vm_page_prot);
+	if (write)
+		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+	/* copy-on-write page */
+	if (write && !(vma->vm_flags & VM_SHARED)) {
+		inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
+		page_add_new_anon_rmap(page, vma, vmf->address, false);
+		mem_cgroup_commit_charge(page, memcg, false, false);
+		lru_cache_add_active_or_unevictable(page, vma);
+	} else {
+		inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page));
+		page_add_file_rmap(page, false);
+	}
+	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry);
+
+	/* no need to invalidate: a not-present page won't be cached */
+	update_mmu_cache(vma, vmf->address, vmf->pte);
+
+	return 0;
+}
+
+
+/**
+ * finish_fault - finish page fault once we have prepared the page to fault
+ *
+ * @vmf: structure describing the fault
+ *
+ * This function handles all that is needed to finish a page fault once the
+ * page to fault in is prepared. It handles locking of PTEs, inserts PTE for
+ * given page, adds reverse page mapping, handles memcg charges and LRU
+ * addition. The function returns 0 on success, VM_FAULT_ code in case of
+ * error.
+ *
+ * The function expects the page to be locked and on success it consumes a
+ * reference of a page being mapped (for the PTE which maps it).
+ */
+vm_fault_t finish_fault(struct vm_fault *vmf)
+{
+	struct page *page;
+	vm_fault_t ret = 0;
+
+	/* Did we COW the page? */
+	if ((vmf->flags & FAULT_FLAG_WRITE) &&
+	    !(vmf->vma->vm_flags & VM_SHARED))
+		page = vmf->cow_page;
+	else
+		page = vmf->page;
+
+	/*
+	 * check even for read faults because we might have lost our CoWed
+	 * page
+	 */
+	if (!(vmf->vma->vm_flags & VM_SHARED))
+		ret = check_stable_address_space(vmf->vma->vm_mm);
+	if (!ret)
+		ret = alloc_set_pte(vmf, vmf->memcg, page);
+	if (vmf->pte)
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+	return ret;
+}
+
+static unsigned long fault_around_bytes __read_mostly =
+	rounddown_pow_of_two(65536);
+
+#ifdef CONFIG_DEBUG_FS
+static int fault_around_bytes_get(void *data, u64 *val)
+{
+	*val = fault_around_bytes;
+	return 0;
+}
+
+/*
+ * fault_around_bytes must be rounded down to the nearest page order as it's
+ * what do_fault_around() expects to see.
+ */
+static int fault_around_bytes_set(void *data, u64 val)
+{
+	if (val / PAGE_SIZE > PTRS_PER_PTE)
+		return -EINVAL;
+	if (val > PAGE_SIZE)
+		fault_around_bytes = rounddown_pow_of_two(val);
+	else
+		fault_around_bytes = PAGE_SIZE; /* rounddown_pow_of_two(0) is undefined */
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(fault_around_bytes_fops,
+		fault_around_bytes_get, fault_around_bytes_set, "%llu\n");
+
+static int __init fault_around_debugfs(void)
+{
+	void *ret;
+
+	ret = debugfs_create_file_unsafe("fault_around_bytes", 0644, NULL, NULL,
+			&fault_around_bytes_fops);
+	if (!ret)
+		pr_warn("Failed to create fault_around_bytes in debugfs");
+	return 0;
+}
+late_initcall(fault_around_debugfs);
+#endif
+
+/*
+ * do_fault_around() tries to map few pages around the fault address. The hope
+ * is that the pages will be needed soon and this will lower the number of
+ * faults to handle.
+ *
+ * It uses vm_ops->map_pages() to map the pages, which skips the page if it's
+ * not ready to be mapped: not up-to-date, locked, etc.
+ *
+ * This function is called with the page table lock taken. In the split ptlock
+ * case the page table lock only protects only those entries which belong to
+ * the page table corresponding to the fault address.
+ *
+ * This function doesn't cross the VMA boundaries, in order to call map_pages()
+ * only once.
+ *
+ * fault_around_bytes defines how many bytes we'll try to map.
+ * do_fault_around() expects it to be set to a power of two less than or equal
+ * to PTRS_PER_PTE.
+ *
+ * The virtual address of the area that we map is naturally aligned to
+ * fault_around_bytes rounded down to the machine page size
+ * (and therefore to page order).  This way it's easier to guarantee
+ * that we don't cross page table boundaries.
+ */
+static vm_fault_t do_fault_around(struct vm_fault *vmf)
+{
+	unsigned long address = vmf->address, nr_pages, mask;
+	pgoff_t start_pgoff = vmf->pgoff;
+	pgoff_t end_pgoff;
+	int off;
+	vm_fault_t ret = 0;
+
+	nr_pages = READ_ONCE(fault_around_bytes) >> PAGE_SHIFT;
+	mask = ~(nr_pages * PAGE_SIZE - 1) & PAGE_MASK;
+
+	vmf->address = max(address & mask, vmf->vma->vm_start);
+	off = ((address - vmf->address) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
+	start_pgoff -= off;
+
+	/*
+	 *  end_pgoff is either the end of the page table, the end of
+	 *  the vma or nr_pages from start_pgoff, depending what is nearest.
+	 */
+	end_pgoff = start_pgoff -
+		((vmf->address >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)) +
+		PTRS_PER_PTE - 1;
+	end_pgoff = min3(end_pgoff, vma_pages(vmf->vma) + vmf->vma->vm_pgoff - 1,
+			start_pgoff + nr_pages - 1);
+
+	if (pmd_none(*vmf->pmd)) {
+		vmf->prealloc_pte = pte_alloc_one(vmf->vma->vm_mm,
+						  vmf->address);
+		if (!vmf->prealloc_pte)
+			goto out;
+		smp_wmb(); /* See comment in __pte_alloc() */
+	}
+
+	vmf->vma->vm_ops->map_pages(vmf, start_pgoff, end_pgoff);
+
+	/* Huge page is mapped? Page fault is solved */
+	if (pmd_trans_huge(*vmf->pmd)) {
+		ret = VM_FAULT_NOPAGE;
+		goto out;
+	}
+
+	/* ->map_pages() haven't done anything useful. Cold page cache? */
+	if (!vmf->pte)
+		goto out;
+
+	/* check if the page fault is solved */
+	vmf->pte -= (vmf->address >> PAGE_SHIFT) - (address >> PAGE_SHIFT);
+	if (!pte_none(*vmf->pte))
+		ret = VM_FAULT_NOPAGE;
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+out:
+	vmf->address = address;
+	vmf->pte = NULL;
+	return ret;
+}
+
+static vm_fault_t do_read_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	vm_fault_t ret = 0;
+
+	/*
+	 * Let's call ->map_pages() first and use ->fault() as fallback
+	 * if page by the offset is not ready to be mapped (cold cache or
+	 * something).
+	 */
+	if (vma->vm_ops->map_pages && fault_around_bytes >> PAGE_SHIFT > 1) {
+		ret = do_fault_around(vmf);
+		if (ret)
+			return ret;
+	}
+
+	ret = __do_fault(vmf);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		return ret;
+
+	ret |= finish_fault(vmf);
+	unlock_page(vmf->page);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		put_page(vmf->page);
+	return ret;
+}
+
+static vm_fault_t do_cow_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	vm_fault_t ret;
+
+	if (unlikely(anon_vma_prepare(vma)))
+		return VM_FAULT_OOM;
+
+	vmf->cow_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vmf->address);
+	if (!vmf->cow_page)
+		return VM_FAULT_OOM;
+
+	if (mem_cgroup_try_charge_delay(vmf->cow_page, vma->vm_mm, GFP_KERNEL,
+				&vmf->memcg, false)) {
+		put_page(vmf->cow_page);
+		return VM_FAULT_OOM;
+	}
+
+	ret = __do_fault(vmf);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		goto uncharge_out;
+	if (ret & VM_FAULT_DONE_COW)
+		return ret;
+
+	copy_user_highpage(vmf->cow_page, vmf->page, vmf->address, vma);
+	__SetPageUptodate(vmf->cow_page);
+
+	ret |= finish_fault(vmf);
+	unlock_page(vmf->page);
+	put_page(vmf->page);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		goto uncharge_out;
+	return ret;
+uncharge_out:
+	mem_cgroup_cancel_charge(vmf->cow_page, vmf->memcg, false);
+	put_page(vmf->cow_page);
+	return ret;
+}
+
+static vm_fault_t do_shared_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	vm_fault_t ret, tmp;
+
+	ret = __do_fault(vmf);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
+		return ret;
+
+	/*
+	 * Check if the backing address space wants to know that the page is
+	 * about to become writable
+	 */
+	if (vma->vm_ops->page_mkwrite) {
+		unlock_page(vmf->page);
+		tmp = do_page_mkwrite(vmf);
+		if (unlikely(!tmp ||
+				(tmp & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
+			put_page(vmf->page);
+			return tmp;
+		}
+	}
+
+	ret |= finish_fault(vmf);
+	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
+					VM_FAULT_RETRY))) {
+		unlock_page(vmf->page);
+		put_page(vmf->page);
+		return ret;
+	}
+
+	fault_dirty_shared_page(vma, vmf->page);
+	return ret;
+}
+
+/*
+ * We enter with non-exclusive mmap_sem (to exclude vma changes,
+ * but allow concurrent faults).
+ * The mmap_sem may have been released depending on flags and our
+ * return value.  See filemap_fault() and __lock_page_or_retry().
+ * If mmap_sem is released, vma may become invalid (for example
+ * by other thread calling munmap()).
+ */
+static vm_fault_t do_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct mm_struct *vm_mm = vma->vm_mm;
+	vm_fault_t ret;
+
+	/*
+	 * The VMA was not fully populated on mmap() or missing VM_DONTEXPAND
+	 */
+	if (!vma->vm_ops->fault) {
+		/*
+		 * If we find a migration pmd entry or a none pmd entry, which
+		 * should never happen, return SIGBUS
+		 */
+		if (unlikely(!pmd_present(*vmf->pmd)))
+			ret = VM_FAULT_SIGBUS;
+		else {
+			vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm,
+						       vmf->pmd,
+						       vmf->address,
+						       &vmf->ptl);
+			/*
+			 * Make sure this is not a temporary clearing of pte
+			 * by holding ptl and checking again. A R/M/W update
+			 * of pte involves: take ptl, clearing the pte so that
+			 * we don't have concurrent modification by hardware
+			 * followed by an update.
+			 */
+			if (unlikely(pte_none(*vmf->pte)))
+				ret = VM_FAULT_SIGBUS;
+			else
+				ret = VM_FAULT_NOPAGE;
+
+			pte_unmap_unlock(vmf->pte, vmf->ptl);
+		}
+	} else if (!(vmf->flags & FAULT_FLAG_WRITE))
+		ret = do_read_fault(vmf);
+	else if (!(vma->vm_flags & VM_SHARED))
+		ret = do_cow_fault(vmf);
+	else
+		ret = do_shared_fault(vmf);
+
+	/* preallocated pagetable is unused: free it */
+	if (vmf->prealloc_pte) {
+		pte_free(vm_mm, vmf->prealloc_pte);
+		vmf->prealloc_pte = NULL;
+	}
+	return ret;
+}
+
+static int numa_migrate_prep(struct page *page, struct vm_area_struct *vma,
+				unsigned long addr, int page_nid,
+				int *flags)
+{
+	get_page(page);
+
+	count_vm_numa_event(NUMA_HINT_FAULTS);
+	if (page_nid == numa_node_id()) {
+		count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
+		*flags |= TNF_FAULT_LOCAL;
+	}
+
+	return mpol_misplaced(page, vma, addr);
+}
+
+static vm_fault_t do_numa_page(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct page *page = NULL;
+	int page_nid = -1;
+	int last_cpupid;
+	int target_nid;
+	bool migrated = false;
+	pte_t pte;
+	bool was_writable = pte_savedwrite(vmf->orig_pte);
+	int flags = 0;
+
+	/*
+	 * The "pte" at this point cannot be used safely without
+	 * validation through pte_unmap_same(). It's of NUMA type but
+	 * the pfn may be screwed if the read is non atomic.
+	 */
+	vmf->ptl = pte_lockptr(vma->vm_mm, vmf->pmd);
+	spin_lock(vmf->ptl);
+	if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) {
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		goto out;
+	}
+
+	/*
+	 * Make it present again, Depending on how arch implementes non
+	 * accessible ptes, some can allow access by kernel mode.
+	 */
+	pte = ptep_modify_prot_start(vma->vm_mm, vmf->address, vmf->pte);
+	pte = pte_modify(pte, vma->vm_page_prot);
+	pte = pte_mkyoung(pte);
+	if (was_writable)
+		pte = pte_mkwrite(pte);
+	ptep_modify_prot_commit(vma->vm_mm, vmf->address, vmf->pte, pte);
+	update_mmu_cache(vma, vmf->address, vmf->pte);
+
+	page = vm_normal_page(vma, vmf->address, pte);
+	if (!page) {
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		return 0;
+	}
+
+	/* TODO: handle PTE-mapped THP */
+	if (PageCompound(page)) {
+		pte_unmap_unlock(vmf->pte, vmf->ptl);
+		return 0;
+	}
+
+	/*
+	 * Avoid grouping on RO pages in general. RO pages shouldn't hurt as
+	 * much anyway since they can be in shared cache state. This misses
+	 * the case where a mapping is writable but the process never writes
+	 * to it but pte_write gets cleared during protection updates and
+	 * pte_dirty has unpredictable behaviour between PTE scan updates,
+	 * background writeback, dirty balancing and application behaviour.
+	 */
+	if (!pte_write(pte))
+		flags |= TNF_NO_GROUP;
+
+	/*
+	 * Flag if the page is shared between multiple address spaces. This
+	 * is later used when determining whether to group tasks together
+	 */
+	if (page_mapcount(page) > 1 && (vma->vm_flags & VM_SHARED))
+		flags |= TNF_SHARED;
+
+	last_cpupid = page_cpupid_last(page);
+	page_nid = page_to_nid(page);
+	target_nid = numa_migrate_prep(page, vma, vmf->address, page_nid,
+			&flags);
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	if (target_nid == -1) {
+		put_page(page);
+		goto out;
+	}
+
+	/* Migrate to the requested node */
+	migrated = migrate_misplaced_page(page, vma, target_nid);
+	if (migrated) {
+		page_nid = target_nid;
+		flags |= TNF_MIGRATED;
+	} else
+		flags |= TNF_MIGRATE_FAIL;
+
+out:
+	if (page_nid != -1)
+		task_numa_fault(last_cpupid, page_nid, 1, flags);
+	return 0;
+}
+
+static inline vm_fault_t create_huge_pmd(struct vm_fault *vmf)
+{
+	if (vma_is_anonymous(vmf->vma))
+		return do_huge_pmd_anonymous_page(vmf);
+	if (vmf->vma->vm_ops->huge_fault)
+		return vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PMD);
+	return VM_FAULT_FALLBACK;
+}
+
+/* `inline' is required to avoid gcc 4.1.2 build error */
+static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf, pmd_t orig_pmd)
+{
+	if (vma_is_anonymous(vmf->vma))
+		return do_huge_pmd_wp_page(vmf, orig_pmd);
+	if (vmf->vma->vm_ops->huge_fault)
+		return vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PMD);
+
+	/* COW handled on pte level: split pmd */
+	VM_BUG_ON_VMA(vmf->vma->vm_flags & VM_SHARED, vmf->vma);
+	__split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL);
+
+	return VM_FAULT_FALLBACK;
+}
+
+static inline bool vma_is_accessible(struct vm_area_struct *vma)
+{
+	return vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE);
+}
+
+static vm_fault_t create_huge_pud(struct vm_fault *vmf)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	/* No support for anonymous transparent PUD pages yet */
+	if (vma_is_anonymous(vmf->vma))
+		return VM_FAULT_FALLBACK;
+	if (vmf->vma->vm_ops->huge_fault)
+		return vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PUD);
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+	return VM_FAULT_FALLBACK;
+}
+
+static vm_fault_t wp_huge_pud(struct vm_fault *vmf, pud_t orig_pud)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	/* No support for anonymous transparent PUD pages yet */
+	if (vma_is_anonymous(vmf->vma))
+		return VM_FAULT_FALLBACK;
+	if (vmf->vma->vm_ops->huge_fault)
+		return vmf->vma->vm_ops->huge_fault(vmf, PE_SIZE_PUD);
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+	return VM_FAULT_FALLBACK;
+}
+
+/*
+ * These routines also need to handle stuff like marking pages dirty
+ * and/or accessed for architectures that don't do it in hardware (most
+ * RISC architectures).  The early dirtying is also good on the i386.
+ *
+ * There is also a hook called "update_mmu_cache()" that architectures
+ * with external mmu caches can use to update those (ie the Sparc or
+ * PowerPC hashed page tables that act as extended TLBs).
+ *
+ * We enter with non-exclusive mmap_sem (to exclude vma changes, but allow
+ * concurrent faults).
+ *
+ * The mmap_sem may have been released depending on flags and our return value.
+ * See filemap_fault() and __lock_page_or_retry().
+ */
+static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
+{
+	pte_t entry;
+
+	if (unlikely(pmd_none(*vmf->pmd))) {
+		/*
+		 * Leave __pte_alloc() until later: because vm_ops->fault may
+		 * want to allocate huge page, and if we expose page table
+		 * for an instant, it will be difficult to retract from
+		 * concurrent faults and from rmap lookups.
+		 */
+		vmf->pte = NULL;
+	} else {
+		/* See comment in pte_alloc_one_map() */
+		if (pmd_devmap_trans_unstable(vmf->pmd))
+			return 0;
+		/*
+		 * A regular pmd is established and it can't morph into a huge
+		 * pmd from under us anymore at this point because we hold the
+		 * mmap_sem read mode and khugepaged takes it in write mode.
+		 * So now it's safe to run pte_offset_map().
+		 */
+		vmf->pte = pte_offset_map(vmf->pmd, vmf->address);
+		vmf->orig_pte = *vmf->pte;
+
+		/*
+		 * some architectures can have larger ptes than wordsize,
+		 * e.g.ppc44x-defconfig has CONFIG_PTE_64BIT=y and
+		 * CONFIG_32BIT=y, so READ_ONCE cannot guarantee atomic
+		 * accesses.  The code below just needs a consistent view
+		 * for the ifs and we later double check anyway with the
+		 * ptl lock held. So here a barrier will do.
+		 */
+		barrier();
+		if (pte_none(vmf->orig_pte)) {
+			pte_unmap(vmf->pte);
+			vmf->pte = NULL;
+		}
+	}
+
+	if (!vmf->pte) {
+		if (vma_is_anonymous(vmf->vma))
+			return do_anonymous_page(vmf);
+		else
+			return do_fault(vmf);
+	}
+
+	if (!pte_present(vmf->orig_pte))
+		return do_swap_page(vmf);
+
+	if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma))
+		return do_numa_page(vmf);
+
+	vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
+	spin_lock(vmf->ptl);
+	entry = vmf->orig_pte;
+	if (unlikely(!pte_same(*vmf->pte, entry)))
+		goto unlock;
+	if (vmf->flags & FAULT_FLAG_WRITE) {
+		if (!pte_write(entry))
+			return do_wp_page(vmf);
+		entry = pte_mkdirty(entry);
+	}
+	entry = pte_mkyoung(entry);
+	if (ptep_set_access_flags(vmf->vma, vmf->address, vmf->pte, entry,
+				vmf->flags & FAULT_FLAG_WRITE)) {
+		update_mmu_cache(vmf->vma, vmf->address, vmf->pte);
+	} else {
+		/*
+		 * This is needed only for protection faults but the arch code
+		 * is not yet telling us if this is a protection fault or not.
+		 * This still avoids useless tlb flushes for .text page faults
+		 * with threads.
+		 */
+		if (vmf->flags & FAULT_FLAG_WRITE)
+			flush_tlb_fix_spurious_fault(vmf->vma, vmf->address);
+	}
+unlock:
+	pte_unmap_unlock(vmf->pte, vmf->ptl);
+	return 0;
+}
+
+/*
+ * By the time we get here, we already hold the mm semaphore
+ *
+ * The mmap_sem may have been released depending on flags and our
+ * return value.  See filemap_fault() and __lock_page_or_retry().
+ */
+static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
+		unsigned long address, unsigned int flags)
+{
+	struct vm_fault vmf = {
+		.vma = vma,
+		.address = address & PAGE_MASK,
+		.flags = flags,
+		.pgoff = linear_page_index(vma, address),
+		.gfp_mask = __get_fault_gfp_mask(vma),
+	};
+	unsigned int dirty = flags & FAULT_FLAG_WRITE;
+	struct mm_struct *mm = vma->vm_mm;
+	pgd_t *pgd;
+	p4d_t *p4d;
+	vm_fault_t ret;
+
+	pgd = pgd_offset(mm, address);
+	p4d = p4d_alloc(mm, pgd, address);
+	if (!p4d)
+		return VM_FAULT_OOM;
+
+	vmf.pud = pud_alloc(mm, p4d, address);
+	if (!vmf.pud)
+		return VM_FAULT_OOM;
+	if (pud_none(*vmf.pud) && __transparent_hugepage_enabled(vma)) {
+		ret = create_huge_pud(&vmf);
+		if (!(ret & VM_FAULT_FALLBACK))
+			return ret;
+	} else {
+		pud_t orig_pud = *vmf.pud;
+
+		barrier();
+		if (pud_trans_huge(orig_pud) || pud_devmap(orig_pud)) {
+
+			/* NUMA case for anonymous PUDs would go here */
+
+			if (dirty && !pud_write(orig_pud)) {
+				ret = wp_huge_pud(&vmf, orig_pud);
+				if (!(ret & VM_FAULT_FALLBACK))
+					return ret;
+			} else {
+				huge_pud_set_accessed(&vmf, orig_pud);
+				return 0;
+			}
+		}
+	}
+
+	vmf.pmd = pmd_alloc(mm, vmf.pud, address);
+	if (!vmf.pmd)
+		return VM_FAULT_OOM;
+	if (pmd_none(*vmf.pmd) && __transparent_hugepage_enabled(vma)) {
+		ret = create_huge_pmd(&vmf);
+		if (!(ret & VM_FAULT_FALLBACK))
+			return ret;
+	} else {
+		pmd_t orig_pmd = *vmf.pmd;
+
+		barrier();
+		if (unlikely(is_swap_pmd(orig_pmd))) {
+			VM_BUG_ON(thp_migration_supported() &&
+					  !is_pmd_migration_entry(orig_pmd));
+			if (is_pmd_migration_entry(orig_pmd))
+				pmd_migration_entry_wait(mm, vmf.pmd);
+			return 0;
+		}
+		if (pmd_trans_huge(orig_pmd) || pmd_devmap(orig_pmd)) {
+			if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
+				return do_huge_pmd_numa_page(&vmf, orig_pmd);
+
+			if (dirty && !pmd_write(orig_pmd)) {
+				ret = wp_huge_pmd(&vmf, orig_pmd);
+				if (!(ret & VM_FAULT_FALLBACK))
+					return ret;
+			} else {
+				huge_pmd_set_accessed(&vmf, orig_pmd);
+				return 0;
+			}
+		}
+	}
+
+	return handle_pte_fault(&vmf);
+}
+
+/*
+ * By the time we get here, we already hold the mm semaphore
+ *
+ * The mmap_sem may have been released depending on flags and our
+ * return value.  See filemap_fault() and __lock_page_or_retry().
+ */
+vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
+		unsigned int flags)
+{
+	vm_fault_t ret;
+
+	__set_current_state(TASK_RUNNING);
+
+	count_vm_event(PGFAULT);
+	count_memcg_event_mm(vma->vm_mm, PGFAULT);
+
+	/* do counter updates before entering really critical section. */
+	check_sync_rss_stat(current);
+
+	if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
+					    flags & FAULT_FLAG_INSTRUCTION,
+					    flags & FAULT_FLAG_REMOTE))
+		return VM_FAULT_SIGSEGV;
+
+	/*
+	 * Enable the memcg OOM handling for faults triggered in user
+	 * space.  Kernel faults are handled more gracefully.
+	 */
+	if (flags & FAULT_FLAG_USER)
+		mem_cgroup_enter_user_fault();
+
+	if (unlikely(is_vm_hugetlb_page(vma)))
+		ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
+	else
+		ret = __handle_mm_fault(vma, address, flags);
+
+	if (flags & FAULT_FLAG_USER) {
+		mem_cgroup_exit_user_fault();
+		/*
+		 * The task may have entered a memcg OOM situation but
+		 * if the allocation error was handled gracefully (no
+		 * VM_FAULT_OOM), there is no need to kill anything.
+		 * Just clean up the OOM state peacefully.
+		 */
+		if (task_in_memcg_oom(current) && !(ret & VM_FAULT_OOM))
+			mem_cgroup_oom_synchronize(false);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(handle_mm_fault);
+
+#ifndef __PAGETABLE_P4D_FOLDED
+/*
+ * Allocate p4d page table.
+ * We've already handled the fast-path in-line.
+ */
+int __p4d_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
+{
+	p4d_t *new = p4d_alloc_one(mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	smp_wmb(); /* See comment in __pte_alloc */
+
+	spin_lock(&mm->page_table_lock);
+	if (pgd_present(*pgd))		/* Another has populated it */
+		p4d_free(mm, new);
+	else
+		pgd_populate(mm, pgd, new);
+	spin_unlock(&mm->page_table_lock);
+	return 0;
+}
+#endif /* __PAGETABLE_P4D_FOLDED */
+
+#ifndef __PAGETABLE_PUD_FOLDED
+/*
+ * Allocate page upper directory.
+ * We've already handled the fast-path in-line.
+ */
+int __pud_alloc(struct mm_struct *mm, p4d_t *p4d, unsigned long address)
+{
+	pud_t *new = pud_alloc_one(mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	smp_wmb(); /* See comment in __pte_alloc */
+
+	spin_lock(&mm->page_table_lock);
+#ifndef __ARCH_HAS_5LEVEL_HACK
+	if (!p4d_present(*p4d)) {
+		mm_inc_nr_puds(mm);
+		p4d_populate(mm, p4d, new);
+	} else	/* Another has populated it */
+		pud_free(mm, new);
+#else
+	if (!pgd_present(*p4d)) {
+		mm_inc_nr_puds(mm);
+		pgd_populate(mm, p4d, new);
+	} else	/* Another has populated it */
+		pud_free(mm, new);
+#endif /* __ARCH_HAS_5LEVEL_HACK */
+	spin_unlock(&mm->page_table_lock);
+	return 0;
+}
+#endif /* __PAGETABLE_PUD_FOLDED */
+
+#ifndef __PAGETABLE_PMD_FOLDED
+/*
+ * Allocate page middle directory.
+ * We've already handled the fast-path in-line.
+ */
+int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
+{
+	spinlock_t *ptl;
+	pmd_t *new = pmd_alloc_one(mm, address);
+	if (!new)
+		return -ENOMEM;
+
+	smp_wmb(); /* See comment in __pte_alloc */
+
+	ptl = pud_lock(mm, pud);
+#ifndef __ARCH_HAS_4LEVEL_HACK
+	if (!pud_present(*pud)) {
+		mm_inc_nr_pmds(mm);
+		pud_populate(mm, pud, new);
+	} else	/* Another has populated it */
+		pmd_free(mm, new);
+#else
+	if (!pgd_present(*pud)) {
+		mm_inc_nr_pmds(mm);
+		pgd_populate(mm, pud, new);
+	} else /* Another has populated it */
+		pmd_free(mm, new);
+#endif /* __ARCH_HAS_4LEVEL_HACK */
+	spin_unlock(ptl);
+	return 0;
+}
+#endif /* __PAGETABLE_PMD_FOLDED */
+
+static int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+			    unsigned long *start, unsigned long *end,
+			    pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *ptep;
+
+	pgd = pgd_offset(mm, address);
+	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+		goto out;
+
+	p4d = p4d_offset(pgd, address);
+	if (p4d_none(*p4d) || unlikely(p4d_bad(*p4d)))
+		goto out;
+
+	pud = pud_offset(p4d, address);
+	if (pud_none(*pud) || unlikely(pud_bad(*pud)))
+		goto out;
+
+	pmd = pmd_offset(pud, address);
+	VM_BUG_ON(pmd_trans_huge(*pmd));
+
+	if (pmd_huge(*pmd)) {
+		if (!pmdpp)
+			goto out;
+
+		if (start && end) {
+			*start = address & PMD_MASK;
+			*end = *start + PMD_SIZE;
+			mmu_notifier_invalidate_range_start(mm, *start, *end);
+		}
+		*ptlp = pmd_lock(mm, pmd);
+		if (pmd_huge(*pmd)) {
+			*pmdpp = pmd;
+			return 0;
+		}
+		spin_unlock(*ptlp);
+		if (start && end)
+			mmu_notifier_invalidate_range_end(mm, *start, *end);
+	}
+
+	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+		goto out;
+
+	if (start && end) {
+		*start = address & PAGE_MASK;
+		*end = *start + PAGE_SIZE;
+		mmu_notifier_invalidate_range_start(mm, *start, *end);
+	}
+	ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
+	if (!pte_present(*ptep))
+		goto unlock;
+	*ptepp = ptep;
+	return 0;
+unlock:
+	pte_unmap_unlock(ptep, *ptlp);
+	if (start && end)
+		mmu_notifier_invalidate_range_end(mm, *start, *end);
+out:
+	return -EINVAL;
+}
+
+static inline int follow_pte(struct mm_struct *mm, unsigned long address,
+			     pte_t **ptepp, spinlock_t **ptlp)
+{
+	int res;
+
+	/* (void) is needed to make gcc happy */
+	(void) __cond_lock(*ptlp,
+			   !(res = __follow_pte_pmd(mm, address, NULL, NULL,
+						    ptepp, NULL, ptlp)));
+	return res;
+}
+
+int follow_pte_pmd(struct mm_struct *mm, unsigned long address,
+			     unsigned long *start, unsigned long *end,
+			     pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp)
+{
+	int res;
+
+	/* (void) is needed to make gcc happy */
+	(void) __cond_lock(*ptlp,
+			   !(res = __follow_pte_pmd(mm, address, start, end,
+						    ptepp, pmdpp, ptlp)));
+	return res;
+}
+EXPORT_SYMBOL(follow_pte_pmd);
+
+/**
+ * follow_pfn - look up PFN at a user virtual address
+ * @vma: memory mapping
+ * @address: user virtual address
+ * @pfn: location to store found PFN
+ *
+ * Only IO mappings and raw PFN mappings are allowed.
+ *
+ * Returns zero and the pfn at @pfn on success, -ve otherwise.
+ */
+int follow_pfn(struct vm_area_struct *vma, unsigned long address,
+	unsigned long *pfn)
+{
+	int ret = -EINVAL;
+	spinlock_t *ptl;
+	pte_t *ptep;
+
+	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
+		return ret;
+
+	ret = follow_pte(vma->vm_mm, address, &ptep, &ptl);
+	if (ret)
+		return ret;
+	*pfn = pte_pfn(*ptep);
+	pte_unmap_unlock(ptep, ptl);
+	return 0;
+}
+EXPORT_SYMBOL(follow_pfn);
+
+#ifdef CONFIG_HAVE_IOREMAP_PROT
+int follow_phys(struct vm_area_struct *vma,
+		unsigned long address, unsigned int flags,
+		unsigned long *prot, resource_size_t *phys)
+{
+	int ret = -EINVAL;
+	pte_t *ptep, pte;
+	spinlock_t *ptl;
+
+	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
+		goto out;
+
+	if (follow_pte(vma->vm_mm, address, &ptep, &ptl))
+		goto out;
+	pte = *ptep;
+
+	if ((flags & FOLL_WRITE) && !pte_write(pte))
+		goto unlock;
+
+	*prot = pgprot_val(pte_pgprot(pte));
+	*phys = (resource_size_t)pte_pfn(pte) << PAGE_SHIFT;
+
+	ret = 0;
+unlock:
+	pte_unmap_unlock(ptep, ptl);
+out:
+	return ret;
+}
+
+int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
+			void *buf, int len, int write)
+{
+	resource_size_t phys_addr;
+	unsigned long prot = 0;
+	void __iomem *maddr;
+	int offset = addr & (PAGE_SIZE-1);
+
+	if (follow_phys(vma, addr, write, &prot, &phys_addr))
+		return -EINVAL;
+
+	maddr = ioremap_prot(phys_addr, PAGE_ALIGN(len + offset), prot);
+	if (!maddr)
+		return -ENOMEM;
+
+	if (write)
+		memcpy_toio(maddr + offset, buf, len);
+	else
+		memcpy_fromio(buf, maddr + offset, len);
+	iounmap(maddr);
+
+	return len;
+}
+EXPORT_SYMBOL_GPL(generic_access_phys);
+#endif
+
+/*
+ * Access another process' address space as given in mm.  If non-NULL, use the
+ * given task for page fault accounting.
+ */
+int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
+		unsigned long addr, void *buf, int len, unsigned int gup_flags)
+{
+	struct vm_area_struct *vma;
+	void *old_buf = buf;
+	int write = gup_flags & FOLL_WRITE;
+
+	if (down_read_killable(&mm->mmap_sem))
+		return 0;
+
+	/* ignore errors, just check how much was successfully transferred */
+	while (len) {
+		int bytes, ret, offset;
+		void *maddr;
+		struct page *page = NULL;
+
+		ret = get_user_pages_remote(tsk, mm, addr, 1,
+				gup_flags, &page, &vma, NULL);
+		if (ret <= 0) {
+#ifndef CONFIG_HAVE_IOREMAP_PROT
+			break;
+#else
+			/*
+			 * Check if this is a VM_IO | VM_PFNMAP VMA, which
+			 * we can access using slightly different code.
+			 */
+			vma = find_vma(mm, addr);
+			if (!vma || vma->vm_start > addr)
+				break;
+			if (vma->vm_ops && vma->vm_ops->access)
+				ret = vma->vm_ops->access(vma, addr, buf,
+							  len, write);
+			if (ret <= 0)
+				break;
+			bytes = ret;
+#endif
+		} else {
+			bytes = len;
+			offset = addr & (PAGE_SIZE-1);
+			if (bytes > PAGE_SIZE-offset)
+				bytes = PAGE_SIZE-offset;
+
+			maddr = kmap(page);
+			if (write) {
+				copy_to_user_page(vma, page, addr,
+						  maddr + offset, buf, bytes);
+				set_page_dirty_lock(page);
+			} else {
+				copy_from_user_page(vma, page, addr,
+						    buf, maddr + offset, bytes);
+			}
+			kunmap(page);
+			put_page(page);
+		}
+		len -= bytes;
+		buf += bytes;
+		addr += bytes;
+	}
+	up_read(&mm->mmap_sem);
+
+	return buf - old_buf;
+}
+
+/**
+ * access_remote_vm - access another process' address space
+ * @mm:		the mm_struct of the target address space
+ * @addr:	start address to access
+ * @buf:	source or destination buffer
+ * @len:	number of bytes to transfer
+ * @gup_flags:	flags modifying lookup behaviour
+ *
+ * The caller must hold a reference on @mm.
+ */
+int access_remote_vm(struct mm_struct *mm, unsigned long addr,
+		void *buf, int len, unsigned int gup_flags)
+{
+	return __access_remote_vm(NULL, mm, addr, buf, len, gup_flags);
+}
+
+/*
+ * Access another process' address space.
+ * Source/target buffer must be kernel space,
+ * Do not walk the page table directly, use get_user_pages
+ */
+int access_process_vm(struct task_struct *tsk, unsigned long addr,
+		void *buf, int len, unsigned int gup_flags)
+{
+	struct mm_struct *mm;
+	int ret;
+
+	mm = get_task_mm(tsk);
+	if (!mm)
+		return 0;
+
+	ret = __access_remote_vm(tsk, mm, addr, buf, len, gup_flags);
+
+	mmput(mm);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(access_process_vm);
+
+/*
+ * Print the name of a VMA.
+ */
+void print_vma_addr(char *prefix, unsigned long ip)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+
+	/*
+	 * we might be running from an atomic context so we cannot sleep
+	 */
+	if (!down_read_trylock(&mm->mmap_sem))
+		return;
+
+	vma = find_vma(mm, ip);
+	if (vma && vma->vm_file) {
+		struct file *f = vma->vm_file;
+		char *buf = (char *)__get_free_page(GFP_NOWAIT);
+		if (buf) {
+			char *p;
+
+			p = file_path(f, buf, PAGE_SIZE);
+			if (IS_ERR(p))
+				p = "?";
+			printk("%s%s[%lx+%lx]", prefix, kbasename(p),
+					vma->vm_start,
+					vma->vm_end - vma->vm_start);
+			free_page((unsigned long)buf);
+		}
+	}
+	up_read(&mm->mmap_sem);
+}
+
+#if defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP)
+void __might_fault(const char *file, int line)
+{
+	/*
+	 * Some code (nfs/sunrpc) uses socket ops on kernel memory while
+	 * holding the mmap_sem, this is safe because kernel memory doesn't
+	 * get paged out, therefore we'll never actually fault, and the
+	 * below annotations will generate false positives.
+	 */
+	if (uaccess_kernel())
+		return;
+	if (pagefault_disabled())
+		return;
+	__might_sleep(file, line, 0);
+#if defined(CONFIG_DEBUG_ATOMIC_SLEEP)
+	if (current->mm)
+		might_lock_read(&current->mm->mmap_sem);
+#endif
+}
+EXPORT_SYMBOL(__might_fault);
+#endif
+
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
+/*
+ * Process all subpages of the specified huge page with the specified
+ * operation.  The target subpage will be processed last to keep its
+ * cache lines hot.
+ */
+static inline void process_huge_page(
+	unsigned long addr_hint, unsigned int pages_per_huge_page,
+	void (*process_subpage)(unsigned long addr, int idx, void *arg),
+	void *arg)
+{
+	int i, n, base, l;
+	unsigned long addr = addr_hint &
+		~(((unsigned long)pages_per_huge_page << PAGE_SHIFT) - 1);
+
+	/* Process target subpage last to keep its cache lines hot */
+	might_sleep();
+	n = (addr_hint - addr) / PAGE_SIZE;
+	if (2 * n <= pages_per_huge_page) {
+		/* If target subpage in first half of huge page */
+		base = 0;
+		l = n;
+		/* Process subpages at the end of huge page */
+		for (i = pages_per_huge_page - 1; i >= 2 * n; i--) {
+			cond_resched();
+			process_subpage(addr + i * PAGE_SIZE, i, arg);
+		}
+	} else {
+		/* If target subpage in second half of huge page */
+		base = pages_per_huge_page - 2 * (pages_per_huge_page - n);
+		l = pages_per_huge_page - n;
+		/* Process subpages at the begin of huge page */
+		for (i = 0; i < base; i++) {
+			cond_resched();
+			process_subpage(addr + i * PAGE_SIZE, i, arg);
+		}
+	}
+	/*
+	 * Process remaining subpages in left-right-left-right pattern
+	 * towards the target subpage
+	 */
+	for (i = 0; i < l; i++) {
+		int left_idx = base + i;
+		int right_idx = base + 2 * l - 1 - i;
+
+		cond_resched();
+		process_subpage(addr + left_idx * PAGE_SIZE, left_idx, arg);
+		cond_resched();
+		process_subpage(addr + right_idx * PAGE_SIZE, right_idx, arg);
+	}
+}
+
+static void clear_gigantic_page(struct page *page,
+				unsigned long addr,
+				unsigned int pages_per_huge_page)
+{
+	int i;
+	struct page *p = page;
+
+	might_sleep();
+	for (i = 0; i < pages_per_huge_page;
+	     i++, p = mem_map_next(p, page, i)) {
+		cond_resched();
+		clear_user_highpage(p, addr + i * PAGE_SIZE);
+	}
+}
+
+static void clear_subpage(unsigned long addr, int idx, void *arg)
+{
+	struct page *page = arg;
+
+	clear_user_highpage(page + idx, addr);
+}
+
+void clear_huge_page(struct page *page,
+		     unsigned long addr_hint, unsigned int pages_per_huge_page)
+{
+	unsigned long addr = addr_hint &
+		~(((unsigned long)pages_per_huge_page << PAGE_SHIFT) - 1);
+
+	if (unlikely(pages_per_huge_page > MAX_ORDER_NR_PAGES)) {
+		clear_gigantic_page(page, addr, pages_per_huge_page);
+		return;
+	}
+
+	process_huge_page(addr_hint, pages_per_huge_page, clear_subpage, page);
+}
+
+static void copy_user_gigantic_page(struct page *dst, struct page *src,
+				    unsigned long addr,
+				    struct vm_area_struct *vma,
+				    unsigned int pages_per_huge_page)
+{
+	int i;
+	struct page *dst_base = dst;
+	struct page *src_base = src;
+
+	for (i = 0; i < pages_per_huge_page; ) {
+		cond_resched();
+		copy_user_highpage(dst, src, addr + i*PAGE_SIZE, vma);
+
+		i++;
+		dst = mem_map_next(dst, dst_base, i);
+		src = mem_map_next(src, src_base, i);
+	}
+}
+
+struct copy_subpage_arg {
+	struct page *dst;
+	struct page *src;
+	struct vm_area_struct *vma;
+};
+
+static void copy_subpage(unsigned long addr, int idx, void *arg)
+{
+	struct copy_subpage_arg *copy_arg = arg;
+
+	copy_user_highpage(copy_arg->dst + idx, copy_arg->src + idx,
+			   addr, copy_arg->vma);
+}
+
+void copy_user_huge_page(struct page *dst, struct page *src,
+			 unsigned long addr_hint, struct vm_area_struct *vma,
+			 unsigned int pages_per_huge_page)
+{
+	unsigned long addr = addr_hint &
+		~(((unsigned long)pages_per_huge_page << PAGE_SHIFT) - 1);
+	struct copy_subpage_arg arg = {
+		.dst = dst,
+		.src = src,
+		.vma = vma,
+	};
+
+	if (unlikely(pages_per_huge_page > MAX_ORDER_NR_PAGES)) {
+		copy_user_gigantic_page(dst, src, addr, vma,
+					pages_per_huge_page);
+		return;
+	}
+
+	process_huge_page(addr_hint, pages_per_huge_page, copy_subpage, &arg);
+}
+
+long copy_huge_page_from_user(struct page *dst_page,
+				const void __user *usr_src,
+				unsigned int pages_per_huge_page,
+				bool allow_pagefault)
+{
+	void *src = (void *)usr_src;
+	void *page_kaddr;
+	unsigned long i, rc = 0;
+	unsigned long ret_val = pages_per_huge_page * PAGE_SIZE;
+	struct page *subpage = dst_page;
+
+	for (i = 0; i < pages_per_huge_page;
+	     i++, subpage = mem_map_next(subpage, dst_page, i)) {
+		if (allow_pagefault)
+			page_kaddr = kmap(subpage);
+		else
+			page_kaddr = kmap_atomic(subpage);
+		rc = copy_from_user(page_kaddr,
+				(const void __user *)(src + i * PAGE_SIZE),
+				PAGE_SIZE);
+		if (allow_pagefault)
+			kunmap(subpage);
+		else
+			kunmap_atomic(page_kaddr);
+
+		ret_val -= (PAGE_SIZE - rc);
+		if (rc)
+			break;
+
+		flush_dcache_page(subpage);
+
+		cond_resched();
+	}
+	return ret_val;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
+
+#if USE_SPLIT_PTE_PTLOCKS && ALLOC_SPLIT_PTLOCKS
+
+static struct kmem_cache *page_ptl_cachep;
+
+void __init ptlock_cache_init(void)
+{
+	page_ptl_cachep = kmem_cache_create("page->ptl", sizeof(spinlock_t), 0,
+			SLAB_PANIC, NULL);
+}
+
+bool ptlock_alloc(struct page *page)
+{
+	spinlock_t *ptl;
+
+	ptl = kmem_cache_alloc(page_ptl_cachep, GFP_KERNEL);
+	if (!ptl)
+		return false;
+	page->ptl = ptl;
+	return true;
+}
+
+void ptlock_free(struct page *page)
+{
+	kmem_cache_free(page_ptl_cachep, page->ptl);
+}
+#endif