Adding upstream version 5.10.209.upstream/5.10.209

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

1 files changed, 1936 insertions, 0 deletions

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
new file mode 100644
index 000000000..f320ff02c
--- /dev/null
+++ b/mm/memory-failure.c
@@ -0,0 +1,1936 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2008, 2009 Intel Corporation
+ * Authors: Andi Kleen, Fengguang Wu
+ *
+ * High level machine check handler. Handles pages reported by the
+ * hardware as being corrupted usually due to a multi-bit ECC memory or cache
+ * failure.
+ * 
+ * In addition there is a "soft offline" entry point that allows stop using
+ * not-yet-corrupted-by-suspicious pages without killing anything.
+ *
+ * Handles page cache pages in various states.	The tricky part
+ * here is that we can access any page asynchronously in respect to 
+ * other VM users, because memory failures could happen anytime and 
+ * anywhere. This could violate some of their assumptions. This is why 
+ * this code has to be extremely careful. Generally it tries to use 
+ * normal locking rules, as in get the standard locks, even if that means 
+ * the error handling takes potentially a long time.
+ *
+ * It can be very tempting to add handling for obscure cases here.
+ * In general any code for handling new cases should only be added iff:
+ * - You know how to test it.
+ * - You have a test that can be added to mce-test
+ *   https://git.kernel.org/cgit/utils/cpu/mce/mce-test.git/
+ * - The case actually shows up as a frequent (top 10) page state in
+ *   tools/vm/page-types when running a real workload.
+ * 
+ * There are several operations here with exponential complexity because
+ * of unsuitable VM data structures. For example the operation to map back 
+ * from RMAP chains to processes has to walk the complete process list and 
+ * has non linear complexity with the number. But since memory corruptions
+ * are rare we hope to get away with this. This avoids impacting the core 
+ * VM.
+ */
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/page-flags.h>
+#include <linux/kernel-page-flags.h>
+#include <linux/sched/signal.h>
+#include <linux/sched/task.h>
+#include <linux/ksm.h>
+#include <linux/rmap.h>
+#include <linux/export.h>
+#include <linux/pagemap.h>
+#include <linux/swap.h>
+#include <linux/backing-dev.h>
+#include <linux/migrate.h>
+#include <linux/suspend.h>
+#include <linux/slab.h>
+#include <linux/swapops.h>
+#include <linux/hugetlb.h>
+#include <linux/memory_hotplug.h>
+#include <linux/mm_inline.h>
+#include <linux/memremap.h>
+#include <linux/kfifo.h>
+#include <linux/ratelimit.h>
+#include <linux/page-isolation.h>
+#include "internal.h"
+#include "ras/ras_event.h"
+
+int sysctl_memory_failure_early_kill __read_mostly = 0;
+
+int sysctl_memory_failure_recovery __read_mostly = 1;
+
+atomic_long_t num_poisoned_pages __read_mostly = ATOMIC_LONG_INIT(0);
+
+static bool page_handle_poison(struct page *page, bool hugepage_or_freepage, bool release)
+{
+	if (hugepage_or_freepage) {
+		/*
+		 * Doing this check for free pages is also fine since dissolve_free_huge_page
+		 * returns 0 for non-hugetlb pages as well.
+		 */
+		if (dissolve_free_huge_page(page) || !take_page_off_buddy(page))
+			/*
+			 * We could fail to take off the target page from buddy
+			 * for example due to racy page allocaiton, but that's
+			 * acceptable because soft-offlined page is not broken
+			 * and if someone really want to use it, they should
+			 * take it.
+			 */
+			return false;
+	}
+
+	SetPageHWPoison(page);
+	if (release)
+		put_page(page);
+	page_ref_inc(page);
+	num_poisoned_pages_inc();
+
+	return true;
+}
+
+#if defined(CONFIG_HWPOISON_INJECT) || defined(CONFIG_HWPOISON_INJECT_MODULE)
+
+u32 hwpoison_filter_enable = 0;
+u32 hwpoison_filter_dev_major = ~0U;
+u32 hwpoison_filter_dev_minor = ~0U;
+u64 hwpoison_filter_flags_mask;
+u64 hwpoison_filter_flags_value;
+EXPORT_SYMBOL_GPL(hwpoison_filter_enable);
+EXPORT_SYMBOL_GPL(hwpoison_filter_dev_major);
+EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor);
+EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask);
+EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value);
+
+static int hwpoison_filter_dev(struct page *p)
+{
+	struct address_space *mapping;
+	dev_t dev;
+
+	if (hwpoison_filter_dev_major == ~0U &&
+	    hwpoison_filter_dev_minor == ~0U)
+		return 0;
+
+	/*
+	 * page_mapping() does not accept slab pages.
+	 */
+	if (PageSlab(p))
+		return -EINVAL;
+
+	mapping = page_mapping(p);
+	if (mapping == NULL || mapping->host == NULL)
+		return -EINVAL;
+
+	dev = mapping->host->i_sb->s_dev;
+	if (hwpoison_filter_dev_major != ~0U &&
+	    hwpoison_filter_dev_major != MAJOR(dev))
+		return -EINVAL;
+	if (hwpoison_filter_dev_minor != ~0U &&
+	    hwpoison_filter_dev_minor != MINOR(dev))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int hwpoison_filter_flags(struct page *p)
+{
+	if (!hwpoison_filter_flags_mask)
+		return 0;
+
+	if ((stable_page_flags(p) & hwpoison_filter_flags_mask) ==
+				    hwpoison_filter_flags_value)
+		return 0;
+	else
+		return -EINVAL;
+}
+
+/*
+ * This allows stress tests to limit test scope to a collection of tasks
+ * by putting them under some memcg. This prevents killing unrelated/important
+ * processes such as /sbin/init. Note that the target task may share clean
+ * pages with init (eg. libc text), which is harmless. If the target task
+ * share _dirty_ pages with another task B, the test scheme must make sure B
+ * is also included in the memcg. At last, due to race conditions this filter
+ * can only guarantee that the page either belongs to the memcg tasks, or is
+ * a freed page.
+ */
+#ifdef CONFIG_MEMCG
+u64 hwpoison_filter_memcg;
+EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
+static int hwpoison_filter_task(struct page *p)
+{
+	if (!hwpoison_filter_memcg)
+		return 0;
+
+	if (page_cgroup_ino(p) != hwpoison_filter_memcg)
+		return -EINVAL;
+
+	return 0;
+}
+#else
+static int hwpoison_filter_task(struct page *p) { return 0; }
+#endif
+
+int hwpoison_filter(struct page *p)
+{
+	if (!hwpoison_filter_enable)
+		return 0;
+
+	if (hwpoison_filter_dev(p))
+		return -EINVAL;
+
+	if (hwpoison_filter_flags(p))
+		return -EINVAL;
+
+	if (hwpoison_filter_task(p))
+		return -EINVAL;
+
+	return 0;
+}
+#else
+int hwpoison_filter(struct page *p)
+{
+	return 0;
+}
+#endif
+
+EXPORT_SYMBOL_GPL(hwpoison_filter);
+
+/*
+ * Kill all processes that have a poisoned page mapped and then isolate
+ * the page.
+ *
+ * General strategy:
+ * Find all processes having the page mapped and kill them.
+ * But we keep a page reference around so that the page is not
+ * actually freed yet.
+ * Then stash the page away
+ *
+ * There's no convenient way to get back to mapped processes
+ * from the VMAs. So do a brute-force search over all
+ * running processes.
+ *
+ * Remember that machine checks are not common (or rather
+ * if they are common you have other problems), so this shouldn't
+ * be a performance issue.
+ *
+ * Also there are some races possible while we get from the
+ * error detection to actually handle it.
+ */
+
+struct to_kill {
+	struct list_head nd;
+	struct task_struct *tsk;
+	unsigned long addr;
+	short size_shift;
+};
+
+/*
+ * Send all the processes who have the page mapped a signal.
+ * ``action optional'' if they are not immediately affected by the error
+ * ``action required'' if error happened in current execution context
+ */
+static int kill_proc(struct to_kill *tk, unsigned long pfn, int flags)
+{
+	struct task_struct *t = tk->tsk;
+	short addr_lsb = tk->size_shift;
+	int ret = 0;
+
+	pr_err("Memory failure: %#lx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
+			pfn, t->comm, t->pid);
+
+	if (flags & MF_ACTION_REQUIRED) {
+		WARN_ON_ONCE(t != current);
+		ret = force_sig_mceerr(BUS_MCEERR_AR,
+					 (void __user *)tk->addr, addr_lsb);
+	} else {
+		/*
+		 * Don't use force here, it's convenient if the signal
+		 * can be temporarily blocked.
+		 * This could cause a loop when the user sets SIGBUS
+		 * to SIG_IGN, but hopefully no one will do that?
+		 */
+		ret = send_sig_mceerr(BUS_MCEERR_AO, (void __user *)tk->addr,
+				      addr_lsb, t);  /* synchronous? */
+	}
+	if (ret < 0)
+		pr_info("Memory failure: Error sending signal to %s:%d: %d\n",
+			t->comm, t->pid, ret);
+	return ret;
+}
+
+/*
+ * When a unknown page type is encountered drain as many buffers as possible
+ * in the hope to turn the page into a LRU or free page, which we can handle.
+ */
+void shake_page(struct page *p, int access)
+{
+	if (PageHuge(p))
+		return;
+
+	if (!PageSlab(p)) {
+		lru_add_drain_all();
+		if (PageLRU(p))
+			return;
+		drain_all_pages(page_zone(p));
+		if (PageLRU(p) || is_free_buddy_page(p))
+			return;
+	}
+
+	/*
+	 * Only call shrink_node_slabs here (which would also shrink
+	 * other caches) if access is not potentially fatal.
+	 */
+	if (access)
+		drop_slab_node(page_to_nid(p));
+}
+EXPORT_SYMBOL_GPL(shake_page);
+
+static unsigned long dev_pagemap_mapping_shift(struct page *page,
+		struct vm_area_struct *vma)
+{
+	unsigned long address = vma_address(page, vma);
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+
+	pgd = pgd_offset(vma->vm_mm, address);
+	if (!pgd_present(*pgd))
+		return 0;
+	p4d = p4d_offset(pgd, address);
+	if (!p4d_present(*p4d))
+		return 0;
+	pud = pud_offset(p4d, address);
+	if (!pud_present(*pud))
+		return 0;
+	if (pud_devmap(*pud))
+		return PUD_SHIFT;
+	pmd = pmd_offset(pud, address);
+	if (!pmd_present(*pmd))
+		return 0;
+	if (pmd_devmap(*pmd))
+		return PMD_SHIFT;
+	pte = pte_offset_map(pmd, address);
+	if (!pte_present(*pte))
+		return 0;
+	if (pte_devmap(*pte))
+		return PAGE_SHIFT;
+	return 0;
+}
+
+/*
+ * Failure handling: if we can't find or can't kill a process there's
+ * not much we can do.	We just print a message and ignore otherwise.
+ */
+
+/*
+ * Schedule a process for later kill.
+ * Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
+ */
+static void add_to_kill(struct task_struct *tsk, struct page *p,
+		       struct vm_area_struct *vma,
+		       struct list_head *to_kill)
+{
+	struct to_kill *tk;
+
+	tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC);
+	if (!tk) {
+		pr_err("Memory failure: Out of memory while machine check handling\n");
+		return;
+	}
+
+	tk->addr = page_address_in_vma(p, vma);
+	if (is_zone_device_page(p))
+		tk->size_shift = dev_pagemap_mapping_shift(p, vma);
+	else
+		tk->size_shift = page_shift(compound_head(p));
+
+	/*
+	 * Send SIGKILL if "tk->addr == -EFAULT". Also, as
+	 * "tk->size_shift" is always non-zero for !is_zone_device_page(),
+	 * so "tk->size_shift == 0" effectively checks no mapping on
+	 * ZONE_DEVICE. Indeed, when a devdax page is mmapped N times
+	 * to a process' address space, it's possible not all N VMAs
+	 * contain mappings for the page, but at least one VMA does.
+	 * Only deliver SIGBUS with payload derived from the VMA that
+	 * has a mapping for the page.
+	 */
+	if (tk->addr == -EFAULT) {
+		pr_info("Memory failure: Unable to find user space address %lx in %s\n",
+			page_to_pfn(p), tsk->comm);
+	} else if (tk->size_shift == 0) {
+		kfree(tk);
+		return;
+	}
+
+	get_task_struct(tsk);
+	tk->tsk = tsk;
+	list_add_tail(&tk->nd, to_kill);
+}
+
+/*
+ * Kill the processes that have been collected earlier.
+ *
+ * Only do anything when DOIT is set, otherwise just free the list
+ * (this is used for clean pages which do not need killing)
+ * Also when FAIL is set do a force kill because something went
+ * wrong earlier.
+ */
+static void kill_procs(struct list_head *to_kill, int forcekill, bool fail,
+		unsigned long pfn, int flags)
+{
+	struct to_kill *tk, *next;
+
+	list_for_each_entry_safe (tk, next, to_kill, nd) {
+		if (forcekill) {
+			/*
+			 * In case something went wrong with munmapping
+			 * make sure the process doesn't catch the
+			 * signal and then access the memory. Just kill it.
+			 */
+			if (fail || tk->addr == -EFAULT) {
+				pr_err("Memory failure: %#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n",
+				       pfn, tk->tsk->comm, tk->tsk->pid);
+				do_send_sig_info(SIGKILL, SEND_SIG_PRIV,
+						 tk->tsk, PIDTYPE_PID);
+			}
+
+			/*
+			 * In theory the process could have mapped
+			 * something else on the address in-between. We could
+			 * check for that, but we need to tell the
+			 * process anyways.
+			 */
+			else if (kill_proc(tk, pfn, flags) < 0)
+				pr_err("Memory failure: %#lx: Cannot send advisory machine check signal to %s:%d\n",
+				       pfn, tk->tsk->comm, tk->tsk->pid);
+		}
+		put_task_struct(tk->tsk);
+		kfree(tk);
+	}
+}
+
+/*
+ * Find a dedicated thread which is supposed to handle SIGBUS(BUS_MCEERR_AO)
+ * on behalf of the thread group. Return task_struct of the (first found)
+ * dedicated thread if found, and return NULL otherwise.
+ *
+ * We already hold read_lock(&tasklist_lock) in the caller, so we don't
+ * have to call rcu_read_lock/unlock() in this function.
+ */
+static struct task_struct *find_early_kill_thread(struct task_struct *tsk)
+{
+	struct task_struct *t;
+
+	for_each_thread(tsk, t) {
+		if (t->flags & PF_MCE_PROCESS) {
+			if (t->flags & PF_MCE_EARLY)
+				return t;
+		} else {
+			if (sysctl_memory_failure_early_kill)
+				return t;
+		}
+	}
+	return NULL;
+}
+
+/*
+ * Determine whether a given process is "early kill" process which expects
+ * to be signaled when some page under the process is hwpoisoned.
+ * Return task_struct of the dedicated thread (main thread unless explicitly
+ * specified) if the process is "early kill," and otherwise returns NULL.
+ *
+ * Note that the above is true for Action Optional case, but not for Action
+ * Required case where SIGBUS should sent only to the current thread.
+ */
+static struct task_struct *task_early_kill(struct task_struct *tsk,
+					   int force_early)
+{
+	if (!tsk->mm)
+		return NULL;
+	if (force_early) {
+		/*
+		 * Comparing ->mm here because current task might represent
+		 * a subthread, while tsk always points to the main thread.
+		 */
+		if (tsk->mm == current->mm)
+			return current;
+		else
+			return NULL;
+	}
+	return find_early_kill_thread(tsk);
+}
+
+/*
+ * Collect processes when the error hit an anonymous page.
+ */
+static void collect_procs_anon(struct page *page, struct list_head *to_kill,
+				int force_early)
+{
+	struct vm_area_struct *vma;
+	struct task_struct *tsk;
+	struct anon_vma *av;
+	pgoff_t pgoff;
+
+	av = page_lock_anon_vma_read(page);
+	if (av == NULL)	/* Not actually mapped anymore */
+		return;
+
+	pgoff = page_to_pgoff(page);
+	read_lock(&tasklist_lock);
+	for_each_process (tsk) {
+		struct anon_vma_chain *vmac;
+		struct task_struct *t = task_early_kill(tsk, force_early);
+
+		if (!t)
+			continue;
+		anon_vma_interval_tree_foreach(vmac, &av->rb_root,
+					       pgoff, pgoff) {
+			vma = vmac->vma;
+			if (!page_mapped_in_vma(page, vma))
+				continue;
+			if (vma->vm_mm == t->mm)
+				add_to_kill(t, page, vma, to_kill);
+		}
+	}
+	read_unlock(&tasklist_lock);
+	page_unlock_anon_vma_read(av);
+}
+
+/*
+ * Collect processes when the error hit a file mapped page.
+ */
+static void collect_procs_file(struct page *page, struct list_head *to_kill,
+				int force_early)
+{
+	struct vm_area_struct *vma;
+	struct task_struct *tsk;
+	struct address_space *mapping = page->mapping;
+	pgoff_t pgoff;
+
+	i_mmap_lock_read(mapping);
+	read_lock(&tasklist_lock);
+	pgoff = page_to_pgoff(page);
+	for_each_process(tsk) {
+		struct task_struct *t = task_early_kill(tsk, force_early);
+
+		if (!t)
+			continue;
+		vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff,
+				      pgoff) {
+			/*
+			 * Send early kill signal to tasks where a vma covers
+			 * the page but the corrupted page is not necessarily
+			 * mapped it in its pte.
+			 * Assume applications who requested early kill want
+			 * to be informed of all such data corruptions.
+			 */
+			if (vma->vm_mm == t->mm)
+				add_to_kill(t, page, vma, to_kill);
+		}
+	}
+	read_unlock(&tasklist_lock);
+	i_mmap_unlock_read(mapping);
+}
+
+/*
+ * Collect the processes who have the corrupted page mapped to kill.
+ */
+static void collect_procs(struct page *page, struct list_head *tokill,
+				int force_early)
+{
+	if (!page->mapping)
+		return;
+
+	if (PageAnon(page))
+		collect_procs_anon(page, tokill, force_early);
+	else
+		collect_procs_file(page, tokill, force_early);
+}
+
+static const char *action_name[] = {
+	[MF_IGNORED] = "Ignored",
+	[MF_FAILED] = "Failed",
+	[MF_DELAYED] = "Delayed",
+	[MF_RECOVERED] = "Recovered",
+};
+
+static const char * const action_page_types[] = {
+	[MF_MSG_KERNEL]			= "reserved kernel page",
+	[MF_MSG_KERNEL_HIGH_ORDER]	= "high-order kernel page",
+	[MF_MSG_SLAB]			= "kernel slab page",
+	[MF_MSG_DIFFERENT_COMPOUND]	= "different compound page after locking",
+	[MF_MSG_POISONED_HUGE]		= "huge page already hardware poisoned",
+	[MF_MSG_HUGE]			= "huge page",
+	[MF_MSG_FREE_HUGE]		= "free huge page",
+	[MF_MSG_NON_PMD_HUGE]		= "non-pmd-sized huge page",
+	[MF_MSG_UNMAP_FAILED]		= "unmapping failed page",
+	[MF_MSG_DIRTY_SWAPCACHE]	= "dirty swapcache page",
+	[MF_MSG_CLEAN_SWAPCACHE]	= "clean swapcache page",
+	[MF_MSG_DIRTY_MLOCKED_LRU]	= "dirty mlocked LRU page",
+	[MF_MSG_CLEAN_MLOCKED_LRU]	= "clean mlocked LRU page",
+	[MF_MSG_DIRTY_UNEVICTABLE_LRU]	= "dirty unevictable LRU page",
+	[MF_MSG_CLEAN_UNEVICTABLE_LRU]	= "clean unevictable LRU page",
+	[MF_MSG_DIRTY_LRU]		= "dirty LRU page",
+	[MF_MSG_CLEAN_LRU]		= "clean LRU page",
+	[MF_MSG_TRUNCATED_LRU]		= "already truncated LRU page",
+	[MF_MSG_BUDDY]			= "free buddy page",
+	[MF_MSG_BUDDY_2ND]		= "free buddy page (2nd try)",
+	[MF_MSG_DAX]			= "dax page",
+	[MF_MSG_UNSPLIT_THP]		= "unsplit thp",
+	[MF_MSG_UNKNOWN]		= "unknown page",
+};
+
+/*
+ * XXX: It is possible that a page is isolated from LRU cache,
+ * and then kept in swap cache or failed to remove from page cache.
+ * The page count will stop it from being freed by unpoison.
+ * Stress tests should be aware of this memory leak problem.
+ */
+static int delete_from_lru_cache(struct page *p)
+{
+	if (!isolate_lru_page(p)) {
+		/*
+		 * Clear sensible page flags, so that the buddy system won't
+		 * complain when the page is unpoison-and-freed.
+		 */
+		ClearPageActive(p);
+		ClearPageUnevictable(p);
+
+		/*
+		 * Poisoned page might never drop its ref count to 0 so we have
+		 * to uncharge it manually from its memcg.
+		 */
+		mem_cgroup_uncharge(p);
+
+		/*
+		 * drop the page count elevated by isolate_lru_page()
+		 */
+		put_page(p);
+		return 0;
+	}
+	return -EIO;
+}
+
+static int truncate_error_page(struct page *p, unsigned long pfn,
+				struct address_space *mapping)
+{
+	int ret = MF_FAILED;
+
+	if (mapping->a_ops->error_remove_page) {
+		int err = mapping->a_ops->error_remove_page(mapping, p);
+
+		if (err != 0) {
+			pr_info("Memory failure: %#lx: Failed to punch page: %d\n",
+				pfn, err);
+		} else if (page_has_private(p) &&
+			   !try_to_release_page(p, GFP_NOIO)) {
+			pr_info("Memory failure: %#lx: failed to release buffers\n",
+				pfn);
+		} else {
+			ret = MF_RECOVERED;
+		}
+	} else {
+		/*
+		 * If the file system doesn't support it just invalidate
+		 * This fails on dirty or anything with private pages
+		 */
+		if (invalidate_inode_page(p))
+			ret = MF_RECOVERED;
+		else
+			pr_info("Memory failure: %#lx: Failed to invalidate\n",
+				pfn);
+	}
+
+	return ret;
+}
+
+/*
+ * Error hit kernel page.
+ * Do nothing, try to be lucky and not touch this instead. For a few cases we
+ * could be more sophisticated.
+ */
+static int me_kernel(struct page *p, unsigned long pfn)
+{
+	return MF_IGNORED;
+}
+
+/*
+ * Page in unknown state. Do nothing.
+ */
+static int me_unknown(struct page *p, unsigned long pfn)
+{
+	pr_err("Memory failure: %#lx: Unknown page state\n", pfn);
+	return MF_FAILED;
+}
+
+/*
+ * Clean (or cleaned) page cache page.
+ */
+static int me_pagecache_clean(struct page *p, unsigned long pfn)
+{
+	struct address_space *mapping;
+
+	delete_from_lru_cache(p);
+
+	/*
+	 * For anonymous pages we're done the only reference left
+	 * should be the one m_f() holds.
+	 */
+	if (PageAnon(p))
+		return MF_RECOVERED;
+
+	/*
+	 * Now truncate the page in the page cache. This is really
+	 * more like a "temporary hole punch"
+	 * Don't do this for block devices when someone else
+	 * has a reference, because it could be file system metadata
+	 * and that's not safe to truncate.
+	 */
+	mapping = page_mapping(p);
+	if (!mapping) {
+		/*
+		 * Page has been teared down in the meanwhile
+		 */
+		return MF_FAILED;
+	}
+
+	/*
+	 * Truncation is a bit tricky. Enable it per file system for now.
+	 *
+	 * Open: to take i_mutex or not for this? Right now we don't.
+	 */
+	return truncate_error_page(p, pfn, mapping);
+}
+
+/*
+ * Dirty pagecache page
+ * Issues: when the error hit a hole page the error is not properly
+ * propagated.
+ */
+static int me_pagecache_dirty(struct page *p, unsigned long pfn)
+{
+	struct address_space *mapping = page_mapping(p);
+
+	SetPageError(p);
+	/* TBD: print more information about the file. */
+	if (mapping) {
+		/*
+		 * IO error will be reported by write(), fsync(), etc.
+		 * who check the mapping.
+		 * This way the application knows that something went
+		 * wrong with its dirty file data.
+		 *
+		 * There's one open issue:
+		 *
+		 * The EIO will be only reported on the next IO
+		 * operation and then cleared through the IO map.
+		 * Normally Linux has two mechanisms to pass IO error
+		 * first through the AS_EIO flag in the address space
+		 * and then through the PageError flag in the page.
+		 * Since we drop pages on memory failure handling the
+		 * only mechanism open to use is through AS_AIO.
+		 *
+		 * This has the disadvantage that it gets cleared on
+		 * the first operation that returns an error, while
+		 * the PageError bit is more sticky and only cleared
+		 * when the page is reread or dropped.  If an
+		 * application assumes it will always get error on
+		 * fsync, but does other operations on the fd before
+		 * and the page is dropped between then the error
+		 * will not be properly reported.
+		 *
+		 * This can already happen even without hwpoisoned
+		 * pages: first on metadata IO errors (which only
+		 * report through AS_EIO) or when the page is dropped
+		 * at the wrong time.
+		 *
+		 * So right now we assume that the application DTRT on
+		 * the first EIO, but we're not worse than other parts
+		 * of the kernel.
+		 */
+		mapping_set_error(mapping, -EIO);
+	}
+
+	return me_pagecache_clean(p, pfn);
+}
+
+/*
+ * Clean and dirty swap cache.
+ *
+ * Dirty swap cache page is tricky to handle. The page could live both in page
+ * cache and swap cache(ie. page is freshly swapped in). So it could be
+ * referenced concurrently by 2 types of PTEs:
+ * normal PTEs and swap PTEs. We try to handle them consistently by calling
+ * try_to_unmap(TTU_IGNORE_HWPOISON) to convert the normal PTEs to swap PTEs,
+ * and then
+ *      - clear dirty bit to prevent IO
+ *      - remove from LRU
+ *      - but keep in the swap cache, so that when we return to it on
+ *        a later page fault, we know the application is accessing
+ *        corrupted data and shall be killed (we installed simple
+ *        interception code in do_swap_page to catch it).
+ *
+ * Clean swap cache pages can be directly isolated. A later page fault will
+ * bring in the known good data from disk.
+ */
+static int me_swapcache_dirty(struct page *p, unsigned long pfn)
+{
+	ClearPageDirty(p);
+	/* Trigger EIO in shmem: */
+	ClearPageUptodate(p);
+
+	if (!delete_from_lru_cache(p))
+		return MF_DELAYED;
+	else
+		return MF_FAILED;
+}
+
+static int me_swapcache_clean(struct page *p, unsigned long pfn)
+{
+	delete_from_swap_cache(p);
+
+	if (!delete_from_lru_cache(p))
+		return MF_RECOVERED;
+	else
+		return MF_FAILED;
+}
+
+/*
+ * Huge pages. Needs work.
+ * Issues:
+ * - Error on hugepage is contained in hugepage unit (not in raw page unit.)
+ *   To narrow down kill region to one page, we need to break up pmd.
+ */
+static int me_huge_page(struct page *p, unsigned long pfn)
+{
+	int res = 0;
+	struct page *hpage = compound_head(p);
+	struct address_space *mapping;
+
+	if (!PageHuge(hpage))
+		return MF_DELAYED;
+
+	mapping = page_mapping(hpage);
+	if (mapping) {
+		res = truncate_error_page(hpage, pfn, mapping);
+	} else {
+		unlock_page(hpage);
+		/*
+		 * migration entry prevents later access on error anonymous
+		 * hugepage, so we can free and dissolve it into buddy to
+		 * save healthy subpages.
+		 */
+		if (PageAnon(hpage))
+			put_page(hpage);
+		dissolve_free_huge_page(p);
+		res = MF_RECOVERED;
+		lock_page(hpage);
+	}
+
+	return res;
+}
+
+/*
+ * Various page states we can handle.
+ *
+ * A page state is defined by its current page->flags bits.
+ * The table matches them in order and calls the right handler.
+ *
+ * This is quite tricky because we can access page at any time
+ * in its live cycle, so all accesses have to be extremely careful.
+ *
+ * This is not complete. More states could be added.
+ * For any missing state don't attempt recovery.
+ */
+
+#define dirty		(1UL << PG_dirty)
+#define sc		((1UL << PG_swapcache) | (1UL << PG_swapbacked))
+#define unevict		(1UL << PG_unevictable)
+#define mlock		(1UL << PG_mlocked)
+#define lru		(1UL << PG_lru)
+#define head		(1UL << PG_head)
+#define slab		(1UL << PG_slab)
+#define reserved	(1UL << PG_reserved)
+
+static struct page_state {
+	unsigned long mask;
+	unsigned long res;
+	enum mf_action_page_type type;
+	int (*action)(struct page *p, unsigned long pfn);
+} error_states[] = {
+	{ reserved,	reserved,	MF_MSG_KERNEL,	me_kernel },
+	/*
+	 * free pages are specially detected outside this table:
+	 * PG_buddy pages only make a small fraction of all free pages.
+	 */
+
+	/*
+	 * Could in theory check if slab page is free or if we can drop
+	 * currently unused objects without touching them. But just
+	 * treat it as standard kernel for now.
+	 */
+	{ slab,		slab,		MF_MSG_SLAB,	me_kernel },
+
+	{ head,		head,		MF_MSG_HUGE,		me_huge_page },
+
+	{ sc|dirty,	sc|dirty,	MF_MSG_DIRTY_SWAPCACHE,	me_swapcache_dirty },
+	{ sc|dirty,	sc,		MF_MSG_CLEAN_SWAPCACHE,	me_swapcache_clean },
+
+	{ mlock|dirty,	mlock|dirty,	MF_MSG_DIRTY_MLOCKED_LRU,	me_pagecache_dirty },
+	{ mlock|dirty,	mlock,		MF_MSG_CLEAN_MLOCKED_LRU,	me_pagecache_clean },
+
+	{ unevict|dirty, unevict|dirty,	MF_MSG_DIRTY_UNEVICTABLE_LRU,	me_pagecache_dirty },
+	{ unevict|dirty, unevict,	MF_MSG_CLEAN_UNEVICTABLE_LRU,	me_pagecache_clean },
+
+	{ lru|dirty,	lru|dirty,	MF_MSG_DIRTY_LRU,	me_pagecache_dirty },
+	{ lru|dirty,	lru,		MF_MSG_CLEAN_LRU,	me_pagecache_clean },
+
+	/*
+	 * Catchall entry: must be at end.
+	 */
+	{ 0,		0,		MF_MSG_UNKNOWN,	me_unknown },
+};
+
+#undef dirty
+#undef sc
+#undef unevict
+#undef mlock
+#undef lru
+#undef head
+#undef slab
+#undef reserved
+
+/*
+ * "Dirty/Clean" indication is not 100% accurate due to the possibility of
+ * setting PG_dirty outside page lock. See also comment above set_page_dirty().
+ */
+static void action_result(unsigned long pfn, enum mf_action_page_type type,
+			  enum mf_result result)
+{
+	trace_memory_failure_event(pfn, type, result);
+
+	pr_err("Memory failure: %#lx: recovery action for %s: %s\n",
+		pfn, action_page_types[type], action_name[result]);
+}
+
+static int page_action(struct page_state *ps, struct page *p,
+			unsigned long pfn)
+{
+	int result;
+	int count;
+
+	result = ps->action(p, pfn);
+
+	count = page_count(p) - 1;
+	if (ps->action == me_swapcache_dirty && result == MF_DELAYED)
+		count--;
+	if (count > 0) {
+		pr_err("Memory failure: %#lx: %s still referenced by %d users\n",
+		       pfn, action_page_types[ps->type], count);
+		result = MF_FAILED;
+	}
+	action_result(pfn, ps->type, result);
+
+	/* Could do more checks here if page looks ok */
+	/*
+	 * Could adjust zone counters here to correct for the missing page.
+	 */
+
+	return (result == MF_RECOVERED || result == MF_DELAYED) ? 0 : -EBUSY;
+}
+
+/**
+ * get_hwpoison_page() - Get refcount for memory error handling:
+ * @page:	raw error page (hit by memory error)
+ *
+ * Return: return 0 if failed to grab the refcount, otherwise true (some
+ * non-zero value.)
+ */
+static int get_hwpoison_page(struct page *page)
+{
+	struct page *head = compound_head(page);
+
+	if (!PageHuge(head) && PageTransHuge(head)) {
+		/*
+		 * Non anonymous thp exists only in allocation/free time. We
+		 * can't handle such a case correctly, so let's give it up.
+		 * This should be better than triggering BUG_ON when kernel
+		 * tries to touch the "partially handled" page.
+		 */
+		if (!PageAnon(head)) {
+			pr_err("Memory failure: %#lx: non anonymous thp\n",
+				page_to_pfn(page));
+			return 0;
+		}
+	}
+
+	if (get_page_unless_zero(head)) {
+		if (head == compound_head(page))
+			return 1;
+
+		pr_info("Memory failure: %#lx cannot catch tail\n",
+			page_to_pfn(page));
+		put_page(head);
+	}
+
+	return 0;
+}
+
+/*
+ * Do all that is necessary to remove user space mappings. Unmap
+ * the pages and send SIGBUS to the processes if the data was dirty.
+ */
+static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
+				  int flags, struct page **hpagep)
+{
+	enum ttu_flags ttu = TTU_IGNORE_MLOCK;
+	struct address_space *mapping;
+	LIST_HEAD(tokill);
+	bool unmap_success = true;
+	int kill = 1, forcekill;
+	struct page *hpage = *hpagep;
+	bool mlocked = PageMlocked(hpage);
+
+	/*
+	 * Here we are interested only in user-mapped pages, so skip any
+	 * other types of pages.
+	 */
+	if (PageReserved(p) || PageSlab(p))
+		return true;
+	if (!(PageLRU(hpage) || PageHuge(p)))
+		return true;
+
+	/*
+	 * This check implies we don't kill processes if their pages
+	 * are in the swap cache early. Those are always late kills.
+	 */
+	if (!page_mapped(p))
+		return true;
+
+	if (PageKsm(p)) {
+		pr_err("Memory failure: %#lx: can't handle KSM pages.\n", pfn);
+		return false;
+	}
+
+	if (PageSwapCache(p)) {
+		pr_err("Memory failure: %#lx: keeping poisoned page in swap cache\n",
+			pfn);
+		ttu |= TTU_IGNORE_HWPOISON;
+	}
+
+	/*
+	 * Propagate the dirty bit from PTEs to struct page first, because we
+	 * need this to decide if we should kill or just drop the page.
+	 * XXX: the dirty test could be racy: set_page_dirty() may not always
+	 * be called inside page lock (it's recommended but not enforced).
+	 */
+	mapping = page_mapping(hpage);
+	if (!(flags & MF_MUST_KILL) && !PageDirty(hpage) && mapping &&
+	    mapping_can_writeback(mapping)) {
+		if (page_mkclean(hpage)) {
+			SetPageDirty(hpage);
+		} else {
+			kill = 0;
+			ttu |= TTU_IGNORE_HWPOISON;
+			pr_info("Memory failure: %#lx: corrupted page was clean: dropped without side effects\n",
+				pfn);
+		}
+	}
+
+	/*
+	 * First collect all the processes that have the page
+	 * mapped in dirty form.  This has to be done before try_to_unmap,
+	 * because ttu takes the rmap data structures down.
+	 *
+	 * Error handling: We ignore errors here because
+	 * there's nothing that can be done.
+	 */
+	if (kill)
+		collect_procs(hpage, &tokill, flags & MF_ACTION_REQUIRED);
+
+	if (!PageHuge(hpage)) {
+		unmap_success = try_to_unmap(hpage, ttu);
+	} else {
+		if (!PageAnon(hpage)) {
+			/*
+			 * For hugetlb pages in shared mappings, try_to_unmap
+			 * could potentially call huge_pmd_unshare.  Because of
+			 * this, take semaphore in write mode here and set
+			 * TTU_RMAP_LOCKED to indicate we have taken the lock
+			 * at this higer level.
+			 */
+			mapping = hugetlb_page_mapping_lock_write(hpage);
+			if (mapping) {
+				unmap_success = try_to_unmap(hpage,
+						     ttu|TTU_RMAP_LOCKED);
+				i_mmap_unlock_write(mapping);
+			} else {
+				pr_info("Memory failure: %#lx: could not lock mapping for mapped huge page\n", pfn);
+				unmap_success = false;
+			}
+		} else {
+			unmap_success = try_to_unmap(p, ttu);
+		}
+	}
+	if (!unmap_success)
+		pr_err("Memory failure: %#lx: failed to unmap page (mapcount=%d)\n",
+		       pfn, page_mapcount(p));
+
+	/*
+	 * try_to_unmap() might put mlocked page in lru cache, so call
+	 * shake_page() again to ensure that it's flushed.
+	 */
+	if (mlocked)
+		shake_page(hpage, 0);
+
+	/*
+	 * Now that the dirty bit has been propagated to the
+	 * struct page and all unmaps done we can decide if
+	 * killing is needed or not.  Only kill when the page
+	 * was dirty or the process is not restartable,
+	 * otherwise the tokill list is merely
+	 * freed.  When there was a problem unmapping earlier
+	 * use a more force-full uncatchable kill to prevent
+	 * any accesses to the poisoned memory.
+	 */
+	forcekill = PageDirty(hpage) || (flags & MF_MUST_KILL);
+	kill_procs(&tokill, forcekill, !unmap_success, pfn, flags);
+
+	return unmap_success;
+}
+
+static int identify_page_state(unsigned long pfn, struct page *p,
+				unsigned long page_flags)
+{
+	struct page_state *ps;
+
+	/*
+	 * The first check uses the current page flags which may not have any
+	 * relevant information. The second check with the saved page flags is
+	 * carried out only if the first check can't determine the page status.
+	 */
+	for (ps = error_states;; ps++)
+		if ((p->flags & ps->mask) == ps->res)
+			break;
+
+	page_flags |= (p->flags & (1UL << PG_dirty));
+
+	if (!ps->mask)
+		for (ps = error_states;; ps++)
+			if ((page_flags & ps->mask) == ps->res)
+				break;
+	return page_action(ps, p, pfn);
+}
+
+static int try_to_split_thp_page(struct page *page, const char *msg)
+{
+	lock_page(page);
+	if (!PageAnon(page) || unlikely(split_huge_page(page))) {
+		unsigned long pfn = page_to_pfn(page);
+
+		unlock_page(page);
+		if (!PageAnon(page))
+			pr_info("%s: %#lx: non anonymous thp\n", msg, pfn);
+		else
+			pr_info("%s: %#lx: thp split failed\n", msg, pfn);
+		put_page(page);
+		return -EBUSY;
+	}
+	unlock_page(page);
+
+	return 0;
+}
+
+static int memory_failure_hugetlb(unsigned long pfn, int flags)
+{
+	struct page *p = pfn_to_page(pfn);
+	struct page *head = compound_head(p);
+	int res;
+	unsigned long page_flags;
+
+	if (TestSetPageHWPoison(head)) {
+		pr_err("Memory failure: %#lx: already hardware poisoned\n",
+		       pfn);
+		return 0;
+	}
+
+	num_poisoned_pages_inc();
+
+	if (!(flags & MF_COUNT_INCREASED) && !get_hwpoison_page(p)) {
+		/*
+		 * Check "filter hit" and "race with other subpage."
+		 */
+		lock_page(head);
+		if (PageHWPoison(head)) {
+			if ((hwpoison_filter(p) && TestClearPageHWPoison(p))
+			    || (p != head && TestSetPageHWPoison(head))) {
+				num_poisoned_pages_dec();
+				unlock_page(head);
+				return 0;
+			}
+		}
+		unlock_page(head);
+		dissolve_free_huge_page(p);
+		action_result(pfn, MF_MSG_FREE_HUGE, MF_DELAYED);
+		return 0;
+	}
+
+	lock_page(head);
+	page_flags = head->flags;
+
+	if (!PageHWPoison(head)) {
+		pr_err("Memory failure: %#lx: just unpoisoned\n", pfn);
+		num_poisoned_pages_dec();
+		unlock_page(head);
+		put_page(head);
+		return 0;
+	}
+
+	/*
+	 * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so
+	 * simply disable it. In order to make it work properly, we need
+	 * make sure that:
+	 *  - conversion of a pud that maps an error hugetlb into hwpoison
+	 *    entry properly works, and
+	 *  - other mm code walking over page table is aware of pud-aligned
+	 *    hwpoison entries.
+	 */
+	if (huge_page_size(page_hstate(head)) > PMD_SIZE) {
+		action_result(pfn, MF_MSG_NON_PMD_HUGE, MF_IGNORED);
+		res = -EBUSY;
+		goto out;
+	}
+
+	if (!hwpoison_user_mappings(p, pfn, flags, &head)) {
+		action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED);
+		res = -EBUSY;
+		goto out;
+	}
+
+	res = identify_page_state(pfn, p, page_flags);
+out:
+	unlock_page(head);
+	return res;
+}
+
+static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
+		struct dev_pagemap *pgmap)
+{
+	struct page *page = pfn_to_page(pfn);
+	const bool unmap_success = true;
+	unsigned long size = 0;
+	struct to_kill *tk;
+	LIST_HEAD(tokill);
+	int rc = -EBUSY;
+	loff_t start;
+	dax_entry_t cookie;
+
+	if (flags & MF_COUNT_INCREASED)
+		/*
+		 * Drop the extra refcount in case we come from madvise().
+		 */
+		put_page(page);
+
+	/* device metadata space is not recoverable */
+	if (!pgmap_pfn_valid(pgmap, pfn)) {
+		rc = -ENXIO;
+		goto out;
+	}
+
+	/*
+	 * Prevent the inode from being freed while we are interrogating
+	 * the address_space, typically this would be handled by
+	 * lock_page(), but dax pages do not use the page lock. This
+	 * also prevents changes to the mapping of this pfn until
+	 * poison signaling is complete.
+	 */
+	cookie = dax_lock_page(page);
+	if (!cookie)
+		goto out;
+
+	if (hwpoison_filter(page)) {
+		rc = 0;
+		goto unlock;
+	}
+
+	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
+		/*
+		 * TODO: Handle HMM pages which may need coordination
+		 * with device-side memory.
+		 */
+		goto unlock;
+	}
+
+	/*
+	 * Use this flag as an indication that the dax page has been
+	 * remapped UC to prevent speculative consumption of poison.
+	 */
+	SetPageHWPoison(page);
+
+	/*
+	 * Unlike System-RAM there is no possibility to swap in a
+	 * different physical page at a given virtual address, so all
+	 * userspace consumption of ZONE_DEVICE memory necessitates
+	 * SIGBUS (i.e. MF_MUST_KILL)
+	 */
+	flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
+	collect_procs(page, &tokill, flags & MF_ACTION_REQUIRED);
+
+	list_for_each_entry(tk, &tokill, nd)
+		if (tk->size_shift)
+			size = max(size, 1UL << tk->size_shift);
+	if (size) {
+		/*
+		 * Unmap the largest mapping to avoid breaking up
+		 * device-dax mappings which are constant size. The
+		 * actual size of the mapping being torn down is
+		 * communicated in siginfo, see kill_proc()
+		 */
+		start = (page->index << PAGE_SHIFT) & ~(size - 1);
+		unmap_mapping_range(page->mapping, start, size, 0);
+	}
+	kill_procs(&tokill, flags & MF_MUST_KILL, !unmap_success, pfn, flags);
+	rc = 0;
+unlock:
+	dax_unlock_page(page, cookie);
+out:
+	/* drop pgmap ref acquired in caller */
+	put_dev_pagemap(pgmap);
+	action_result(pfn, MF_MSG_DAX, rc ? MF_FAILED : MF_RECOVERED);
+	return rc;
+}
+
+/**
+ * memory_failure - Handle memory failure of a page.
+ * @pfn: Page Number of the corrupted page
+ * @flags: fine tune action taken
+ *
+ * This function is called by the low level machine check code
+ * of an architecture when it detects hardware memory corruption
+ * of a page. It tries its best to recover, which includes
+ * dropping pages, killing processes etc.
+ *
+ * The function is primarily of use for corruptions that
+ * happen outside the current execution context (e.g. when
+ * detected by a background scrubber)
+ *
+ * Must run in process context (e.g. a work queue) with interrupts
+ * enabled and no spinlocks hold.
+ */
+int memory_failure(unsigned long pfn, int flags)
+{
+	struct page *p;
+	struct page *hpage;
+	struct page *orig_head;
+	struct dev_pagemap *pgmap;
+	int res;
+	unsigned long page_flags;
+
+	if (!sysctl_memory_failure_recovery)
+		panic("Memory failure on page %lx", pfn);
+
+	p = pfn_to_online_page(pfn);
+	if (!p) {
+		if (pfn_valid(pfn)) {
+			pgmap = get_dev_pagemap(pfn, NULL);
+			if (pgmap)
+				return memory_failure_dev_pagemap(pfn, flags,
+								  pgmap);
+		}
+		pr_err("Memory failure: %#lx: memory outside kernel control\n",
+			pfn);
+		return -ENXIO;
+	}
+
+	if (PageHuge(p))
+		return memory_failure_hugetlb(pfn, flags);
+	if (TestSetPageHWPoison(p)) {
+		pr_err("Memory failure: %#lx: already hardware poisoned\n",
+			pfn);
+		return 0;
+	}
+
+	orig_head = hpage = compound_head(p);
+	num_poisoned_pages_inc();
+
+	/*
+	 * We need/can do nothing about count=0 pages.
+	 * 1) it's a free page, and therefore in safe hand:
+	 *    prep_new_page() will be the gate keeper.
+	 * 2) it's part of a non-compound high order page.
+	 *    Implies some kernel user: cannot stop them from
+	 *    R/W the page; let's pray that the page has been
+	 *    used and will be freed some time later.
+	 * In fact it's dangerous to directly bump up page count from 0,
+	 * that may make page_ref_freeze()/page_ref_unfreeze() mismatch.
+	 */
+	if (!(flags & MF_COUNT_INCREASED) && !get_hwpoison_page(p)) {
+		if (is_free_buddy_page(p)) {
+			action_result(pfn, MF_MSG_BUDDY, MF_DELAYED);
+			return 0;
+		} else {
+			action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED);
+			return -EBUSY;
+		}
+	}
+
+	if (PageTransHuge(hpage)) {
+		if (try_to_split_thp_page(p, "Memory Failure") < 0) {
+			action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED);
+			return -EBUSY;
+		}
+		VM_BUG_ON_PAGE(!page_count(p), p);
+	}
+
+	/*
+	 * We ignore non-LRU pages for good reasons.
+	 * - PG_locked is only well defined for LRU pages and a few others
+	 * - to avoid races with __SetPageLocked()
+	 * - to avoid races with __SetPageSlab*() (and more non-atomic ops)
+	 * The check (unnecessarily) ignores LRU pages being isolated and
+	 * walked by the page reclaim code, however that's not a big loss.
+	 */
+	shake_page(p, 0);
+	/* shake_page could have turned it free. */
+	if (!PageLRU(p) && is_free_buddy_page(p)) {
+		if (flags & MF_COUNT_INCREASED)
+			action_result(pfn, MF_MSG_BUDDY, MF_DELAYED);
+		else
+			action_result(pfn, MF_MSG_BUDDY_2ND, MF_DELAYED);
+		return 0;
+	}
+
+	lock_page(p);
+
+	/*
+	 * The page could have changed compound pages during the locking.
+	 * If this happens just bail out.
+	 */
+	if (PageCompound(p) && compound_head(p) != orig_head) {
+		action_result(pfn, MF_MSG_DIFFERENT_COMPOUND, MF_IGNORED);
+		res = -EBUSY;
+		goto out;
+	}
+
+	/*
+	 * We use page flags to determine what action should be taken, but
+	 * the flags can be modified by the error containment action.  One
+	 * example is an mlocked page, where PG_mlocked is cleared by
+	 * page_remove_rmap() in try_to_unmap_one(). So to determine page status
+	 * correctly, we save a copy of the page flags at this time.
+	 */
+	page_flags = p->flags;
+
+	/*
+	 * unpoison always clear PG_hwpoison inside page lock
+	 */
+	if (!PageHWPoison(p)) {
+		pr_err("Memory failure: %#lx: just unpoisoned\n", pfn);
+		num_poisoned_pages_dec();
+		unlock_page(p);
+		put_page(p);
+		return 0;
+	}
+	if (hwpoison_filter(p)) {
+		if (TestClearPageHWPoison(p))
+			num_poisoned_pages_dec();
+		unlock_page(p);
+		put_page(p);
+		return 0;
+	}
+
+	/*
+	 * __munlock_pagevec may clear a writeback page's LRU flag without
+	 * page_lock. We need wait writeback completion for this page or it
+	 * may trigger vfs BUG while evict inode.
+	 */
+	if (!PageTransTail(p) && !PageLRU(p) && !PageWriteback(p))
+		goto identify_page_state;
+
+	/*
+	 * It's very difficult to mess with pages currently under IO
+	 * and in many cases impossible, so we just avoid it here.
+	 */
+	wait_on_page_writeback(p);
+
+	/*
+	 * Now take care of user space mappings.
+	 * Abort on fail: __delete_from_page_cache() assumes unmapped page.
+	 */
+	if (!hwpoison_user_mappings(p, pfn, flags, &p)) {
+		action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED);
+		res = -EBUSY;
+		goto out;
+	}
+
+	/*
+	 * Torn down by someone else?
+	 */
+	if (PageLRU(p) && !PageSwapCache(p) && p->mapping == NULL) {
+		action_result(pfn, MF_MSG_TRUNCATED_LRU, MF_IGNORED);
+		res = -EBUSY;
+		goto out;
+	}
+
+identify_page_state:
+	res = identify_page_state(pfn, p, page_flags);
+out:
+	unlock_page(p);
+	return res;
+}
+EXPORT_SYMBOL_GPL(memory_failure);
+
+#define MEMORY_FAILURE_FIFO_ORDER	4
+#define MEMORY_FAILURE_FIFO_SIZE	(1 << MEMORY_FAILURE_FIFO_ORDER)
+
+struct memory_failure_entry {
+	unsigned long pfn;
+	int flags;
+};
+
+struct memory_failure_cpu {
+	DECLARE_KFIFO(fifo, struct memory_failure_entry,
+		      MEMORY_FAILURE_FIFO_SIZE);
+	spinlock_t lock;
+	struct work_struct work;
+};
+
+static DEFINE_PER_CPU(struct memory_failure_cpu, memory_failure_cpu);
+
+/**
+ * memory_failure_queue - Schedule handling memory failure of a page.
+ * @pfn: Page Number of the corrupted page
+ * @flags: Flags for memory failure handling
+ *
+ * This function is called by the low level hardware error handler
+ * when it detects hardware memory corruption of a page. It schedules
+ * the recovering of error page, including dropping pages, killing
+ * processes etc.
+ *
+ * The function is primarily of use for corruptions that
+ * happen outside the current execution context (e.g. when
+ * detected by a background scrubber)
+ *
+ * Can run in IRQ context.
+ */
+void memory_failure_queue(unsigned long pfn, int flags)
+{
+	struct memory_failure_cpu *mf_cpu;
+	unsigned long proc_flags;
+	struct memory_failure_entry entry = {
+		.pfn =		pfn,
+		.flags =	flags,
+	};
+
+	mf_cpu = &get_cpu_var(memory_failure_cpu);
+	spin_lock_irqsave(&mf_cpu->lock, proc_flags);
+	if (kfifo_put(&mf_cpu->fifo, entry))
+		schedule_work_on(smp_processor_id(), &mf_cpu->work);
+	else
+		pr_err("Memory failure: buffer overflow when queuing memory failure at %#lx\n",
+		       pfn);
+	spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
+	put_cpu_var(memory_failure_cpu);
+}
+EXPORT_SYMBOL_GPL(memory_failure_queue);
+
+static void memory_failure_work_func(struct work_struct *work)
+{
+	struct memory_failure_cpu *mf_cpu;
+	struct memory_failure_entry entry = { 0, };
+	unsigned long proc_flags;
+	int gotten;
+
+	mf_cpu = container_of(work, struct memory_failure_cpu, work);
+	for (;;) {
+		spin_lock_irqsave(&mf_cpu->lock, proc_flags);
+		gotten = kfifo_get(&mf_cpu->fifo, &entry);
+		spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
+		if (!gotten)
+			break;
+		if (entry.flags & MF_SOFT_OFFLINE)
+			soft_offline_page(entry.pfn, entry.flags);
+		else
+			memory_failure(entry.pfn, entry.flags);
+	}
+}
+
+/*
+ * Process memory_failure work queued on the specified CPU.
+ * Used to avoid return-to-userspace racing with the memory_failure workqueue.
+ */
+void memory_failure_queue_kick(int cpu)
+{
+	struct memory_failure_cpu *mf_cpu;
+
+	mf_cpu = &per_cpu(memory_failure_cpu, cpu);
+	cancel_work_sync(&mf_cpu->work);
+	memory_failure_work_func(&mf_cpu->work);
+}
+
+static int __init memory_failure_init(void)
+{
+	struct memory_failure_cpu *mf_cpu;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		mf_cpu = &per_cpu(memory_failure_cpu, cpu);
+		spin_lock_init(&mf_cpu->lock);
+		INIT_KFIFO(mf_cpu->fifo);
+		INIT_WORK(&mf_cpu->work, memory_failure_work_func);
+	}
+
+	return 0;
+}
+core_initcall(memory_failure_init);
+
+#define unpoison_pr_info(fmt, pfn, rs)			\
+({							\
+	if (__ratelimit(rs))				\
+		pr_info(fmt, pfn);			\
+})
+
+/**
+ * unpoison_memory - Unpoison a previously poisoned page
+ * @pfn: Page number of the to be unpoisoned page
+ *
+ * Software-unpoison a page that has been poisoned by
+ * memory_failure() earlier.
+ *
+ * This is only done on the software-level, so it only works
+ * for linux injected failures, not real hardware failures
+ *
+ * Returns 0 for success, otherwise -errno.
+ */
+int unpoison_memory(unsigned long pfn)
+{
+	struct page *page;
+	struct page *p;
+	int freeit = 0;
+	static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
+					DEFAULT_RATELIMIT_BURST);
+
+	if (!pfn_valid(pfn))
+		return -ENXIO;
+
+	p = pfn_to_page(pfn);
+	page = compound_head(p);
+
+	if (!PageHWPoison(p)) {
+		unpoison_pr_info("Unpoison: Page was already unpoisoned %#lx\n",
+				 pfn, &unpoison_rs);
+		return 0;
+	}
+
+	if (page_count(page) > 1) {
+		unpoison_pr_info("Unpoison: Someone grabs the hwpoison page %#lx\n",
+				 pfn, &unpoison_rs);
+		return 0;
+	}
+
+	if (page_mapped(page)) {
+		unpoison_pr_info("Unpoison: Someone maps the hwpoison page %#lx\n",
+				 pfn, &unpoison_rs);
+		return 0;
+	}
+
+	if (page_mapping(page)) {
+		unpoison_pr_info("Unpoison: the hwpoison page has non-NULL mapping %#lx\n",
+				 pfn, &unpoison_rs);
+		return 0;
+	}
+
+	/*
+	 * unpoison_memory() can encounter thp only when the thp is being
+	 * worked by memory_failure() and the page lock is not held yet.
+	 * In such case, we yield to memory_failure() and make unpoison fail.
+	 */
+	if (!PageHuge(page) && PageTransHuge(page)) {
+		unpoison_pr_info("Unpoison: Memory failure is now running on %#lx\n",
+				 pfn, &unpoison_rs);
+		return 0;
+	}
+
+	if (!get_hwpoison_page(p)) {
+		if (TestClearPageHWPoison(p))
+			num_poisoned_pages_dec();
+		unpoison_pr_info("Unpoison: Software-unpoisoned free page %#lx\n",
+				 pfn, &unpoison_rs);
+		return 0;
+	}
+
+	lock_page(page);
+	/*
+	 * This test is racy because PG_hwpoison is set outside of page lock.
+	 * That's acceptable because that won't trigger kernel panic. Instead,
+	 * the PG_hwpoison page will be caught and isolated on the entrance to
+	 * the free buddy page pool.
+	 */
+	if (TestClearPageHWPoison(page)) {
+		unpoison_pr_info("Unpoison: Software-unpoisoned page %#lx\n",
+				 pfn, &unpoison_rs);
+		num_poisoned_pages_dec();
+		freeit = 1;
+	}
+	unlock_page(page);
+
+	put_page(page);
+	if (freeit && !(pfn == my_zero_pfn(0) && page_count(p) == 1))
+		put_page(page);
+
+	return 0;
+}
+EXPORT_SYMBOL(unpoison_memory);
+
+/*
+ * Safely get reference count of an arbitrary page.
+ * Returns 0 for a free page, 1 for an in-use page, -EIO for a page-type we
+ * cannot handle and -EBUSY if we raced with an allocation.
+ * We only incremented refcount in case the page was already in-use and it is
+ * a known type we can handle.
+ */
+static int get_any_page(struct page *p, int flags)
+{
+	int ret = 0, pass = 0;
+	bool count_increased = false;
+
+	if (flags & MF_COUNT_INCREASED)
+		count_increased = true;
+
+try_again:
+	if (!count_increased && !get_hwpoison_page(p)) {
+		if (page_count(p)) {
+			/* We raced with an allocation, retry. */
+			if (pass++ < 3)
+				goto try_again;
+			ret = -EBUSY;
+		} else if (!PageHuge(p) && !is_free_buddy_page(p)) {
+			/* We raced with put_page, retry. */
+			if (pass++ < 3)
+				goto try_again;
+			ret = -EIO;
+		}
+	} else {
+		if (PageHuge(p) || PageLRU(p) || __PageMovable(p)) {
+			ret = 1;
+		} else {
+			/*
+			 * A page we cannot handle. Check whether we can turn
+			 * it into something we can handle.
+			 */
+			if (pass++ < 3) {
+				put_page(p);
+				shake_page(p, 1);
+				count_increased = false;
+				goto try_again;
+			}
+			put_page(p);
+			ret = -EIO;
+		}
+	}
+
+	return ret;
+}
+
+static bool isolate_page(struct page *page, struct list_head *pagelist)
+{
+	bool isolated = false;
+	bool lru = PageLRU(page);
+
+	if (PageHuge(page)) {
+		isolated = !isolate_hugetlb(page, pagelist);
+	} else {
+		if (lru)
+			isolated = !isolate_lru_page(page);
+		else
+			isolated = !isolate_movable_page(page, ISOLATE_UNEVICTABLE);
+
+		if (isolated)
+			list_add(&page->lru, pagelist);
+	}
+
+	if (isolated && lru)
+		inc_node_page_state(page, NR_ISOLATED_ANON +
+				    page_is_file_lru(page));
+
+	/*
+	 * If we succeed to isolate the page, we grabbed another refcount on
+	 * the page, so we can safely drop the one we got from get_any_pages().
+	 * If we failed to isolate the page, it means that we cannot go further
+	 * and we will return an error, so drop the reference we got from
+	 * get_any_pages() as well.
+	 */
+	put_page(page);
+	return isolated;
+}
+
+/*
+ * __soft_offline_page handles hugetlb-pages and non-hugetlb pages.
+ * If the page is a non-dirty unmapped page-cache page, it simply invalidates.
+ * If the page is mapped, it migrates the contents over.
+ */
+static int __soft_offline_page(struct page *page)
+{
+	int ret = 0;
+	unsigned long pfn = page_to_pfn(page);
+	struct page *hpage = compound_head(page);
+	char const *msg_page[] = {"page", "hugepage"};
+	bool huge = PageHuge(page);
+	LIST_HEAD(pagelist);
+	struct migration_target_control mtc = {
+		.nid = NUMA_NO_NODE,
+		.gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL,
+	};
+
+	/*
+	 * Check PageHWPoison again inside page lock because PageHWPoison
+	 * is set by memory_failure() outside page lock. Note that
+	 * memory_failure() also double-checks PageHWPoison inside page lock,
+	 * so there's no race between soft_offline_page() and memory_failure().
+	 */
+	lock_page(page);
+	if (!PageHuge(page))
+		wait_on_page_writeback(page);
+	if (PageHWPoison(page)) {
+		unlock_page(page);
+		put_page(page);
+		pr_info("soft offline: %#lx page already poisoned\n", pfn);
+		return 0;
+	}
+
+	if (!PageHuge(page))
+		/*
+		 * Try to invalidate first. This should work for
+		 * non dirty unmapped page cache pages.
+		 */
+		ret = invalidate_inode_page(page);
+	unlock_page(page);
+
+	/*
+	 * RED-PEN would be better to keep it isolated here, but we
+	 * would need to fix isolation locking first.
+	 */
+	if (ret) {
+		pr_info("soft_offline: %#lx: invalidated\n", pfn);
+		page_handle_poison(page, false, true);
+		return 0;
+	}
+
+	if (isolate_page(hpage, &pagelist)) {
+		ret = migrate_pages(&pagelist, alloc_migration_target, NULL,
+			(unsigned long)&mtc, MIGRATE_SYNC, MR_MEMORY_FAILURE);
+		if (!ret) {
+			bool release = !huge;
+
+			if (!page_handle_poison(page, huge, release))
+				ret = -EBUSY;
+		} else {
+			if (!list_empty(&pagelist))
+				putback_movable_pages(&pagelist);
+
+			pr_info("soft offline: %#lx: %s migration failed %d, type %lx (%pGp)\n",
+				pfn, msg_page[huge], ret, page->flags, &page->flags);
+			if (ret > 0)
+				ret = -EBUSY;
+		}
+	} else {
+		pr_info("soft offline: %#lx: %s isolation failed, page count %d, type %lx (%pGp)\n",
+			pfn, msg_page[huge], page_count(page), page->flags, &page->flags);
+		ret = -EBUSY;
+	}
+	return ret;
+}
+
+static int soft_offline_in_use_page(struct page *page)
+{
+	struct page *hpage = compound_head(page);
+
+	if (!PageHuge(page) && PageTransHuge(hpage))
+		if (try_to_split_thp_page(page, "soft offline") < 0)
+			return -EBUSY;
+	return __soft_offline_page(page);
+}
+
+static void put_ref_page(struct page *page)
+{
+	if (page)
+		put_page(page);
+}
+
+/**
+ * soft_offline_page - Soft offline a page.
+ * @pfn: pfn to soft-offline
+ * @flags: flags. Same as memory_failure().
+ *
+ * Returns 0 on success, otherwise negated errno.
+ *
+ * Soft offline a page, by migration or invalidation,
+ * without killing anything. This is for the case when
+ * a page is not corrupted yet (so it's still valid to access),
+ * but has had a number of corrected errors and is better taken
+ * out.
+ *
+ * The actual policy on when to do that is maintained by
+ * user space.
+ *
+ * This should never impact any application or cause data loss,
+ * however it might take some time.
+ *
+ * This is not a 100% solution for all memory, but tries to be
+ * ``good enough'' for the majority of memory.
+ */
+int soft_offline_page(unsigned long pfn, int flags)
+{
+	int ret;
+	bool try_again = true;
+	struct page *page, *ref_page = NULL;
+
+	WARN_ON_ONCE(!pfn_valid(pfn) && (flags & MF_COUNT_INCREASED));
+
+	if (!pfn_valid(pfn))
+		return -ENXIO;
+	if (flags & MF_COUNT_INCREASED)
+		ref_page = pfn_to_page(pfn);
+
+	/* Only online pages can be soft-offlined (esp., not ZONE_DEVICE). */
+	page = pfn_to_online_page(pfn);
+	if (!page) {
+		put_ref_page(ref_page);
+		return -EIO;
+	}
+
+	if (PageHWPoison(page)) {
+		pr_info("%s: %#lx page already poisoned\n", __func__, pfn);
+		put_ref_page(ref_page);
+		return 0;
+	}
+
+retry:
+	get_online_mems();
+	ret = get_any_page(page, flags);
+	put_online_mems();
+
+	if (ret > 0) {
+		ret = soft_offline_in_use_page(page);
+	} else if (ret == 0) {
+		if (!page_handle_poison(page, true, false)) {
+			if (try_again) {
+				try_again = false;
+				flags &= ~MF_COUNT_INCREASED;
+				goto retry;
+			}
+			ret = -EBUSY;
+		}
+	} else if (ret == -EIO) {
+		pr_info("%s: %#lx: unknown page type: %lx (%pGp)\n",
+			 __func__, pfn, page->flags, &page->flags);
+	}
+
+	return ret;
+}