Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 3402 insertions, 0 deletions

diff --git a/mm/gup.c b/mm/gup.c
new file mode 100644
index 0000000000..2f8a2d89fd
--- /dev/null
+++ b/mm/gup.c
@@ -0,0 +1,3402 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/err.h>
+#include <linux/spinlock.h>
+
+#include <linux/mm.h>
+#include <linux/memremap.h>
+#include <linux/pagemap.h>
+#include <linux/rmap.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/secretmem.h>
+
+#include <linux/sched/signal.h>
+#include <linux/rwsem.h>
+#include <linux/hugetlb.h>
+#include <linux/migrate.h>
+#include <linux/mm_inline.h>
+#include <linux/sched/mm.h>
+#include <linux/shmem_fs.h>
+
+#include <asm/mmu_context.h>
+#include <asm/tlbflush.h>
+
+#include "internal.h"
+
+struct follow_page_context {
+	struct dev_pagemap *pgmap;
+	unsigned int page_mask;
+};
+
+static inline void sanity_check_pinned_pages(struct page **pages,
+					     unsigned long npages)
+{
+	if (!IS_ENABLED(CONFIG_DEBUG_VM))
+		return;
+
+	/*
+	 * We only pin anonymous pages if they are exclusive. Once pinned, we
+	 * can no longer turn them possibly shared and PageAnonExclusive() will
+	 * stick around until the page is freed.
+	 *
+	 * We'd like to verify that our pinned anonymous pages are still mapped
+	 * exclusively. The issue with anon THP is that we don't know how
+	 * they are/were mapped when pinning them. However, for anon
+	 * THP we can assume that either the given page (PTE-mapped THP) or
+	 * the head page (PMD-mapped THP) should be PageAnonExclusive(). If
+	 * neither is the case, there is certainly something wrong.
+	 */
+	for (; npages; npages--, pages++) {
+		struct page *page = *pages;
+		struct folio *folio = page_folio(page);
+
+		if (is_zero_page(page) ||
+		    !folio_test_anon(folio))
+			continue;
+		if (!folio_test_large(folio) || folio_test_hugetlb(folio))
+			VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page), page);
+		else
+			/* Either a PTE-mapped or a PMD-mapped THP. */
+			VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page) &&
+				       !PageAnonExclusive(page), page);
+	}
+}
+
+/*
+ * Return the folio with ref appropriately incremented,
+ * or NULL if that failed.
+ */
+static inline struct folio *try_get_folio(struct page *page, int refs)
+{
+	struct folio *folio;
+
+retry:
+	folio = page_folio(page);
+	if (WARN_ON_ONCE(folio_ref_count(folio) < 0))
+		return NULL;
+	if (unlikely(!folio_ref_try_add_rcu(folio, refs)))
+		return NULL;
+
+	/*
+	 * At this point we have a stable reference to the folio; but it
+	 * could be that between calling page_folio() and the refcount
+	 * increment, the folio was split, in which case we'd end up
+	 * holding a reference on a folio that has nothing to do with the page
+	 * we were given anymore.
+	 * So now that the folio is stable, recheck that the page still
+	 * belongs to this folio.
+	 */
+	if (unlikely(page_folio(page) != folio)) {
+		if (!put_devmap_managed_page_refs(&folio->page, refs))
+			folio_put_refs(folio, refs);
+		goto retry;
+	}
+
+	return folio;
+}
+
+/**
+ * try_grab_folio() - Attempt to get or pin a folio.
+ * @page:  pointer to page to be grabbed
+ * @refs:  the value to (effectively) add to the folio's refcount
+ * @flags: gup flags: these are the FOLL_* flag values.
+ *
+ * "grab" names in this file mean, "look at flags to decide whether to use
+ * FOLL_PIN or FOLL_GET behavior, when incrementing the folio's refcount.
+ *
+ * Either FOLL_PIN or FOLL_GET (or neither) must be set, but not both at the
+ * same time. (That's true throughout the get_user_pages*() and
+ * pin_user_pages*() APIs.) Cases:
+ *
+ *    FOLL_GET: folio's refcount will be incremented by @refs.
+ *
+ *    FOLL_PIN on large folios: folio's refcount will be incremented by
+ *    @refs, and its pincount will be incremented by @refs.
+ *
+ *    FOLL_PIN on single-page folios: folio's refcount will be incremented by
+ *    @refs * GUP_PIN_COUNTING_BIAS.
+ *
+ * Return: The folio containing @page (with refcount appropriately
+ * incremented) for success, or NULL upon failure. If neither FOLL_GET
+ * nor FOLL_PIN was set, that's considered failure, and furthermore,
+ * a likely bug in the caller, so a warning is also emitted.
+ */
+struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags)
+{
+	struct folio *folio;
+
+	if (WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) == 0))
+		return NULL;
+
+	if (unlikely(!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(page)))
+		return NULL;
+
+	if (flags & FOLL_GET)
+		return try_get_folio(page, refs);
+
+	/* FOLL_PIN is set */
+
+	/*
+	 * Don't take a pin on the zero page - it's not going anywhere
+	 * and it is used in a *lot* of places.
+	 */
+	if (is_zero_page(page))
+		return page_folio(page);
+
+	folio = try_get_folio(page, refs);
+	if (!folio)
+		return NULL;
+
+	/*
+	 * Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a
+	 * right zone, so fail and let the caller fall back to the slow
+	 * path.
+	 */
+	if (unlikely((flags & FOLL_LONGTERM) &&
+		     !folio_is_longterm_pinnable(folio))) {
+		if (!put_devmap_managed_page_refs(&folio->page, refs))
+			folio_put_refs(folio, refs);
+		return NULL;
+	}
+
+	/*
+	 * When pinning a large folio, use an exact count to track it.
+	 *
+	 * However, be sure to *also* increment the normal folio
+	 * refcount field at least once, so that the folio really
+	 * is pinned.  That's why the refcount from the earlier
+	 * try_get_folio() is left intact.
+	 */
+	if (folio_test_large(folio))
+		atomic_add(refs, &folio->_pincount);
+	else
+		folio_ref_add(folio,
+				refs * (GUP_PIN_COUNTING_BIAS - 1));
+	/*
+	 * Adjust the pincount before re-checking the PTE for changes.
+	 * This is essentially a smp_mb() and is paired with a memory
+	 * barrier in page_try_share_anon_rmap().
+	 */
+	smp_mb__after_atomic();
+
+	node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, refs);
+
+	return folio;
+}
+
+static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
+{
+	if (flags & FOLL_PIN) {
+		if (is_zero_folio(folio))
+			return;
+		node_stat_mod_folio(folio, NR_FOLL_PIN_RELEASED, refs);
+		if (folio_test_large(folio))
+			atomic_sub(refs, &folio->_pincount);
+		else
+			refs *= GUP_PIN_COUNTING_BIAS;
+	}
+
+	if (!put_devmap_managed_page_refs(&folio->page, refs))
+		folio_put_refs(folio, refs);
+}
+
+/**
+ * try_grab_page() - elevate a page's refcount by a flag-dependent amount
+ * @page:    pointer to page to be grabbed
+ * @flags:   gup flags: these are the FOLL_* flag values.
+ *
+ * This might not do anything at all, depending on the flags argument.
+ *
+ * "grab" names in this file mean, "look at flags to decide whether to use
+ * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount.
+ *
+ * Either FOLL_PIN or FOLL_GET (or neither) may be set, but not both at the same
+ * time. Cases: please see the try_grab_folio() documentation, with
+ * "refs=1".
+ *
+ * Return: 0 for success, or if no action was required (if neither FOLL_PIN
+ * nor FOLL_GET was set, nothing is done). A negative error code for failure:
+ *
+ *   -ENOMEM		FOLL_GET or FOLL_PIN was set, but the page could not
+ *			be grabbed.
+ */
+int __must_check try_grab_page(struct page *page, unsigned int flags)
+{
+	struct folio *folio = page_folio(page);
+
+	if (WARN_ON_ONCE(folio_ref_count(folio) <= 0))
+		return -ENOMEM;
+
+	if (unlikely(!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(page)))
+		return -EREMOTEIO;
+
+	if (flags & FOLL_GET)
+		folio_ref_inc(folio);
+	else if (flags & FOLL_PIN) {
+		/*
+		 * Don't take a pin on the zero page - it's not going anywhere
+		 * and it is used in a *lot* of places.
+		 */
+		if (is_zero_page(page))
+			return 0;
+
+		/*
+		 * Similar to try_grab_folio(): be sure to *also*
+		 * increment the normal page refcount field at least once,
+		 * so that the page really is pinned.
+		 */
+		if (folio_test_large(folio)) {
+			folio_ref_add(folio, 1);
+			atomic_add(1, &folio->_pincount);
+		} else {
+			folio_ref_add(folio, GUP_PIN_COUNTING_BIAS);
+		}
+
+		node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, 1);
+	}
+
+	return 0;
+}
+
+/**
+ * unpin_user_page() - release a dma-pinned page
+ * @page:            pointer to page to be released
+ *
+ * Pages that were pinned via pin_user_pages*() must be released via either
+ * unpin_user_page(), or one of the unpin_user_pages*() routines. This is so
+ * that such pages can be separately tracked and uniquely handled. In
+ * particular, interactions with RDMA and filesystems need special handling.
+ */
+void unpin_user_page(struct page *page)
+{
+	sanity_check_pinned_pages(&page, 1);
+	gup_put_folio(page_folio(page), 1, FOLL_PIN);
+}
+EXPORT_SYMBOL(unpin_user_page);
+
+/**
+ * folio_add_pin - Try to get an additional pin on a pinned folio
+ * @folio: The folio to be pinned
+ *
+ * Get an additional pin on a folio we already have a pin on.  Makes no change
+ * if the folio is a zero_page.
+ */
+void folio_add_pin(struct folio *folio)
+{
+	if (is_zero_folio(folio))
+		return;
+
+	/*
+	 * Similar to try_grab_folio(): be sure to *also* increment the normal
+	 * page refcount field at least once, so that the page really is
+	 * pinned.
+	 */
+	if (folio_test_large(folio)) {
+		WARN_ON_ONCE(atomic_read(&folio->_pincount) < 1);
+		folio_ref_inc(folio);
+		atomic_inc(&folio->_pincount);
+	} else {
+		WARN_ON_ONCE(folio_ref_count(folio) < GUP_PIN_COUNTING_BIAS);
+		folio_ref_add(folio, GUP_PIN_COUNTING_BIAS);
+	}
+}
+
+static inline struct folio *gup_folio_range_next(struct page *start,
+		unsigned long npages, unsigned long i, unsigned int *ntails)
+{
+	struct page *next = nth_page(start, i);
+	struct folio *folio = page_folio(next);
+	unsigned int nr = 1;
+
+	if (folio_test_large(folio))
+		nr = min_t(unsigned int, npages - i,
+			   folio_nr_pages(folio) - folio_page_idx(folio, next));
+
+	*ntails = nr;
+	return folio;
+}
+
+static inline struct folio *gup_folio_next(struct page **list,
+		unsigned long npages, unsigned long i, unsigned int *ntails)
+{
+	struct folio *folio = page_folio(list[i]);
+	unsigned int nr;
+
+	for (nr = i + 1; nr < npages; nr++) {
+		if (page_folio(list[nr]) != folio)
+			break;
+	}
+
+	*ntails = nr - i;
+	return folio;
+}
+
+/**
+ * unpin_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
+ * @pages:  array of pages to be maybe marked dirty, and definitely released.
+ * @npages: number of pages in the @pages array.
+ * @make_dirty: whether to mark the pages dirty
+ *
+ * "gup-pinned page" refers to a page that has had one of the get_user_pages()
+ * variants called on that page.
+ *
+ * For each page in the @pages array, make that page (or its head page, if a
+ * compound page) dirty, if @make_dirty is true, and if the page was previously
+ * listed as clean. In any case, releases all pages using unpin_user_page(),
+ * possibly via unpin_user_pages(), for the non-dirty case.
+ *
+ * Please see the unpin_user_page() documentation for details.
+ *
+ * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
+ * required, then the caller should a) verify that this is really correct,
+ * because _lock() is usually required, and b) hand code it:
+ * set_page_dirty_lock(), unpin_user_page().
+ *
+ */
+void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
+				 bool make_dirty)
+{
+	unsigned long i;
+	struct folio *folio;
+	unsigned int nr;
+
+	if (!make_dirty) {
+		unpin_user_pages(pages, npages);
+		return;
+	}
+
+	sanity_check_pinned_pages(pages, npages);
+	for (i = 0; i < npages; i += nr) {
+		folio = gup_folio_next(pages, npages, i, &nr);
+		/*
+		 * Checking PageDirty at this point may race with
+		 * clear_page_dirty_for_io(), but that's OK. Two key
+		 * cases:
+		 *
+		 * 1) This code sees the page as already dirty, so it
+		 * skips the call to set_page_dirty(). That could happen
+		 * because clear_page_dirty_for_io() called
+		 * page_mkclean(), followed by set_page_dirty().
+		 * However, now the page is going to get written back,
+		 * which meets the original intention of setting it
+		 * dirty, so all is well: clear_page_dirty_for_io() goes
+		 * on to call TestClearPageDirty(), and write the page
+		 * back.
+		 *
+		 * 2) This code sees the page as clean, so it calls
+		 * set_page_dirty(). The page stays dirty, despite being
+		 * written back, so it gets written back again in the
+		 * next writeback cycle. This is harmless.
+		 */
+		if (!folio_test_dirty(folio)) {
+			folio_lock(folio);
+			folio_mark_dirty(folio);
+			folio_unlock(folio);
+		}
+		gup_put_folio(folio, nr, FOLL_PIN);
+	}
+}
+EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
+
+/**
+ * unpin_user_page_range_dirty_lock() - release and optionally dirty
+ * gup-pinned page range
+ *
+ * @page:  the starting page of a range maybe marked dirty, and definitely released.
+ * @npages: number of consecutive pages to release.
+ * @make_dirty: whether to mark the pages dirty
+ *
+ * "gup-pinned page range" refers to a range of pages that has had one of the
+ * pin_user_pages() variants called on that page.
+ *
+ * For the page ranges defined by [page .. page+npages], make that range (or
+ * its head pages, if a compound page) dirty, if @make_dirty is true, and if the
+ * page range was previously listed as clean.
+ *
+ * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
+ * required, then the caller should a) verify that this is really correct,
+ * because _lock() is usually required, and b) hand code it:
+ * set_page_dirty_lock(), unpin_user_page().
+ *
+ */
+void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
+				      bool make_dirty)
+{
+	unsigned long i;
+	struct folio *folio;
+	unsigned int nr;
+
+	for (i = 0; i < npages; i += nr) {
+		folio = gup_folio_range_next(page, npages, i, &nr);
+		if (make_dirty && !folio_test_dirty(folio)) {
+			folio_lock(folio);
+			folio_mark_dirty(folio);
+			folio_unlock(folio);
+		}
+		gup_put_folio(folio, nr, FOLL_PIN);
+	}
+}
+EXPORT_SYMBOL(unpin_user_page_range_dirty_lock);
+
+static void unpin_user_pages_lockless(struct page **pages, unsigned long npages)
+{
+	unsigned long i;
+	struct folio *folio;
+	unsigned int nr;
+
+	/*
+	 * Don't perform any sanity checks because we might have raced with
+	 * fork() and some anonymous pages might now actually be shared --
+	 * which is why we're unpinning after all.
+	 */
+	for (i = 0; i < npages; i += nr) {
+		folio = gup_folio_next(pages, npages, i, &nr);
+		gup_put_folio(folio, nr, FOLL_PIN);
+	}
+}
+
+/**
+ * unpin_user_pages() - release an array of gup-pinned pages.
+ * @pages:  array of pages to be marked dirty and released.
+ * @npages: number of pages in the @pages array.
+ *
+ * For each page in the @pages array, release the page using unpin_user_page().
+ *
+ * Please see the unpin_user_page() documentation for details.
+ */
+void unpin_user_pages(struct page **pages, unsigned long npages)
+{
+	unsigned long i;
+	struct folio *folio;
+	unsigned int nr;
+
+	/*
+	 * If this WARN_ON() fires, then the system *might* be leaking pages (by
+	 * leaving them pinned), but probably not. More likely, gup/pup returned
+	 * a hard -ERRNO error to the caller, who erroneously passed it here.
+	 */
+	if (WARN_ON(IS_ERR_VALUE(npages)))
+		return;
+
+	sanity_check_pinned_pages(pages, npages);
+	for (i = 0; i < npages; i += nr) {
+		folio = gup_folio_next(pages, npages, i, &nr);
+		gup_put_folio(folio, nr, FOLL_PIN);
+	}
+}
+EXPORT_SYMBOL(unpin_user_pages);
+
+/*
+ * Set the MMF_HAS_PINNED if not set yet; after set it'll be there for the mm's
+ * lifecycle.  Avoid setting the bit unless necessary, or it might cause write
+ * cache bouncing on large SMP machines for concurrent pinned gups.
+ */
+static inline void mm_set_has_pinned_flag(unsigned long *mm_flags)
+{
+	if (!test_bit(MMF_HAS_PINNED, mm_flags))
+		set_bit(MMF_HAS_PINNED, mm_flags);
+}
+
+#ifdef CONFIG_MMU
+static struct page *no_page_table(struct vm_area_struct *vma,
+		unsigned int flags)
+{
+	/*
+	 * When core dumping an enormous anonymous area that nobody
+	 * has touched so far, we don't want to allocate unnecessary pages or
+	 * page tables.  Return error instead of NULL to skip handle_mm_fault,
+	 * then get_dump_page() will return NULL to leave a hole in the dump.
+	 * But we can only make this optimization where a hole would surely
+	 * be zero-filled if handle_mm_fault() actually did handle it.
+	 */
+	if ((flags & FOLL_DUMP) &&
+			(vma_is_anonymous(vma) || !vma->vm_ops->fault))
+		return ERR_PTR(-EFAULT);
+	return NULL;
+}
+
+static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
+		pte_t *pte, unsigned int flags)
+{
+	if (flags & FOLL_TOUCH) {
+		pte_t orig_entry = ptep_get(pte);
+		pte_t entry = orig_entry;
+
+		if (flags & FOLL_WRITE)
+			entry = pte_mkdirty(entry);
+		entry = pte_mkyoung(entry);
+
+		if (!pte_same(orig_entry, entry)) {
+			set_pte_at(vma->vm_mm, address, pte, entry);
+			update_mmu_cache(vma, address, pte);
+		}
+	}
+
+	/* Proper page table entry exists, but no corresponding struct page */
+	return -EEXIST;
+}
+
+/* FOLL_FORCE can write to even unwritable PTEs in COW mappings. */
+static inline bool can_follow_write_pte(pte_t pte, struct page *page,
+					struct vm_area_struct *vma,
+					unsigned int flags)
+{
+	/* If the pte is writable, we can write to the page. */
+	if (pte_write(pte))
+		return true;
+
+	/* Maybe FOLL_FORCE is set to override it? */
+	if (!(flags & FOLL_FORCE))
+		return false;
+
+	/* But FOLL_FORCE has no effect on shared mappings */
+	if (vma->vm_flags & (VM_MAYSHARE | VM_SHARED))
+		return false;
+
+	/* ... or read-only private ones */
+	if (!(vma->vm_flags & VM_MAYWRITE))
+		return false;
+
+	/* ... or already writable ones that just need to take a write fault */
+	if (vma->vm_flags & VM_WRITE)
+		return false;
+
+	/*
+	 * See can_change_pte_writable(): we broke COW and could map the page
+	 * writable if we have an exclusive anonymous page ...
+	 */
+	if (!page || !PageAnon(page) || !PageAnonExclusive(page))
+		return false;
+
+	/* ... and a write-fault isn't required for other reasons. */
+	if (vma_soft_dirty_enabled(vma) && !pte_soft_dirty(pte))
+		return false;
+	return !userfaultfd_pte_wp(vma, pte);
+}
+
+static struct page *follow_page_pte(struct vm_area_struct *vma,
+		unsigned long address, pmd_t *pmd, unsigned int flags,
+		struct dev_pagemap **pgmap)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	struct page *page;
+	spinlock_t *ptl;
+	pte_t *ptep, pte;
+	int ret;
+
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
+			 (FOLL_PIN | FOLL_GET)))
+		return ERR_PTR(-EINVAL);
+
+	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
+	if (!ptep)
+		return no_page_table(vma, flags);
+	pte = ptep_get(ptep);
+	if (!pte_present(pte))
+		goto no_page;
+	if (pte_protnone(pte) && !gup_can_follow_protnone(vma, flags))
+		goto no_page;
+
+	page = vm_normal_page(vma, address, pte);
+
+	/*
+	 * We only care about anon pages in can_follow_write_pte() and don't
+	 * have to worry about pte_devmap() because they are never anon.
+	 */
+	if ((flags & FOLL_WRITE) &&
+	    !can_follow_write_pte(pte, page, vma, flags)) {
+		page = NULL;
+		goto out;
+	}
+
+	if (!page && pte_devmap(pte) && (flags & (FOLL_GET | FOLL_PIN))) {
+		/*
+		 * Only return device mapping pages in the FOLL_GET or FOLL_PIN
+		 * case since they are only valid while holding the pgmap
+		 * reference.
+		 */
+		*pgmap = get_dev_pagemap(pte_pfn(pte), *pgmap);
+		if (*pgmap)
+			page = pte_page(pte);
+		else
+			goto no_page;
+	} else if (unlikely(!page)) {
+		if (flags & FOLL_DUMP) {
+			/* Avoid special (like zero) pages in core dumps */
+			page = ERR_PTR(-EFAULT);
+			goto out;
+		}
+
+		if (is_zero_pfn(pte_pfn(pte))) {
+			page = pte_page(pte);
+		} else {
+			ret = follow_pfn_pte(vma, address, ptep, flags);
+			page = ERR_PTR(ret);
+			goto out;
+		}
+	}
+
+	if (!pte_write(pte) && gup_must_unshare(vma, flags, page)) {
+		page = ERR_PTR(-EMLINK);
+		goto out;
+	}
+
+	VM_BUG_ON_PAGE((flags & FOLL_PIN) && PageAnon(page) &&
+		       !PageAnonExclusive(page), page);
+
+	/* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */
+	ret = try_grab_page(page, flags);
+	if (unlikely(ret)) {
+		page = ERR_PTR(ret);
+		goto out;
+	}
+
+	/*
+	 * We need to make the page accessible if and only if we are going
+	 * to access its content (the FOLL_PIN case).  Please see
+	 * Documentation/core-api/pin_user_pages.rst for details.
+	 */
+	if (flags & FOLL_PIN) {
+		ret = arch_make_page_accessible(page);
+		if (ret) {
+			unpin_user_page(page);
+			page = ERR_PTR(ret);
+			goto out;
+		}
+	}
+	if (flags & FOLL_TOUCH) {
+		if ((flags & FOLL_WRITE) &&
+		    !pte_dirty(pte) && !PageDirty(page))
+			set_page_dirty(page);
+		/*
+		 * pte_mkyoung() would be more correct here, but atomic care
+		 * is needed to avoid losing the dirty bit: it is easier to use
+		 * mark_page_accessed().
+		 */
+		mark_page_accessed(page);
+	}
+out:
+	pte_unmap_unlock(ptep, ptl);
+	return page;
+no_page:
+	pte_unmap_unlock(ptep, ptl);
+	if (!pte_none(pte))
+		return NULL;
+	return no_page_table(vma, flags);
+}
+
+static struct page *follow_pmd_mask(struct vm_area_struct *vma,
+				    unsigned long address, pud_t *pudp,
+				    unsigned int flags,
+				    struct follow_page_context *ctx)
+{
+	pmd_t *pmd, pmdval;
+	spinlock_t *ptl;
+	struct page *page;
+	struct mm_struct *mm = vma->vm_mm;
+
+	pmd = pmd_offset(pudp, address);
+	pmdval = pmdp_get_lockless(pmd);
+	if (pmd_none(pmdval))
+		return no_page_table(vma, flags);
+	if (!pmd_present(pmdval))
+		return no_page_table(vma, flags);
+	if (pmd_devmap(pmdval)) {
+		ptl = pmd_lock(mm, pmd);
+		page = follow_devmap_pmd(vma, address, pmd, flags, &ctx->pgmap);
+		spin_unlock(ptl);
+		if (page)
+			return page;
+	}
+	if (likely(!pmd_trans_huge(pmdval)))
+		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
+
+	if (pmd_protnone(pmdval) && !gup_can_follow_protnone(vma, flags))
+		return no_page_table(vma, flags);
+
+	ptl = pmd_lock(mm, pmd);
+	if (unlikely(!pmd_present(*pmd))) {
+		spin_unlock(ptl);
+		return no_page_table(vma, flags);
+	}
+	if (unlikely(!pmd_trans_huge(*pmd))) {
+		spin_unlock(ptl);
+		return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
+	}
+	if (flags & FOLL_SPLIT_PMD) {
+		spin_unlock(ptl);
+		split_huge_pmd(vma, pmd, address);
+		/* If pmd was left empty, stuff a page table in there quickly */
+		return pte_alloc(mm, pmd) ? ERR_PTR(-ENOMEM) :
+			follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
+	}
+	page = follow_trans_huge_pmd(vma, address, pmd, flags);
+	spin_unlock(ptl);
+	ctx->page_mask = HPAGE_PMD_NR - 1;
+	return page;
+}
+
+static struct page *follow_pud_mask(struct vm_area_struct *vma,
+				    unsigned long address, p4d_t *p4dp,
+				    unsigned int flags,
+				    struct follow_page_context *ctx)
+{
+	pud_t *pud;
+	spinlock_t *ptl;
+	struct page *page;
+	struct mm_struct *mm = vma->vm_mm;
+
+	pud = pud_offset(p4dp, address);
+	if (pud_none(*pud))
+		return no_page_table(vma, flags);
+	if (pud_devmap(*pud)) {
+		ptl = pud_lock(mm, pud);
+		page = follow_devmap_pud(vma, address, pud, flags, &ctx->pgmap);
+		spin_unlock(ptl);
+		if (page)
+			return page;
+	}
+	if (unlikely(pud_bad(*pud)))
+		return no_page_table(vma, flags);
+
+	return follow_pmd_mask(vma, address, pud, flags, ctx);
+}
+
+static struct page *follow_p4d_mask(struct vm_area_struct *vma,
+				    unsigned long address, pgd_t *pgdp,
+				    unsigned int flags,
+				    struct follow_page_context *ctx)
+{
+	p4d_t *p4d;
+
+	p4d = p4d_offset(pgdp, address);
+	if (p4d_none(*p4d))
+		return no_page_table(vma, flags);
+	BUILD_BUG_ON(p4d_huge(*p4d));
+	if (unlikely(p4d_bad(*p4d)))
+		return no_page_table(vma, flags);
+
+	return follow_pud_mask(vma, address, p4d, flags, ctx);
+}
+
+/**
+ * follow_page_mask - look up a page descriptor from a user-virtual address
+ * @vma: vm_area_struct mapping @address
+ * @address: virtual address to look up
+ * @flags: flags modifying lookup behaviour
+ * @ctx: contains dev_pagemap for %ZONE_DEVICE memory pinning and a
+ *       pointer to output page_mask
+ *
+ * @flags can have FOLL_ flags set, defined in <linux/mm.h>
+ *
+ * When getting pages from ZONE_DEVICE memory, the @ctx->pgmap caches
+ * the device's dev_pagemap metadata to avoid repeating expensive lookups.
+ *
+ * When getting an anonymous page and the caller has to trigger unsharing
+ * of a shared anonymous page first, -EMLINK is returned. The caller should
+ * trigger a fault with FAULT_FLAG_UNSHARE set. Note that unsharing is only
+ * relevant with FOLL_PIN and !FOLL_WRITE.
+ *
+ * On output, the @ctx->page_mask is set according to the size of the page.
+ *
+ * Return: the mapped (struct page *), %NULL if no mapping exists, or
+ * an error pointer if there is a mapping to something not represented
+ * by a page descriptor (see also vm_normal_page()).
+ */
+static struct page *follow_page_mask(struct vm_area_struct *vma,
+			      unsigned long address, unsigned int flags,
+			      struct follow_page_context *ctx)
+{
+	pgd_t *pgd;
+	struct mm_struct *mm = vma->vm_mm;
+
+	ctx->page_mask = 0;
+
+	/*
+	 * Call hugetlb_follow_page_mask for hugetlb vmas as it will use
+	 * special hugetlb page table walking code.  This eliminates the
+	 * need to check for hugetlb entries in the general walking code.
+	 */
+	if (is_vm_hugetlb_page(vma))
+		return hugetlb_follow_page_mask(vma, address, flags,
+						&ctx->page_mask);
+
+	pgd = pgd_offset(mm, address);
+
+	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+		return no_page_table(vma, flags);
+
+	return follow_p4d_mask(vma, address, pgd, flags, ctx);
+}
+
+struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
+			 unsigned int foll_flags)
+{
+	struct follow_page_context ctx = { NULL };
+	struct page *page;
+
+	if (vma_is_secretmem(vma))
+		return NULL;
+
+	if (WARN_ON_ONCE(foll_flags & FOLL_PIN))
+		return NULL;
+
+	/*
+	 * We never set FOLL_HONOR_NUMA_FAULT because callers don't expect
+	 * to fail on PROT_NONE-mapped pages.
+	 */
+	page = follow_page_mask(vma, address, foll_flags, &ctx);
+	if (ctx.pgmap)
+		put_dev_pagemap(ctx.pgmap);
+	return page;
+}
+
+static int get_gate_page(struct mm_struct *mm, unsigned long address,
+		unsigned int gup_flags, struct vm_area_struct **vma,
+		struct page **page)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+	pte_t entry;
+	int ret = -EFAULT;
+
+	/* user gate pages are read-only */
+	if (gup_flags & FOLL_WRITE)
+		return -EFAULT;
+	if (address > TASK_SIZE)
+		pgd = pgd_offset_k(address);
+	else
+		pgd = pgd_offset_gate(mm, address);
+	if (pgd_none(*pgd))
+		return -EFAULT;
+	p4d = p4d_offset(pgd, address);
+	if (p4d_none(*p4d))
+		return -EFAULT;
+	pud = pud_offset(p4d, address);
+	if (pud_none(*pud))
+		return -EFAULT;
+	pmd = pmd_offset(pud, address);
+	if (!pmd_present(*pmd))
+		return -EFAULT;
+	pte = pte_offset_map(pmd, address);
+	if (!pte)
+		return -EFAULT;
+	entry = ptep_get(pte);
+	if (pte_none(entry))
+		goto unmap;
+	*vma = get_gate_vma(mm);
+	if (!page)
+		goto out;
+	*page = vm_normal_page(*vma, address, entry);
+	if (!*page) {
+		if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(entry)))
+			goto unmap;
+		*page = pte_page(entry);
+	}
+	ret = try_grab_page(*page, gup_flags);
+	if (unlikely(ret))
+		goto unmap;
+out:
+	ret = 0;
+unmap:
+	pte_unmap(pte);
+	return ret;
+}
+
+/*
+ * mmap_lock must be held on entry.  If @flags has FOLL_UNLOCKABLE but not
+ * FOLL_NOWAIT, the mmap_lock may be released.  If it is, *@locked will be set
+ * to 0 and -EBUSY returned.
+ */
+static int faultin_page(struct vm_area_struct *vma,
+		unsigned long address, unsigned int *flags, bool unshare,
+		int *locked)
+{
+	unsigned int fault_flags = 0;
+	vm_fault_t ret;
+
+	if (*flags & FOLL_NOFAULT)
+		return -EFAULT;
+	if (*flags & FOLL_WRITE)
+		fault_flags |= FAULT_FLAG_WRITE;
+	if (*flags & FOLL_REMOTE)
+		fault_flags |= FAULT_FLAG_REMOTE;
+	if (*flags & FOLL_UNLOCKABLE) {
+		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+		/*
+		 * FAULT_FLAG_INTERRUPTIBLE is opt-in. GUP callers must set
+		 * FOLL_INTERRUPTIBLE to enable FAULT_FLAG_INTERRUPTIBLE.
+		 * That's because some callers may not be prepared to
+		 * handle early exits caused by non-fatal signals.
+		 */
+		if (*flags & FOLL_INTERRUPTIBLE)
+			fault_flags |= FAULT_FLAG_INTERRUPTIBLE;
+	}
+	if (*flags & FOLL_NOWAIT)
+		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
+	if (*flags & FOLL_TRIED) {
+		/*
+		 * Note: FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_TRIED
+		 * can co-exist
+		 */
+		fault_flags |= FAULT_FLAG_TRIED;
+	}
+	if (unshare) {
+		fault_flags |= FAULT_FLAG_UNSHARE;
+		/* FAULT_FLAG_WRITE and FAULT_FLAG_UNSHARE are incompatible */
+		VM_BUG_ON(fault_flags & FAULT_FLAG_WRITE);
+	}
+
+	ret = handle_mm_fault(vma, address, fault_flags, NULL);
+
+	if (ret & VM_FAULT_COMPLETED) {
+		/*
+		 * With FAULT_FLAG_RETRY_NOWAIT we'll never release the
+		 * mmap lock in the page fault handler. Sanity check this.
+		 */
+		WARN_ON_ONCE(fault_flags & FAULT_FLAG_RETRY_NOWAIT);
+		*locked = 0;
+
+		/*
+		 * We should do the same as VM_FAULT_RETRY, but let's not
+		 * return -EBUSY since that's not reflecting the reality of
+		 * what has happened - we've just fully completed a page
+		 * fault, with the mmap lock released.  Use -EAGAIN to show
+		 * that we want to take the mmap lock _again_.
+		 */
+		return -EAGAIN;
+	}
+
+	if (ret & VM_FAULT_ERROR) {
+		int err = vm_fault_to_errno(ret, *flags);
+
+		if (err)
+			return err;
+		BUG();
+	}
+
+	if (ret & VM_FAULT_RETRY) {
+		if (!(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
+			*locked = 0;
+		return -EBUSY;
+	}
+
+	return 0;
+}
+
+/*
+ * Writing to file-backed mappings which require folio dirty tracking using GUP
+ * is a fundamentally broken operation, as kernel write access to GUP mappings
+ * do not adhere to the semantics expected by a file system.
+ *
+ * Consider the following scenario:-
+ *
+ * 1. A folio is written to via GUP which write-faults the memory, notifying
+ *    the file system and dirtying the folio.
+ * 2. Later, writeback is triggered, resulting in the folio being cleaned and
+ *    the PTE being marked read-only.
+ * 3. The GUP caller writes to the folio, as it is mapped read/write via the
+ *    direct mapping.
+ * 4. The GUP caller, now done with the page, unpins it and sets it dirty
+ *    (though it does not have to).
+ *
+ * This results in both data being written to a folio without writenotify, and
+ * the folio being dirtied unexpectedly (if the caller decides to do so).
+ */
+static bool writable_file_mapping_allowed(struct vm_area_struct *vma,
+					  unsigned long gup_flags)
+{
+	/*
+	 * If we aren't pinning then no problematic write can occur. A long term
+	 * pin is the most egregious case so this is the case we disallow.
+	 */
+	if ((gup_flags & (FOLL_PIN | FOLL_LONGTERM)) !=
+	    (FOLL_PIN | FOLL_LONGTERM))
+		return true;
+
+	/*
+	 * If the VMA does not require dirty tracking then no problematic write
+	 * can occur either.
+	 */
+	return !vma_needs_dirty_tracking(vma);
+}
+
+static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
+{
+	vm_flags_t vm_flags = vma->vm_flags;
+	int write = (gup_flags & FOLL_WRITE);
+	int foreign = (gup_flags & FOLL_REMOTE);
+	bool vma_anon = vma_is_anonymous(vma);
+
+	if (vm_flags & (VM_IO | VM_PFNMAP))
+		return -EFAULT;
+
+	if ((gup_flags & FOLL_ANON) && !vma_anon)
+		return -EFAULT;
+
+	if ((gup_flags & FOLL_LONGTERM) && vma_is_fsdax(vma))
+		return -EOPNOTSUPP;
+
+	if (vma_is_secretmem(vma))
+		return -EFAULT;
+
+	if (write) {
+		if (!vma_anon &&
+		    !writable_file_mapping_allowed(vma, gup_flags))
+			return -EFAULT;
+
+		if (!(vm_flags & VM_WRITE) || (vm_flags & VM_SHADOW_STACK)) {
+			if (!(gup_flags & FOLL_FORCE))
+				return -EFAULT;
+			/* hugetlb does not support FOLL_FORCE|FOLL_WRITE. */
+			if (is_vm_hugetlb_page(vma))
+				return -EFAULT;
+			/*
+			 * We used to let the write,force case do COW in a
+			 * VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
+			 * set a breakpoint in a read-only mapping of an
+			 * executable, without corrupting the file (yet only
+			 * when that file had been opened for writing!).
+			 * Anon pages in shared mappings are surprising: now
+			 * just reject it.
+			 */
+			if (!is_cow_mapping(vm_flags))
+				return -EFAULT;
+		}
+	} else if (!(vm_flags & VM_READ)) {
+		if (!(gup_flags & FOLL_FORCE))
+			return -EFAULT;
+		/*
+		 * Is there actually any vma we can reach here which does not
+		 * have VM_MAYREAD set?
+		 */
+		if (!(vm_flags & VM_MAYREAD))
+			return -EFAULT;
+	}
+	/*
+	 * gups are always data accesses, not instruction
+	 * fetches, so execute=false here
+	 */
+	if (!arch_vma_access_permitted(vma, write, false, foreign))
+		return -EFAULT;
+	return 0;
+}
+
+/*
+ * This is "vma_lookup()", but with a warning if we would have
+ * historically expanded the stack in the GUP code.
+ */
+static struct vm_area_struct *gup_vma_lookup(struct mm_struct *mm,
+	 unsigned long addr)
+{
+#ifdef CONFIG_STACK_GROWSUP
+	return vma_lookup(mm, addr);
+#else
+	static volatile unsigned long next_warn;
+	struct vm_area_struct *vma;
+	unsigned long now, next;
+
+	vma = find_vma(mm, addr);
+	if (!vma || (addr >= vma->vm_start))
+		return vma;
+
+	/* Only warn for half-way relevant accesses */
+	if (!(vma->vm_flags & VM_GROWSDOWN))
+		return NULL;
+	if (vma->vm_start - addr > 65536)
+		return NULL;
+
+	/* Let's not warn more than once an hour.. */
+	now = jiffies; next = next_warn;
+	if (next && time_before(now, next))
+		return NULL;
+	next_warn = now + 60*60*HZ;
+
+	/* Let people know things may have changed. */
+	pr_warn("GUP no longer grows the stack in %s (%d): %lx-%lx (%lx)\n",
+		current->comm, task_pid_nr(current),
+		vma->vm_start, vma->vm_end, addr);
+	dump_stack();
+	return NULL;
+#endif
+}
+
+/**
+ * __get_user_pages() - pin user pages in memory
+ * @mm:		mm_struct of target mm
+ * @start:	starting user address
+ * @nr_pages:	number of pages from start to pin
+ * @gup_flags:	flags modifying pin behaviour
+ * @pages:	array that receives pointers to the pages pinned.
+ *		Should be at least nr_pages long. Or NULL, if caller
+ *		only intends to ensure the pages are faulted in.
+ * @locked:     whether we're still with the mmap_lock held
+ *
+ * Returns either number of pages pinned (which may be less than the
+ * number requested), or an error. Details about the return value:
+ *
+ * -- If nr_pages is 0, returns 0.
+ * -- If nr_pages is >0, but no pages were pinned, returns -errno.
+ * -- If nr_pages is >0, and some pages were pinned, returns the number of
+ *    pages pinned. Again, this may be less than nr_pages.
+ * -- 0 return value is possible when the fault would need to be retried.
+ *
+ * The caller is responsible for releasing returned @pages, via put_page().
+ *
+ * Must be called with mmap_lock held.  It may be released.  See below.
+ *
+ * __get_user_pages walks a process's page tables and takes a reference to
+ * each struct page that each user address corresponds to at a given
+ * instant. That is, it takes the page that would be accessed if a user
+ * thread accesses the given user virtual address at that instant.
+ *
+ * This does not guarantee that the page exists in the user mappings when
+ * __get_user_pages returns, and there may even be a completely different
+ * page there in some cases (eg. if mmapped pagecache has been invalidated
+ * and subsequently re-faulted). However it does guarantee that the page
+ * won't be freed completely. And mostly callers simply care that the page
+ * contains data that was valid *at some point in time*. Typically, an IO
+ * or similar operation cannot guarantee anything stronger anyway because
+ * locks can't be held over the syscall boundary.
+ *
+ * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
+ * the page is written to, set_page_dirty (or set_page_dirty_lock, as
+ * appropriate) must be called after the page is finished with, and
+ * before put_page is called.
+ *
+ * If FOLL_UNLOCKABLE is set without FOLL_NOWAIT then the mmap_lock may
+ * be released. If this happens *@locked will be set to 0 on return.
+ *
+ * A caller using such a combination of @gup_flags must therefore hold the
+ * mmap_lock for reading only, and recognize when it's been released. Otherwise,
+ * it must be held for either reading or writing and will not be released.
+ *
+ * In most cases, get_user_pages or get_user_pages_fast should be used
+ * instead of __get_user_pages. __get_user_pages should be used only if
+ * you need some special @gup_flags.
+ */
+static long __get_user_pages(struct mm_struct *mm,
+		unsigned long start, unsigned long nr_pages,
+		unsigned int gup_flags, struct page **pages,
+		int *locked)
+{
+	long ret = 0, i = 0;
+	struct vm_area_struct *vma = NULL;
+	struct follow_page_context ctx = { NULL };
+
+	if (!nr_pages)
+		return 0;
+
+	start = untagged_addr_remote(mm, start);
+
+	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
+
+	do {
+		struct page *page;
+		unsigned int foll_flags = gup_flags;
+		unsigned int page_increm;
+
+		/* first iteration or cross vma bound */
+		if (!vma || start >= vma->vm_end) {
+			vma = gup_vma_lookup(mm, start);
+			if (!vma && in_gate_area(mm, start)) {
+				ret = get_gate_page(mm, start & PAGE_MASK,
+						gup_flags, &vma,
+						pages ? &page : NULL);
+				if (ret)
+					goto out;
+				ctx.page_mask = 0;
+				goto next_page;
+			}
+
+			if (!vma) {
+				ret = -EFAULT;
+				goto out;
+			}
+			ret = check_vma_flags(vma, gup_flags);
+			if (ret)
+				goto out;
+		}
+retry:
+		/*
+		 * If we have a pending SIGKILL, don't keep faulting pages and
+		 * potentially allocating memory.
+		 */
+		if (fatal_signal_pending(current)) {
+			ret = -EINTR;
+			goto out;
+		}
+		cond_resched();
+
+		page = follow_page_mask(vma, start, foll_flags, &ctx);
+		if (!page || PTR_ERR(page) == -EMLINK) {
+			ret = faultin_page(vma, start, &foll_flags,
+					   PTR_ERR(page) == -EMLINK, locked);
+			switch (ret) {
+			case 0:
+				goto retry;
+			case -EBUSY:
+			case -EAGAIN:
+				ret = 0;
+				fallthrough;
+			case -EFAULT:
+			case -ENOMEM:
+			case -EHWPOISON:
+				goto out;
+			}
+			BUG();
+		} else if (PTR_ERR(page) == -EEXIST) {
+			/*
+			 * Proper page table entry exists, but no corresponding
+			 * struct page. If the caller expects **pages to be
+			 * filled in, bail out now, because that can't be done
+			 * for this page.
+			 */
+			if (pages) {
+				ret = PTR_ERR(page);
+				goto out;
+			}
+		} else if (IS_ERR(page)) {
+			ret = PTR_ERR(page);
+			goto out;
+		}
+next_page:
+		page_increm = 1 + (~(start >> PAGE_SHIFT) & ctx.page_mask);
+		if (page_increm > nr_pages)
+			page_increm = nr_pages;
+
+		if (pages) {
+			struct page *subpage;
+			unsigned int j;
+
+			/*
+			 * This must be a large folio (and doesn't need to
+			 * be the whole folio; it can be part of it), do
+			 * the refcount work for all the subpages too.
+			 *
+			 * NOTE: here the page may not be the head page
+			 * e.g. when start addr is not thp-size aligned.
+			 * try_grab_folio() should have taken care of tail
+			 * pages.
+			 */
+			if (page_increm > 1) {
+				struct folio *folio;
+
+				/*
+				 * Since we already hold refcount on the
+				 * large folio, this should never fail.
+				 */
+				folio = try_grab_folio(page, page_increm - 1,
+						       foll_flags);
+				if (WARN_ON_ONCE(!folio)) {
+					/*
+					 * Release the 1st page ref if the
+					 * folio is problematic, fail hard.
+					 */
+					gup_put_folio(page_folio(page), 1,
+						      foll_flags);
+					ret = -EFAULT;
+					goto out;
+				}
+			}
+
+			for (j = 0; j < page_increm; j++) {
+				subpage = nth_page(page, j);
+				pages[i + j] = subpage;
+				flush_anon_page(vma, subpage, start + j * PAGE_SIZE);
+				flush_dcache_page(subpage);
+			}
+		}
+
+		i += page_increm;
+		start += page_increm * PAGE_SIZE;
+		nr_pages -= page_increm;
+	} while (nr_pages);
+out:
+	if (ctx.pgmap)
+		put_dev_pagemap(ctx.pgmap);
+	return i ? i : ret;
+}
+
+static bool vma_permits_fault(struct vm_area_struct *vma,
+			      unsigned int fault_flags)
+{
+	bool write   = !!(fault_flags & FAULT_FLAG_WRITE);
+	bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
+	vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;
+
+	if (!(vm_flags & vma->vm_flags))
+		return false;
+
+	/*
+	 * The architecture might have a hardware protection
+	 * mechanism other than read/write that can deny access.
+	 *
+	 * gup always represents data access, not instruction
+	 * fetches, so execute=false here:
+	 */
+	if (!arch_vma_access_permitted(vma, write, false, foreign))
+		return false;
+
+	return true;
+}
+
+/**
+ * fixup_user_fault() - manually resolve a user page fault
+ * @mm:		mm_struct of target mm
+ * @address:	user address
+ * @fault_flags:flags to pass down to handle_mm_fault()
+ * @unlocked:	did we unlock the mmap_lock while retrying, maybe NULL if caller
+ *		does not allow retry. If NULL, the caller must guarantee
+ *		that fault_flags does not contain FAULT_FLAG_ALLOW_RETRY.
+ *
+ * This is meant to be called in the specific scenario where for locking reasons
+ * we try to access user memory in atomic context (within a pagefault_disable()
+ * section), this returns -EFAULT, and we want to resolve the user fault before
+ * trying again.
+ *
+ * Typically this is meant to be used by the futex code.
+ *
+ * The main difference with get_user_pages() is that this function will
+ * unconditionally call handle_mm_fault() which will in turn perform all the
+ * necessary SW fixup of the dirty and young bits in the PTE, while
+ * get_user_pages() only guarantees to update these in the struct page.
+ *
+ * This is important for some architectures where those bits also gate the
+ * access permission to the page because they are maintained in software.  On
+ * such architectures, gup() will not be enough to make a subsequent access
+ * succeed.
+ *
+ * This function will not return with an unlocked mmap_lock. So it has not the
+ * same semantics wrt the @mm->mmap_lock as does filemap_fault().
+ */
+int fixup_user_fault(struct mm_struct *mm,
+		     unsigned long address, unsigned int fault_flags,
+		     bool *unlocked)
+{
+	struct vm_area_struct *vma;
+	vm_fault_t ret;
+
+	address = untagged_addr_remote(mm, address);
+
+	if (unlocked)
+		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+
+retry:
+	vma = gup_vma_lookup(mm, address);
+	if (!vma)
+		return -EFAULT;
+
+	if (!vma_permits_fault(vma, fault_flags))
+		return -EFAULT;
+
+	if ((fault_flags & FAULT_FLAG_KILLABLE) &&
+	    fatal_signal_pending(current))
+		return -EINTR;
+
+	ret = handle_mm_fault(vma, address, fault_flags, NULL);
+
+	if (ret & VM_FAULT_COMPLETED) {
+		/*
+		 * NOTE: it's a pity that we need to retake the lock here
+		 * to pair with the unlock() in the callers. Ideally we
+		 * could tell the callers so they do not need to unlock.
+		 */
+		mmap_read_lock(mm);
+		*unlocked = true;
+		return 0;
+	}
+
+	if (ret & VM_FAULT_ERROR) {
+		int err = vm_fault_to_errno(ret, 0);
+
+		if (err)
+			return err;
+		BUG();
+	}
+
+	if (ret & VM_FAULT_RETRY) {
+		mmap_read_lock(mm);
+		*unlocked = true;
+		fault_flags |= FAULT_FLAG_TRIED;
+		goto retry;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fixup_user_fault);
+
+/*
+ * GUP always responds to fatal signals.  When FOLL_INTERRUPTIBLE is
+ * specified, it'll also respond to generic signals.  The caller of GUP
+ * that has FOLL_INTERRUPTIBLE should take care of the GUP interruption.
+ */
+static bool gup_signal_pending(unsigned int flags)
+{
+	if (fatal_signal_pending(current))
+		return true;
+
+	if (!(flags & FOLL_INTERRUPTIBLE))
+		return false;
+
+	return signal_pending(current);
+}
+
+/*
+ * Locking: (*locked == 1) means that the mmap_lock has already been acquired by
+ * the caller. This function may drop the mmap_lock. If it does so, then it will
+ * set (*locked = 0).
+ *
+ * (*locked == 0) means that the caller expects this function to acquire and
+ * drop the mmap_lock. Therefore, the value of *locked will still be zero when
+ * the function returns, even though it may have changed temporarily during
+ * function execution.
+ *
+ * Please note that this function, unlike __get_user_pages(), will not return 0
+ * for nr_pages > 0, unless FOLL_NOWAIT is used.
+ */
+static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
+						unsigned long start,
+						unsigned long nr_pages,
+						struct page **pages,
+						int *locked,
+						unsigned int flags)
+{
+	long ret, pages_done;
+	bool must_unlock = false;
+
+	/*
+	 * The internal caller expects GUP to manage the lock internally and the
+	 * lock must be released when this returns.
+	 */
+	if (!*locked) {
+		if (mmap_read_lock_killable(mm))
+			return -EAGAIN;
+		must_unlock = true;
+		*locked = 1;
+	}
+	else
+		mmap_assert_locked(mm);
+
+	if (flags & FOLL_PIN)
+		mm_set_has_pinned_flag(&mm->flags);
+
+	/*
+	 * FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior
+	 * is to set FOLL_GET if the caller wants pages[] filled in (but has
+	 * carelessly failed to specify FOLL_GET), so keep doing that, but only
+	 * for FOLL_GET, not for the newer FOLL_PIN.
+	 *
+	 * FOLL_PIN always expects pages to be non-null, but no need to assert
+	 * that here, as any failures will be obvious enough.
+	 */
+	if (pages && !(flags & FOLL_PIN))
+		flags |= FOLL_GET;
+
+	pages_done = 0;
+	for (;;) {
+		ret = __get_user_pages(mm, start, nr_pages, flags, pages,
+				       locked);
+		if (!(flags & FOLL_UNLOCKABLE)) {
+			/* VM_FAULT_RETRY couldn't trigger, bypass */
+			pages_done = ret;
+			break;
+		}
+
+		/* VM_FAULT_RETRY or VM_FAULT_COMPLETED cannot return errors */
+		if (!*locked) {
+			BUG_ON(ret < 0);
+			BUG_ON(ret >= nr_pages);
+		}
+
+		if (ret > 0) {
+			nr_pages -= ret;
+			pages_done += ret;
+			if (!nr_pages)
+				break;
+		}
+		if (*locked) {
+			/*
+			 * VM_FAULT_RETRY didn't trigger or it was a
+			 * FOLL_NOWAIT.
+			 */
+			if (!pages_done)
+				pages_done = ret;
+			break;
+		}
+		/*
+		 * VM_FAULT_RETRY triggered, so seek to the faulting offset.
+		 * For the prefault case (!pages) we only update counts.
+		 */
+		if (likely(pages))
+			pages += ret;
+		start += ret << PAGE_SHIFT;
+
+		/* The lock was temporarily dropped, so we must unlock later */
+		must_unlock = true;
+
+retry:
+		/*
+		 * Repeat on the address that fired VM_FAULT_RETRY
+		 * with both FAULT_FLAG_ALLOW_RETRY and
+		 * FAULT_FLAG_TRIED.  Note that GUP can be interrupted
+		 * by fatal signals of even common signals, depending on
+		 * the caller's request. So we need to check it before we
+		 * start trying again otherwise it can loop forever.
+		 */
+		if (gup_signal_pending(flags)) {
+			if (!pages_done)
+				pages_done = -EINTR;
+			break;
+		}
+
+		ret = mmap_read_lock_killable(mm);
+		if (ret) {
+			BUG_ON(ret > 0);
+			if (!pages_done)
+				pages_done = ret;
+			break;
+		}
+
+		*locked = 1;
+		ret = __get_user_pages(mm, start, 1, flags | FOLL_TRIED,
+				       pages, locked);
+		if (!*locked) {
+			/* Continue to retry until we succeeded */
+			BUG_ON(ret != 0);
+			goto retry;
+		}
+		if (ret != 1) {
+			BUG_ON(ret > 1);
+			if (!pages_done)
+				pages_done = ret;
+			break;
+		}
+		nr_pages--;
+		pages_done++;
+		if (!nr_pages)
+			break;
+		if (likely(pages))
+			pages++;
+		start += PAGE_SIZE;
+	}
+	if (must_unlock && *locked) {
+		/*
+		 * We either temporarily dropped the lock, or the caller
+		 * requested that we both acquire and drop the lock. Either way,
+		 * we must now unlock, and notify the caller of that state.
+		 */
+		mmap_read_unlock(mm);
+		*locked = 0;
+	}
+	return pages_done;
+}
+
+/**
+ * populate_vma_page_range() -  populate a range of pages in the vma.
+ * @vma:   target vma
+ * @start: start address
+ * @end:   end address
+ * @locked: whether the mmap_lock is still held
+ *
+ * This takes care of mlocking the pages too if VM_LOCKED is set.
+ *
+ * Return either number of pages pinned in the vma, or a negative error
+ * code on error.
+ *
+ * vma->vm_mm->mmap_lock must be held.
+ *
+ * If @locked is NULL, it may be held for read or write and will
+ * be unperturbed.
+ *
+ * If @locked is non-NULL, it must held for read only and may be
+ * released.  If it's released, *@locked will be set to 0.
+ */
+long populate_vma_page_range(struct vm_area_struct *vma,
+		unsigned long start, unsigned long end, int *locked)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long nr_pages = (end - start) / PAGE_SIZE;
+	int local_locked = 1;
+	int gup_flags;
+	long ret;
+
+	VM_BUG_ON(!PAGE_ALIGNED(start));
+	VM_BUG_ON(!PAGE_ALIGNED(end));
+	VM_BUG_ON_VMA(start < vma->vm_start, vma);
+	VM_BUG_ON_VMA(end   > vma->vm_end, vma);
+	mmap_assert_locked(mm);
+
+	/*
+	 * Rightly or wrongly, the VM_LOCKONFAULT case has never used
+	 * faultin_page() to break COW, so it has no work to do here.
+	 */
+	if (vma->vm_flags & VM_LOCKONFAULT)
+		return nr_pages;
+
+	gup_flags = FOLL_TOUCH;
+	/*
+	 * We want to touch writable mappings with a write fault in order
+	 * to break COW, except for shared mappings because these don't COW
+	 * and we would not want to dirty them for nothing.
+	 */
+	if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
+		gup_flags |= FOLL_WRITE;
+
+	/*
+	 * We want mlock to succeed for regions that have any permissions
+	 * other than PROT_NONE.
+	 */
+	if (vma_is_accessible(vma))
+		gup_flags |= FOLL_FORCE;
+
+	if (locked)
+		gup_flags |= FOLL_UNLOCKABLE;
+
+	/*
+	 * We made sure addr is within a VMA, so the following will
+	 * not result in a stack expansion that recurses back here.
+	 */
+	ret = __get_user_pages(mm, start, nr_pages, gup_flags,
+			       NULL, locked ? locked : &local_locked);
+	lru_add_drain();
+	return ret;
+}
+
+/*
+ * faultin_vma_page_range() - populate (prefault) page tables inside the
+ *			      given VMA range readable/writable
+ *
+ * This takes care of mlocking the pages, too, if VM_LOCKED is set.
+ *
+ * @vma: target vma
+ * @start: start address
+ * @end: end address
+ * @write: whether to prefault readable or writable
+ * @locked: whether the mmap_lock is still held
+ *
+ * Returns either number of processed pages in the vma, or a negative error
+ * code on error (see __get_user_pages()).
+ *
+ * vma->vm_mm->mmap_lock must be held. The range must be page-aligned and
+ * covered by the VMA. If it's released, *@locked will be set to 0.
+ */
+long faultin_vma_page_range(struct vm_area_struct *vma, unsigned long start,
+			    unsigned long end, bool write, int *locked)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long nr_pages = (end - start) / PAGE_SIZE;
+	int gup_flags;
+	long ret;
+
+	VM_BUG_ON(!PAGE_ALIGNED(start));
+	VM_BUG_ON(!PAGE_ALIGNED(end));
+	VM_BUG_ON_VMA(start < vma->vm_start, vma);
+	VM_BUG_ON_VMA(end > vma->vm_end, vma);
+	mmap_assert_locked(mm);
+
+	/*
+	 * FOLL_TOUCH: Mark page accessed and thereby young; will also mark
+	 *	       the page dirty with FOLL_WRITE -- which doesn't make a
+	 *	       difference with !FOLL_FORCE, because the page is writable
+	 *	       in the page table.
+	 * FOLL_HWPOISON: Return -EHWPOISON instead of -EFAULT when we hit
+	 *		  a poisoned page.
+	 * !FOLL_FORCE: Require proper access permissions.
+	 */
+	gup_flags = FOLL_TOUCH | FOLL_HWPOISON | FOLL_UNLOCKABLE;
+	if (write)
+		gup_flags |= FOLL_WRITE;
+
+	/*
+	 * We want to report -EINVAL instead of -EFAULT for any permission
+	 * problems or incompatible mappings.
+	 */
+	if (check_vma_flags(vma, gup_flags))
+		return -EINVAL;
+
+	ret = __get_user_pages(mm, start, nr_pages, gup_flags,
+			       NULL, locked);
+	lru_add_drain();
+	return ret;
+}
+
+/*
+ * __mm_populate - populate and/or mlock pages within a range of address space.
+ *
+ * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
+ * flags. VMAs must be already marked with the desired vm_flags, and
+ * mmap_lock must not be held.
+ */
+int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
+{
+	struct mm_struct *mm = current->mm;
+	unsigned long end, nstart, nend;
+	struct vm_area_struct *vma = NULL;
+	int locked = 0;
+	long ret = 0;
+
+	end = start + len;
+
+	for (nstart = start; nstart < end; nstart = nend) {
+		/*
+		 * We want to fault in pages for [nstart; end) address range.
+		 * Find first corresponding VMA.
+		 */
+		if (!locked) {
+			locked = 1;
+			mmap_read_lock(mm);
+			vma = find_vma_intersection(mm, nstart, end);
+		} else if (nstart >= vma->vm_end)
+			vma = find_vma_intersection(mm, vma->vm_end, end);
+
+		if (!vma)
+			break;
+		/*
+		 * Set [nstart; nend) to intersection of desired address
+		 * range with the first VMA. Also, skip undesirable VMA types.
+		 */
+		nend = min(end, vma->vm_end);
+		if (vma->vm_flags & (VM_IO | VM_PFNMAP))
+			continue;
+		if (nstart < vma->vm_start)
+			nstart = vma->vm_start;
+		/*
+		 * Now fault in a range of pages. populate_vma_page_range()
+		 * double checks the vma flags, so that it won't mlock pages
+		 * if the vma was already munlocked.
+		 */
+		ret = populate_vma_page_range(vma, nstart, nend, &locked);
+		if (ret < 0) {
+			if (ignore_errors) {
+				ret = 0;
+				continue;	/* continue at next VMA */
+			}
+			break;
+		}
+		nend = nstart + ret * PAGE_SIZE;
+		ret = 0;
+	}
+	if (locked)
+		mmap_read_unlock(mm);
+	return ret;	/* 0 or negative error code */
+}
+#else /* CONFIG_MMU */
+static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
+		unsigned long nr_pages, struct page **pages,
+		int *locked, unsigned int foll_flags)
+{
+	struct vm_area_struct *vma;
+	bool must_unlock = false;
+	unsigned long vm_flags;
+	long i;
+
+	if (!nr_pages)
+		return 0;
+
+	/*
+	 * The internal caller expects GUP to manage the lock internally and the
+	 * lock must be released when this returns.
+	 */
+	if (!*locked) {
+		if (mmap_read_lock_killable(mm))
+			return -EAGAIN;
+		must_unlock = true;
+		*locked = 1;
+	}
+
+	/* calculate required read or write permissions.
+	 * If FOLL_FORCE is set, we only require the "MAY" flags.
+	 */
+	vm_flags  = (foll_flags & FOLL_WRITE) ?
+			(VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
+	vm_flags &= (foll_flags & FOLL_FORCE) ?
+			(VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
+
+	for (i = 0; i < nr_pages; i++) {
+		vma = find_vma(mm, start);
+		if (!vma)
+			break;
+
+		/* protect what we can, including chardevs */
+		if ((vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
+		    !(vm_flags & vma->vm_flags))
+			break;
+
+		if (pages) {
+			pages[i] = virt_to_page((void *)start);
+			if (pages[i])
+				get_page(pages[i]);
+		}
+
+		start = (start + PAGE_SIZE) & PAGE_MASK;
+	}
+
+	if (must_unlock && *locked) {
+		mmap_read_unlock(mm);
+		*locked = 0;
+	}
+
+	return i ? : -EFAULT;
+}
+#endif /* !CONFIG_MMU */
+
+/**
+ * fault_in_writeable - fault in userspace address range for writing
+ * @uaddr: start of address range
+ * @size: size of address range
+ *
+ * Returns the number of bytes not faulted in (like copy_to_user() and
+ * copy_from_user()).
+ */
+size_t fault_in_writeable(char __user *uaddr, size_t size)
+{
+	char __user *start = uaddr, *end;
+
+	if (unlikely(size == 0))
+		return 0;
+	if (!user_write_access_begin(uaddr, size))
+		return size;
+	if (!PAGE_ALIGNED(uaddr)) {
+		unsafe_put_user(0, uaddr, out);
+		uaddr = (char __user *)PAGE_ALIGN((unsigned long)uaddr);
+	}
+	end = (char __user *)PAGE_ALIGN((unsigned long)start + size);
+	if (unlikely(end < start))
+		end = NULL;
+	while (uaddr != end) {
+		unsafe_put_user(0, uaddr, out);
+		uaddr += PAGE_SIZE;
+	}
+
+out:
+	user_write_access_end();
+	if (size > uaddr - start)
+		return size - (uaddr - start);
+	return 0;
+}
+EXPORT_SYMBOL(fault_in_writeable);
+
+/**
+ * fault_in_subpage_writeable - fault in an address range for writing
+ * @uaddr: start of address range
+ * @size: size of address range
+ *
+ * Fault in a user address range for writing while checking for permissions at
+ * sub-page granularity (e.g. arm64 MTE). This function should be used when
+ * the caller cannot guarantee forward progress of a copy_to_user() loop.
+ *
+ * Returns the number of bytes not faulted in (like copy_to_user() and
+ * copy_from_user()).
+ */
+size_t fault_in_subpage_writeable(char __user *uaddr, size_t size)
+{
+	size_t faulted_in;
+
+	/*
+	 * Attempt faulting in at page granularity first for page table
+	 * permission checking. The arch-specific probe_subpage_writeable()
+	 * functions may not check for this.
+	 */
+	faulted_in = size - fault_in_writeable(uaddr, size);
+	if (faulted_in)
+		faulted_in -= probe_subpage_writeable(uaddr, faulted_in);
+
+	return size - faulted_in;
+}
+EXPORT_SYMBOL(fault_in_subpage_writeable);
+
+/*
+ * fault_in_safe_writeable - fault in an address range for writing
+ * @uaddr: start of address range
+ * @size: length of address range
+ *
+ * Faults in an address range for writing.  This is primarily useful when we
+ * already know that some or all of the pages in the address range aren't in
+ * memory.
+ *
+ * Unlike fault_in_writeable(), this function is non-destructive.
+ *
+ * Note that we don't pin or otherwise hold the pages referenced that we fault
+ * in.  There's no guarantee that they'll stay in memory for any duration of
+ * time.
+ *
+ * Returns the number of bytes not faulted in, like copy_to_user() and
+ * copy_from_user().
+ */
+size_t fault_in_safe_writeable(const char __user *uaddr, size_t size)
+{
+	unsigned long start = (unsigned long)uaddr, end;
+	struct mm_struct *mm = current->mm;
+	bool unlocked = false;
+
+	if (unlikely(size == 0))
+		return 0;
+	end = PAGE_ALIGN(start + size);
+	if (end < start)
+		end = 0;
+
+	mmap_read_lock(mm);
+	do {
+		if (fixup_user_fault(mm, start, FAULT_FLAG_WRITE, &unlocked))
+			break;
+		start = (start + PAGE_SIZE) & PAGE_MASK;
+	} while (start != end);
+	mmap_read_unlock(mm);
+
+	if (size > (unsigned long)uaddr - start)
+		return size - ((unsigned long)uaddr - start);
+	return 0;
+}
+EXPORT_SYMBOL(fault_in_safe_writeable);
+
+/**
+ * fault_in_readable - fault in userspace address range for reading
+ * @uaddr: start of user address range
+ * @size: size of user address range
+ *
+ * Returns the number of bytes not faulted in (like copy_to_user() and
+ * copy_from_user()).
+ */
+size_t fault_in_readable(const char __user *uaddr, size_t size)
+{
+	const char __user *start = uaddr, *end;
+	volatile char c;
+
+	if (unlikely(size == 0))
+		return 0;
+	if (!user_read_access_begin(uaddr, size))
+		return size;
+	if (!PAGE_ALIGNED(uaddr)) {
+		unsafe_get_user(c, uaddr, out);
+		uaddr = (const char __user *)PAGE_ALIGN((unsigned long)uaddr);
+	}
+	end = (const char __user *)PAGE_ALIGN((unsigned long)start + size);
+	if (unlikely(end < start))
+		end = NULL;
+	while (uaddr != end) {
+		unsafe_get_user(c, uaddr, out);
+		uaddr += PAGE_SIZE;
+	}
+
+out:
+	user_read_access_end();
+	(void)c;
+	if (size > uaddr - start)
+		return size - (uaddr - start);
+	return 0;
+}
+EXPORT_SYMBOL(fault_in_readable);
+
+/**
+ * get_dump_page() - pin user page in memory while writing it to core dump
+ * @addr: user address
+ *
+ * Returns struct page pointer of user page pinned for dump,
+ * to be freed afterwards by put_page().
+ *
+ * Returns NULL on any kind of failure - a hole must then be inserted into
+ * the corefile, to preserve alignment with its headers; and also returns
+ * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
+ * allowing a hole to be left in the corefile to save disk space.
+ *
+ * Called without mmap_lock (takes and releases the mmap_lock by itself).
+ */
+#ifdef CONFIG_ELF_CORE
+struct page *get_dump_page(unsigned long addr)
+{
+	struct page *page;
+	int locked = 0;
+	int ret;
+
+	ret = __get_user_pages_locked(current->mm, addr, 1, &page, &locked,
+				      FOLL_FORCE | FOLL_DUMP | FOLL_GET);
+	return (ret == 1) ? page : NULL;
+}
+#endif /* CONFIG_ELF_CORE */
+
+#ifdef CONFIG_MIGRATION
+/*
+ * Returns the number of collected pages. Return value is always >= 0.
+ */
+static unsigned long collect_longterm_unpinnable_pages(
+					struct list_head *movable_page_list,
+					unsigned long nr_pages,
+					struct page **pages)
+{
+	unsigned long i, collected = 0;
+	struct folio *prev_folio = NULL;
+	bool drain_allow = true;
+
+	for (i = 0; i < nr_pages; i++) {
+		struct folio *folio = page_folio(pages[i]);
+
+		if (folio == prev_folio)
+			continue;
+		prev_folio = folio;
+
+		if (folio_is_longterm_pinnable(folio))
+			continue;
+
+		collected++;
+
+		if (folio_is_device_coherent(folio))
+			continue;
+
+		if (folio_test_hugetlb(folio)) {
+			isolate_hugetlb(folio, movable_page_list);
+			continue;
+		}
+
+		if (!folio_test_lru(folio) && drain_allow) {
+			lru_add_drain_all();
+			drain_allow = false;
+		}
+
+		if (!folio_isolate_lru(folio))
+			continue;
+
+		list_add_tail(&folio->lru, movable_page_list);
+		node_stat_mod_folio(folio,
+				    NR_ISOLATED_ANON + folio_is_file_lru(folio),
+				    folio_nr_pages(folio));
+	}
+
+	return collected;
+}
+
+/*
+ * Unpins all pages and migrates device coherent pages and movable_page_list.
+ * Returns -EAGAIN if all pages were successfully migrated or -errno for failure
+ * (or partial success).
+ */
+static int migrate_longterm_unpinnable_pages(
+					struct list_head *movable_page_list,
+					unsigned long nr_pages,
+					struct page **pages)
+{
+	int ret;
+	unsigned long i;
+
+	for (i = 0; i < nr_pages; i++) {
+		struct folio *folio = page_folio(pages[i]);
+
+		if (folio_is_device_coherent(folio)) {
+			/*
+			 * Migration will fail if the page is pinned, so convert
+			 * the pin on the source page to a normal reference.
+			 */
+			pages[i] = NULL;
+			folio_get(folio);
+			gup_put_folio(folio, 1, FOLL_PIN);
+
+			if (migrate_device_coherent_page(&folio->page)) {
+				ret = -EBUSY;
+				goto err;
+			}
+
+			continue;
+		}
+
+		/*
+		 * We can't migrate pages with unexpected references, so drop
+		 * the reference obtained by __get_user_pages_locked().
+		 * Migrating pages have been added to movable_page_list after
+		 * calling folio_isolate_lru() which takes a reference so the
+		 * page won't be freed if it's migrating.
+		 */
+		unpin_user_page(pages[i]);
+		pages[i] = NULL;
+	}
+
+	if (!list_empty(movable_page_list)) {
+		struct migration_target_control mtc = {
+			.nid = NUMA_NO_NODE,
+			.gfp_mask = GFP_USER | __GFP_NOWARN,
+		};
+
+		if (migrate_pages(movable_page_list, alloc_migration_target,
+				  NULL, (unsigned long)&mtc, MIGRATE_SYNC,
+				  MR_LONGTERM_PIN, NULL)) {
+			ret = -ENOMEM;
+			goto err;
+		}
+	}
+
+	putback_movable_pages(movable_page_list);
+
+	return -EAGAIN;
+
+err:
+	for (i = 0; i < nr_pages; i++)
+		if (pages[i])
+			unpin_user_page(pages[i]);
+	putback_movable_pages(movable_page_list);
+
+	return ret;
+}
+
+/*
+ * Check whether all pages are *allowed* to be pinned. Rather confusingly, all
+ * pages in the range are required to be pinned via FOLL_PIN, before calling
+ * this routine.
+ *
+ * If any pages in the range are not allowed to be pinned, then this routine
+ * will migrate those pages away, unpin all the pages in the range and return
+ * -EAGAIN. The caller should re-pin the entire range with FOLL_PIN and then
+ * call this routine again.
+ *
+ * If an error other than -EAGAIN occurs, this indicates a migration failure.
+ * The caller should give up, and propagate the error back up the call stack.
+ *
+ * If everything is OK and all pages in the range are allowed to be pinned, then
+ * this routine leaves all pages pinned and returns zero for success.
+ */
+static long check_and_migrate_movable_pages(unsigned long nr_pages,
+					    struct page **pages)
+{
+	unsigned long collected;
+	LIST_HEAD(movable_page_list);
+
+	collected = collect_longterm_unpinnable_pages(&movable_page_list,
+						nr_pages, pages);
+	if (!collected)
+		return 0;
+
+	return migrate_longterm_unpinnable_pages(&movable_page_list, nr_pages,
+						pages);
+}
+#else
+static long check_and_migrate_movable_pages(unsigned long nr_pages,
+					    struct page **pages)
+{
+	return 0;
+}
+#endif /* CONFIG_MIGRATION */
+
+/*
+ * __gup_longterm_locked() is a wrapper for __get_user_pages_locked which
+ * allows us to process the FOLL_LONGTERM flag.
+ */
+static long __gup_longterm_locked(struct mm_struct *mm,
+				  unsigned long start,
+				  unsigned long nr_pages,
+				  struct page **pages,
+				  int *locked,
+				  unsigned int gup_flags)
+{
+	unsigned int flags;
+	long rc, nr_pinned_pages;
+
+	if (!(gup_flags & FOLL_LONGTERM))
+		return __get_user_pages_locked(mm, start, nr_pages, pages,
+					       locked, gup_flags);
+
+	flags = memalloc_pin_save();
+	do {
+		nr_pinned_pages = __get_user_pages_locked(mm, start, nr_pages,
+							  pages, locked,
+							  gup_flags);
+		if (nr_pinned_pages <= 0) {
+			rc = nr_pinned_pages;
+			break;
+		}
+
+		/* FOLL_LONGTERM implies FOLL_PIN */
+		rc = check_and_migrate_movable_pages(nr_pinned_pages, pages);
+	} while (rc == -EAGAIN);
+	memalloc_pin_restore(flags);
+	return rc ? rc : nr_pinned_pages;
+}
+
+/*
+ * Check that the given flags are valid for the exported gup/pup interface, and
+ * update them with the required flags that the caller must have set.
+ */
+static bool is_valid_gup_args(struct page **pages, int *locked,
+			      unsigned int *gup_flags_p, unsigned int to_set)
+{
+	unsigned int gup_flags = *gup_flags_p;
+
+	/*
+	 * These flags not allowed to be specified externally to the gup
+	 * interfaces:
+	 * - FOLL_PIN/FOLL_TRIED/FOLL_FAST_ONLY are internal only
+	 * - FOLL_REMOTE is internal only and used on follow_page()
+	 * - FOLL_UNLOCKABLE is internal only and used if locked is !NULL
+	 */
+	if (WARN_ON_ONCE(gup_flags & (FOLL_PIN | FOLL_TRIED | FOLL_UNLOCKABLE |
+				      FOLL_REMOTE | FOLL_FAST_ONLY)))
+		return false;
+
+	gup_flags |= to_set;
+	if (locked) {
+		/* At the external interface locked must be set */
+		if (WARN_ON_ONCE(*locked != 1))
+			return false;
+
+		gup_flags |= FOLL_UNLOCKABLE;
+	}
+
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
+			 (FOLL_PIN | FOLL_GET)))
+		return false;
+
+	/* LONGTERM can only be specified when pinning */
+	if (WARN_ON_ONCE(!(gup_flags & FOLL_PIN) && (gup_flags & FOLL_LONGTERM)))
+		return false;
+
+	/* Pages input must be given if using GET/PIN */
+	if (WARN_ON_ONCE((gup_flags & (FOLL_GET | FOLL_PIN)) && !pages))
+		return false;
+
+	/* We want to allow the pgmap to be hot-unplugged at all times */
+	if (WARN_ON_ONCE((gup_flags & FOLL_LONGTERM) &&
+			 (gup_flags & FOLL_PCI_P2PDMA)))
+		return false;
+
+	*gup_flags_p = gup_flags;
+	return true;
+}
+
+#ifdef CONFIG_MMU
+/**
+ * get_user_pages_remote() - pin user pages in memory
+ * @mm:		mm_struct of target mm
+ * @start:	starting user address
+ * @nr_pages:	number of pages from start to pin
+ * @gup_flags:	flags modifying lookup behaviour
+ * @pages:	array that receives pointers to the pages pinned.
+ *		Should be at least nr_pages long. Or NULL, if caller
+ *		only intends to ensure the pages are faulted in.
+ * @locked:	pointer to lock flag indicating whether lock is held and
+ *		subsequently whether VM_FAULT_RETRY functionality can be
+ *		utilised. Lock must initially be held.
+ *
+ * Returns either number of pages pinned (which may be less than the
+ * number requested), or an error. Details about the return value:
+ *
+ * -- If nr_pages is 0, returns 0.
+ * -- If nr_pages is >0, but no pages were pinned, returns -errno.
+ * -- If nr_pages is >0, and some pages were pinned, returns the number of
+ *    pages pinned. Again, this may be less than nr_pages.
+ *
+ * The caller is responsible for releasing returned @pages, via put_page().
+ *
+ * Must be called with mmap_lock held for read or write.
+ *
+ * get_user_pages_remote walks a process's page tables and takes a reference
+ * to each struct page that each user address corresponds to at a given
+ * instant. That is, it takes the page that would be accessed if a user
+ * thread accesses the given user virtual address at that instant.
+ *
+ * This does not guarantee that the page exists in the user mappings when
+ * get_user_pages_remote returns, and there may even be a completely different
+ * page there in some cases (eg. if mmapped pagecache has been invalidated
+ * and subsequently re-faulted). However it does guarantee that the page
+ * won't be freed completely. And mostly callers simply care that the page
+ * contains data that was valid *at some point in time*. Typically, an IO
+ * or similar operation cannot guarantee anything stronger anyway because
+ * locks can't be held over the syscall boundary.
+ *
+ * If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the page
+ * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must
+ * be called after the page is finished with, and before put_page is called.
+ *
+ * get_user_pages_remote is typically used for fewer-copy IO operations,
+ * to get a handle on the memory by some means other than accesses
+ * via the user virtual addresses. The pages may be submitted for
+ * DMA to devices or accessed via their kernel linear mapping (via the
+ * kmap APIs). Care should be taken to use the correct cache flushing APIs.
+ *
+ * See also get_user_pages_fast, for performance critical applications.
+ *
+ * get_user_pages_remote should be phased out in favor of
+ * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
+ * should use get_user_pages_remote because it cannot pass
+ * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
+ */
+long get_user_pages_remote(struct mm_struct *mm,
+		unsigned long start, unsigned long nr_pages,
+		unsigned int gup_flags, struct page **pages,
+		int *locked)
+{
+	int local_locked = 1;
+
+	if (!is_valid_gup_args(pages, locked, &gup_flags,
+			       FOLL_TOUCH | FOLL_REMOTE))
+		return -EINVAL;
+
+	return __get_user_pages_locked(mm, start, nr_pages, pages,
+				       locked ? locked : &local_locked,
+				       gup_flags);
+}
+EXPORT_SYMBOL(get_user_pages_remote);
+
+#else /* CONFIG_MMU */
+long get_user_pages_remote(struct mm_struct *mm,
+			   unsigned long start, unsigned long nr_pages,
+			   unsigned int gup_flags, struct page **pages,
+			   int *locked)
+{
+	return 0;
+}
+#endif /* !CONFIG_MMU */
+
+/**
+ * get_user_pages() - pin user pages in memory
+ * @start:      starting user address
+ * @nr_pages:   number of pages from start to pin
+ * @gup_flags:  flags modifying lookup behaviour
+ * @pages:      array that receives pointers to the pages pinned.
+ *              Should be at least nr_pages long. Or NULL, if caller
+ *              only intends to ensure the pages are faulted in.
+ *
+ * This is the same as get_user_pages_remote(), just with a less-flexible
+ * calling convention where we assume that the mm being operated on belongs to
+ * the current task, and doesn't allow passing of a locked parameter.  We also
+ * obviously don't pass FOLL_REMOTE in here.
+ */
+long get_user_pages(unsigned long start, unsigned long nr_pages,
+		    unsigned int gup_flags, struct page **pages)
+{
+	int locked = 1;
+
+	if (!is_valid_gup_args(pages, NULL, &gup_flags, FOLL_TOUCH))
+		return -EINVAL;
+
+	return __get_user_pages_locked(current->mm, start, nr_pages, pages,
+				       &locked, gup_flags);
+}
+EXPORT_SYMBOL(get_user_pages);
+
+/*
+ * get_user_pages_unlocked() is suitable to replace the form:
+ *
+ *      mmap_read_lock(mm);
+ *      get_user_pages(mm, ..., pages, NULL);
+ *      mmap_read_unlock(mm);
+ *
+ *  with:
+ *
+ *      get_user_pages_unlocked(mm, ..., pages);
+ *
+ * It is functionally equivalent to get_user_pages_fast so
+ * get_user_pages_fast should be used instead if specific gup_flags
+ * (e.g. FOLL_FORCE) are not required.
+ */
+long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
+			     struct page **pages, unsigned int gup_flags)
+{
+	int locked = 0;
+
+	if (!is_valid_gup_args(pages, NULL, &gup_flags,
+			       FOLL_TOUCH | FOLL_UNLOCKABLE))
+		return -EINVAL;
+
+	return __get_user_pages_locked(current->mm, start, nr_pages, pages,
+				       &locked, gup_flags);
+}
+EXPORT_SYMBOL(get_user_pages_unlocked);
+
+/*
+ * Fast GUP
+ *
+ * get_user_pages_fast attempts to pin user pages by walking the page
+ * tables directly and avoids taking locks. Thus the walker needs to be
+ * protected from page table pages being freed from under it, and should
+ * block any THP splits.
+ *
+ * One way to achieve this is to have the walker disable interrupts, and
+ * rely on IPIs from the TLB flushing code blocking before the page table
+ * pages are freed. This is unsuitable for architectures that do not need
+ * to broadcast an IPI when invalidating TLBs.
+ *
+ * Another way to achieve this is to batch up page table containing pages
+ * belonging to more than one mm_user, then rcu_sched a callback to free those
+ * pages. Disabling interrupts will allow the fast_gup walker to both block
+ * the rcu_sched callback, and an IPI that we broadcast for splitting THPs
+ * (which is a relatively rare event). The code below adopts this strategy.
+ *
+ * Before activating this code, please be aware that the following assumptions
+ * are currently made:
+ *
+ *  *) Either MMU_GATHER_RCU_TABLE_FREE is enabled, and tlb_remove_table() is used to
+ *  free pages containing page tables or TLB flushing requires IPI broadcast.
+ *
+ *  *) ptes can be read atomically by the architecture.
+ *
+ *  *) access_ok is sufficient to validate userspace address ranges.
+ *
+ * The last two assumptions can be relaxed by the addition of helper functions.
+ *
+ * This code is based heavily on the PowerPC implementation by Nick Piggin.
+ */
+#ifdef CONFIG_HAVE_FAST_GUP
+
+/*
+ * Used in the GUP-fast path to determine whether a pin is permitted for a
+ * specific folio.
+ *
+ * This call assumes the caller has pinned the folio, that the lowest page table
+ * level still points to this folio, and that interrupts have been disabled.
+ *
+ * Writing to pinned file-backed dirty tracked folios is inherently problematic
+ * (see comment describing the writable_file_mapping_allowed() function). We
+ * therefore try to avoid the most egregious case of a long-term mapping doing
+ * so.
+ *
+ * This function cannot be as thorough as that one as the VMA is not available
+ * in the fast path, so instead we whitelist known good cases and if in doubt,
+ * fall back to the slow path.
+ */
+static bool folio_fast_pin_allowed(struct folio *folio, unsigned int flags)
+{
+	struct address_space *mapping;
+	unsigned long mapping_flags;
+
+	/*
+	 * If we aren't pinning then no problematic write can occur. A long term
+	 * pin is the most egregious case so this is the one we disallow.
+	 */
+	if ((flags & (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) !=
+	    (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE))
+		return true;
+
+	/* The folio is pinned, so we can safely access folio fields. */
+
+	if (WARN_ON_ONCE(folio_test_slab(folio)))
+		return false;
+
+	/* hugetlb mappings do not require dirty-tracking. */
+	if (folio_test_hugetlb(folio))
+		return true;
+
+	/*
+	 * GUP-fast disables IRQs. When IRQS are disabled, RCU grace periods
+	 * cannot proceed, which means no actions performed under RCU can
+	 * proceed either.
+	 *
+	 * inodes and thus their mappings are freed under RCU, which means the
+	 * mapping cannot be freed beneath us and thus we can safely dereference
+	 * it.
+	 */
+	lockdep_assert_irqs_disabled();
+
+	/*
+	 * However, there may be operations which _alter_ the mapping, so ensure
+	 * we read it once and only once.
+	 */
+	mapping = READ_ONCE(folio->mapping);
+
+	/*
+	 * The mapping may have been truncated, in any case we cannot determine
+	 * if this mapping is safe - fall back to slow path to determine how to
+	 * proceed.
+	 */
+	if (!mapping)
+		return false;
+
+	/* Anonymous folios pose no problem. */
+	mapping_flags = (unsigned long)mapping & PAGE_MAPPING_FLAGS;
+	if (mapping_flags)
+		return mapping_flags & PAGE_MAPPING_ANON;
+
+	/*
+	 * At this point, we know the mapping is non-null and points to an
+	 * address_space object. The only remaining whitelisted file system is
+	 * shmem.
+	 */
+	return shmem_mapping(mapping);
+}
+
+static void __maybe_unused undo_dev_pagemap(int *nr, int nr_start,
+					    unsigned int flags,
+					    struct page **pages)
+{
+	while ((*nr) - nr_start) {
+		struct page *page = pages[--(*nr)];
+
+		ClearPageReferenced(page);
+		if (flags & FOLL_PIN)
+			unpin_user_page(page);
+		else
+			put_page(page);
+	}
+}
+
+#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
+/*
+ * Fast-gup relies on pte change detection to avoid concurrent pgtable
+ * operations.
+ *
+ * To pin the page, fast-gup needs to do below in order:
+ * (1) pin the page (by prefetching pte), then (2) check pte not changed.
+ *
+ * For the rest of pgtable operations where pgtable updates can be racy
+ * with fast-gup, we need to do (1) clear pte, then (2) check whether page
+ * is pinned.
+ *
+ * Above will work for all pte-level operations, including THP split.
+ *
+ * For THP collapse, it's a bit more complicated because fast-gup may be
+ * walking a pgtable page that is being freed (pte is still valid but pmd
+ * can be cleared already).  To avoid race in such condition, we need to
+ * also check pmd here to make sure pmd doesn't change (corresponds to
+ * pmdp_collapse_flush() in the THP collapse code path).
+ */
+static int gup_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
+			 unsigned long end, unsigned int flags,
+			 struct page **pages, int *nr)
+{
+	struct dev_pagemap *pgmap = NULL;
+	int nr_start = *nr, ret = 0;
+	pte_t *ptep, *ptem;
+
+	ptem = ptep = pte_offset_map(&pmd, addr);
+	if (!ptep)
+		return 0;
+	do {
+		pte_t pte = ptep_get_lockless(ptep);
+		struct page *page;
+		struct folio *folio;
+
+		/*
+		 * Always fallback to ordinary GUP on PROT_NONE-mapped pages:
+		 * pte_access_permitted() better should reject these pages
+		 * either way: otherwise, GUP-fast might succeed in
+		 * cases where ordinary GUP would fail due to VMA access
+		 * permissions.
+		 */
+		if (pte_protnone(pte))
+			goto pte_unmap;
+
+		if (!pte_access_permitted(pte, flags & FOLL_WRITE))
+			goto pte_unmap;
+
+		if (pte_devmap(pte)) {
+			if (unlikely(flags & FOLL_LONGTERM))
+				goto pte_unmap;
+
+			pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
+			if (unlikely(!pgmap)) {
+				undo_dev_pagemap(nr, nr_start, flags, pages);
+				goto pte_unmap;
+			}
+		} else if (pte_special(pte))
+			goto pte_unmap;
+
+		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
+		page = pte_page(pte);
+
+		folio = try_grab_folio(page, 1, flags);
+		if (!folio)
+			goto pte_unmap;
+
+		if (unlikely(folio_is_secretmem(folio))) {
+			gup_put_folio(folio, 1, flags);
+			goto pte_unmap;
+		}
+
+		if (unlikely(pmd_val(pmd) != pmd_val(*pmdp)) ||
+		    unlikely(pte_val(pte) != pte_val(ptep_get(ptep)))) {
+			gup_put_folio(folio, 1, flags);
+			goto pte_unmap;
+		}
+
+		if (!folio_fast_pin_allowed(folio, flags)) {
+			gup_put_folio(folio, 1, flags);
+			goto pte_unmap;
+		}
+
+		if (!pte_write(pte) && gup_must_unshare(NULL, flags, page)) {
+			gup_put_folio(folio, 1, flags);
+			goto pte_unmap;
+		}
+
+		/*
+		 * We need to make the page accessible if and only if we are
+		 * going to access its content (the FOLL_PIN case).  Please
+		 * see Documentation/core-api/pin_user_pages.rst for
+		 * details.
+		 */
+		if (flags & FOLL_PIN) {
+			ret = arch_make_page_accessible(page);
+			if (ret) {
+				gup_put_folio(folio, 1, flags);
+				goto pte_unmap;
+			}
+		}
+		folio_set_referenced(folio);
+		pages[*nr] = page;
+		(*nr)++;
+	} while (ptep++, addr += PAGE_SIZE, addr != end);
+
+	ret = 1;
+
+pte_unmap:
+	if (pgmap)
+		put_dev_pagemap(pgmap);
+	pte_unmap(ptem);
+	return ret;
+}
+#else
+
+/*
+ * If we can't determine whether or not a pte is special, then fail immediately
+ * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
+ * to be special.
+ *
+ * For a futex to be placed on a THP tail page, get_futex_key requires a
+ * get_user_pages_fast_only implementation that can pin pages. Thus it's still
+ * useful to have gup_huge_pmd even if we can't operate on ptes.
+ */
+static int gup_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
+			 unsigned long end, unsigned int flags,
+			 struct page **pages, int *nr)
+{
+	return 0;
+}
+#endif /* CONFIG_ARCH_HAS_PTE_SPECIAL */
+
+#if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
+static int __gup_device_huge(unsigned long pfn, unsigned long addr,
+			     unsigned long end, unsigned int flags,
+			     struct page **pages, int *nr)
+{
+	int nr_start = *nr;
+	struct dev_pagemap *pgmap = NULL;
+
+	do {
+		struct page *page = pfn_to_page(pfn);
+
+		pgmap = get_dev_pagemap(pfn, pgmap);
+		if (unlikely(!pgmap)) {
+			undo_dev_pagemap(nr, nr_start, flags, pages);
+			break;
+		}
+
+		if (!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(page)) {
+			undo_dev_pagemap(nr, nr_start, flags, pages);
+			break;
+		}
+
+		SetPageReferenced(page);
+		pages[*nr] = page;
+		if (unlikely(try_grab_page(page, flags))) {
+			undo_dev_pagemap(nr, nr_start, flags, pages);
+			break;
+		}
+		(*nr)++;
+		pfn++;
+	} while (addr += PAGE_SIZE, addr != end);
+
+	put_dev_pagemap(pgmap);
+	return addr == end;
+}
+
+static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
+{
+	unsigned long fault_pfn;
+	int nr_start = *nr;
+
+	fault_pfn = pmd_pfn(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+	if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
+		return 0;
+
+	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
+		undo_dev_pagemap(nr, nr_start, flags, pages);
+		return 0;
+	}
+	return 1;
+}
+
+static int __gup_device_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
+{
+	unsigned long fault_pfn;
+	int nr_start = *nr;
+
+	fault_pfn = pud_pfn(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
+	if (!__gup_device_huge(fault_pfn, addr, end, flags, pages, nr))
+		return 0;
+
+	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
+		undo_dev_pagemap(nr, nr_start, flags, pages);
+		return 0;
+	}
+	return 1;
+}
+#else
+static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
+{
+	BUILD_BUG();
+	return 0;
+}
+
+static int __gup_device_huge_pud(pud_t pud, pud_t *pudp, unsigned long addr,
+				 unsigned long end, unsigned int flags,
+				 struct page **pages, int *nr)
+{
+	BUILD_BUG();
+	return 0;
+}
+#endif
+
+static int record_subpages(struct page *page, unsigned long addr,
+			   unsigned long end, struct page **pages)
+{
+	int nr;
+
+	for (nr = 0; addr != end; nr++, addr += PAGE_SIZE)
+		pages[nr] = nth_page(page, nr);
+
+	return nr;
+}
+
+#ifdef CONFIG_ARCH_HAS_HUGEPD
+static unsigned long hugepte_addr_end(unsigned long addr, unsigned long end,
+				      unsigned long sz)
+{
+	unsigned long __boundary = (addr + sz) & ~(sz-1);
+	return (__boundary - 1 < end - 1) ? __boundary : end;
+}
+
+static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
+		       unsigned long end, unsigned int flags,
+		       struct page **pages, int *nr)
+{
+	unsigned long pte_end;
+	struct page *page;
+	struct folio *folio;
+	pte_t pte;
+	int refs;
+
+	pte_end = (addr + sz) & ~(sz-1);
+	if (pte_end < end)
+		end = pte_end;
+
+	pte = huge_ptep_get(ptep);
+
+	if (!pte_access_permitted(pte, flags & FOLL_WRITE))
+		return 0;
+
+	/* hugepages are never "special" */
+	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
+
+	page = nth_page(pte_page(pte), (addr & (sz - 1)) >> PAGE_SHIFT);
+	refs = record_subpages(page, addr, end, pages + *nr);
+
+	folio = try_grab_folio(page, refs, flags);
+	if (!folio)
+		return 0;
+
+	if (unlikely(pte_val(pte) != pte_val(ptep_get(ptep)))) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+
+	if (!folio_fast_pin_allowed(folio, flags)) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+
+	if (!pte_write(pte) && gup_must_unshare(NULL, flags, &folio->page)) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+
+	*nr += refs;
+	folio_set_referenced(folio);
+	return 1;
+}
+
+static int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
+		unsigned int pdshift, unsigned long end, unsigned int flags,
+		struct page **pages, int *nr)
+{
+	pte_t *ptep;
+	unsigned long sz = 1UL << hugepd_shift(hugepd);
+	unsigned long next;
+
+	ptep = hugepte_offset(hugepd, addr, pdshift);
+	do {
+		next = hugepte_addr_end(addr, end, sz);
+		if (!gup_hugepte(ptep, sz, addr, end, flags, pages, nr))
+			return 0;
+	} while (ptep++, addr = next, addr != end);
+
+	return 1;
+}
+#else
+static inline int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
+		unsigned int pdshift, unsigned long end, unsigned int flags,
+		struct page **pages, int *nr)
+{
+	return 0;
+}
+#endif /* CONFIG_ARCH_HAS_HUGEPD */
+
+static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
+			unsigned long end, unsigned int flags,
+			struct page **pages, int *nr)
+{
+	struct page *page;
+	struct folio *folio;
+	int refs;
+
+	if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
+		return 0;
+
+	if (pmd_devmap(orig)) {
+		if (unlikely(flags & FOLL_LONGTERM))
+			return 0;
+		return __gup_device_huge_pmd(orig, pmdp, addr, end, flags,
+					     pages, nr);
+	}
+
+	page = nth_page(pmd_page(orig), (addr & ~PMD_MASK) >> PAGE_SHIFT);
+	refs = record_subpages(page, addr, end, pages + *nr);
+
+	folio = try_grab_folio(page, refs, flags);
+	if (!folio)
+		return 0;
+
+	if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+
+	if (!folio_fast_pin_allowed(folio, flags)) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+	if (!pmd_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+
+	*nr += refs;
+	folio_set_referenced(folio);
+	return 1;
+}
+
+static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
+			unsigned long end, unsigned int flags,
+			struct page **pages, int *nr)
+{
+	struct page *page;
+	struct folio *folio;
+	int refs;
+
+	if (!pud_access_permitted(orig, flags & FOLL_WRITE))
+		return 0;
+
+	if (pud_devmap(orig)) {
+		if (unlikely(flags & FOLL_LONGTERM))
+			return 0;
+		return __gup_device_huge_pud(orig, pudp, addr, end, flags,
+					     pages, nr);
+	}
+
+	page = nth_page(pud_page(orig), (addr & ~PUD_MASK) >> PAGE_SHIFT);
+	refs = record_subpages(page, addr, end, pages + *nr);
+
+	folio = try_grab_folio(page, refs, flags);
+	if (!folio)
+		return 0;
+
+	if (unlikely(pud_val(orig) != pud_val(*pudp))) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+
+	if (!folio_fast_pin_allowed(folio, flags)) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+
+	if (!pud_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+
+	*nr += refs;
+	folio_set_referenced(folio);
+	return 1;
+}
+
+static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
+			unsigned long end, unsigned int flags,
+			struct page **pages, int *nr)
+{
+	int refs;
+	struct page *page;
+	struct folio *folio;
+
+	if (!pgd_access_permitted(orig, flags & FOLL_WRITE))
+		return 0;
+
+	BUILD_BUG_ON(pgd_devmap(orig));
+
+	page = nth_page(pgd_page(orig), (addr & ~PGDIR_MASK) >> PAGE_SHIFT);
+	refs = record_subpages(page, addr, end, pages + *nr);
+
+	folio = try_grab_folio(page, refs, flags);
+	if (!folio)
+		return 0;
+
+	if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+
+	if (!pgd_write(orig) && gup_must_unshare(NULL, flags, &folio->page)) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+
+	if (!folio_fast_pin_allowed(folio, flags)) {
+		gup_put_folio(folio, refs, flags);
+		return 0;
+	}
+
+	*nr += refs;
+	folio_set_referenced(folio);
+	return 1;
+}
+
+static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned long end,
+		unsigned int flags, struct page **pages, int *nr)
+{
+	unsigned long next;
+	pmd_t *pmdp;
+
+	pmdp = pmd_offset_lockless(pudp, pud, addr);
+	do {
+		pmd_t pmd = pmdp_get_lockless(pmdp);
+
+		next = pmd_addr_end(addr, end);
+		if (!pmd_present(pmd))
+			return 0;
+
+		if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd) ||
+			     pmd_devmap(pmd))) {
+			/* See gup_pte_range() */
+			if (pmd_protnone(pmd))
+				return 0;
+
+			if (!gup_huge_pmd(pmd, pmdp, addr, next, flags,
+				pages, nr))
+				return 0;
+
+		} else if (unlikely(is_hugepd(__hugepd(pmd_val(pmd))))) {
+			/*
+			 * architecture have different format for hugetlbfs
+			 * pmd format and THP pmd format
+			 */
+			if (!gup_huge_pd(__hugepd(pmd_val(pmd)), addr,
+					 PMD_SHIFT, next, flags, pages, nr))
+				return 0;
+		} else if (!gup_pte_range(pmd, pmdp, addr, next, flags, pages, nr))
+			return 0;
+	} while (pmdp++, addr = next, addr != end);
+
+	return 1;
+}
+
+static int gup_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, unsigned long end,
+			 unsigned int flags, struct page **pages, int *nr)
+{
+	unsigned long next;
+	pud_t *pudp;
+
+	pudp = pud_offset_lockless(p4dp, p4d, addr);
+	do {
+		pud_t pud = READ_ONCE(*pudp);
+
+		next = pud_addr_end(addr, end);
+		if (unlikely(!pud_present(pud)))
+			return 0;
+		if (unlikely(pud_huge(pud) || pud_devmap(pud))) {
+			if (!gup_huge_pud(pud, pudp, addr, next, flags,
+					  pages, nr))
+				return 0;
+		} else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) {
+			if (!gup_huge_pd(__hugepd(pud_val(pud)), addr,
+					 PUD_SHIFT, next, flags, pages, nr))
+				return 0;
+		} else if (!gup_pmd_range(pudp, pud, addr, next, flags, pages, nr))
+			return 0;
+	} while (pudp++, addr = next, addr != end);
+
+	return 1;
+}
+
+static int gup_p4d_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr, unsigned long end,
+			 unsigned int flags, struct page **pages, int *nr)
+{
+	unsigned long next;
+	p4d_t *p4dp;
+
+	p4dp = p4d_offset_lockless(pgdp, pgd, addr);
+	do {
+		p4d_t p4d = READ_ONCE(*p4dp);
+
+		next = p4d_addr_end(addr, end);
+		if (p4d_none(p4d))
+			return 0;
+		BUILD_BUG_ON(p4d_huge(p4d));
+		if (unlikely(is_hugepd(__hugepd(p4d_val(p4d))))) {
+			if (!gup_huge_pd(__hugepd(p4d_val(p4d)), addr,
+					 P4D_SHIFT, next, flags, pages, nr))
+				return 0;
+		} else if (!gup_pud_range(p4dp, p4d, addr, next, flags, pages, nr))
+			return 0;
+	} while (p4dp++, addr = next, addr != end);
+
+	return 1;
+}
+
+static void gup_pgd_range(unsigned long addr, unsigned long end,
+		unsigned int flags, struct page **pages, int *nr)
+{
+	unsigned long next;
+	pgd_t *pgdp;
+
+	pgdp = pgd_offset(current->mm, addr);
+	do {
+		pgd_t pgd = READ_ONCE(*pgdp);
+
+		next = pgd_addr_end(addr, end);
+		if (pgd_none(pgd))
+			return;
+		if (unlikely(pgd_huge(pgd))) {
+			if (!gup_huge_pgd(pgd, pgdp, addr, next, flags,
+					  pages, nr))
+				return;
+		} else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
+			if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
+					 PGDIR_SHIFT, next, flags, pages, nr))
+				return;
+		} else if (!gup_p4d_range(pgdp, pgd, addr, next, flags, pages, nr))
+			return;
+	} while (pgdp++, addr = next, addr != end);
+}
+#else
+static inline void gup_pgd_range(unsigned long addr, unsigned long end,
+		unsigned int flags, struct page **pages, int *nr)
+{
+}
+#endif /* CONFIG_HAVE_FAST_GUP */
+
+#ifndef gup_fast_permitted
+/*
+ * Check if it's allowed to use get_user_pages_fast_only() for the range, or
+ * we need to fall back to the slow version:
+ */
+static bool gup_fast_permitted(unsigned long start, unsigned long end)
+{
+	return true;
+}
+#endif
+
+static unsigned long lockless_pages_from_mm(unsigned long start,
+					    unsigned long end,
+					    unsigned int gup_flags,
+					    struct page **pages)
+{
+	unsigned long flags;
+	int nr_pinned = 0;
+	unsigned seq;
+
+	if (!IS_ENABLED(CONFIG_HAVE_FAST_GUP) ||
+	    !gup_fast_permitted(start, end))
+		return 0;
+
+	if (gup_flags & FOLL_PIN) {
+		seq = raw_read_seqcount(&current->mm->write_protect_seq);
+		if (seq & 1)
+			return 0;
+	}
+
+	/*
+	 * Disable interrupts. The nested form is used, in order to allow full,
+	 * general purpose use of this routine.
+	 *
+	 * With interrupts disabled, we block page table pages from being freed
+	 * from under us. See struct mmu_table_batch comments in
+	 * include/asm-generic/tlb.h for more details.
+	 *
+	 * We do not adopt an rcu_read_lock() here as we also want to block IPIs
+	 * that come from THPs splitting.
+	 */
+	local_irq_save(flags);
+	gup_pgd_range(start, end, gup_flags, pages, &nr_pinned);
+	local_irq_restore(flags);
+
+	/*
+	 * When pinning pages for DMA there could be a concurrent write protect
+	 * from fork() via copy_page_range(), in this case always fail fast GUP.
+	 */
+	if (gup_flags & FOLL_PIN) {
+		if (read_seqcount_retry(&current->mm->write_protect_seq, seq)) {
+			unpin_user_pages_lockless(pages, nr_pinned);
+			return 0;
+		} else {
+			sanity_check_pinned_pages(pages, nr_pinned);
+		}
+	}
+	return nr_pinned;
+}
+
+static int internal_get_user_pages_fast(unsigned long start,
+					unsigned long nr_pages,
+					unsigned int gup_flags,
+					struct page **pages)
+{
+	unsigned long len, end;
+	unsigned long nr_pinned;
+	int locked = 0;
+	int ret;
+
+	if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
+				       FOLL_FORCE | FOLL_PIN | FOLL_GET |
+				       FOLL_FAST_ONLY | FOLL_NOFAULT |
+				       FOLL_PCI_P2PDMA | FOLL_HONOR_NUMA_FAULT)))
+		return -EINVAL;
+
+	if (gup_flags & FOLL_PIN)
+		mm_set_has_pinned_flag(&current->mm->flags);
+
+	if (!(gup_flags & FOLL_FAST_ONLY))
+		might_lock_read(&current->mm->mmap_lock);
+
+	start = untagged_addr(start) & PAGE_MASK;
+	len = nr_pages << PAGE_SHIFT;
+	if (check_add_overflow(start, len, &end))
+		return -EOVERFLOW;
+	if (end > TASK_SIZE_MAX)
+		return -EFAULT;
+	if (unlikely(!access_ok((void __user *)start, len)))
+		return -EFAULT;
+
+	nr_pinned = lockless_pages_from_mm(start, end, gup_flags, pages);
+	if (nr_pinned == nr_pages || gup_flags & FOLL_FAST_ONLY)
+		return nr_pinned;
+
+	/* Slow path: try to get the remaining pages with get_user_pages */
+	start += nr_pinned << PAGE_SHIFT;
+	pages += nr_pinned;
+	ret = __gup_longterm_locked(current->mm, start, nr_pages - nr_pinned,
+				    pages, &locked,
+				    gup_flags | FOLL_TOUCH | FOLL_UNLOCKABLE);
+	if (ret < 0) {
+		/*
+		 * The caller has to unpin the pages we already pinned so
+		 * returning -errno is not an option
+		 */
+		if (nr_pinned)
+			return nr_pinned;
+		return ret;
+	}
+	return ret + nr_pinned;
+}
+
+/**
+ * get_user_pages_fast_only() - pin user pages in memory
+ * @start:      starting user address
+ * @nr_pages:   number of pages from start to pin
+ * @gup_flags:  flags modifying pin behaviour
+ * @pages:      array that receives pointers to the pages pinned.
+ *              Should be at least nr_pages long.
+ *
+ * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
+ * the regular GUP.
+ *
+ * If the architecture does not support this function, simply return with no
+ * pages pinned.
+ *
+ * Careful, careful! COW breaking can go either way, so a non-write
+ * access can get ambiguous page results. If you call this function without
+ * 'write' set, you'd better be sure that you're ok with that ambiguity.
+ */
+int get_user_pages_fast_only(unsigned long start, int nr_pages,
+			     unsigned int gup_flags, struct page **pages)
+{
+	/*
+	 * Internally (within mm/gup.c), gup fast variants must set FOLL_GET,
+	 * because gup fast is always a "pin with a +1 page refcount" request.
+	 *
+	 * FOLL_FAST_ONLY is required in order to match the API description of
+	 * this routine: no fall back to regular ("slow") GUP.
+	 */
+	if (!is_valid_gup_args(pages, NULL, &gup_flags,
+			       FOLL_GET | FOLL_FAST_ONLY))
+		return -EINVAL;
+
+	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
+}
+EXPORT_SYMBOL_GPL(get_user_pages_fast_only);
+
+/**
+ * get_user_pages_fast() - pin user pages in memory
+ * @start:      starting user address
+ * @nr_pages:   number of pages from start to pin
+ * @gup_flags:  flags modifying pin behaviour
+ * @pages:      array that receives pointers to the pages pinned.
+ *              Should be at least nr_pages long.
+ *
+ * Attempt to pin user pages in memory without taking mm->mmap_lock.
+ * If not successful, it will fall back to taking the lock and
+ * calling get_user_pages().
+ *
+ * Returns number of pages pinned. This may be fewer than the number requested.
+ * If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns
+ * -errno.
+ */
+int get_user_pages_fast(unsigned long start, int nr_pages,
+			unsigned int gup_flags, struct page **pages)
+{
+	/*
+	 * The caller may or may not have explicitly set FOLL_GET; either way is
+	 * OK. However, internally (within mm/gup.c), gup fast variants must set
+	 * FOLL_GET, because gup fast is always a "pin with a +1 page refcount"
+	 * request.
+	 */
+	if (!is_valid_gup_args(pages, NULL, &gup_flags, FOLL_GET))
+		return -EINVAL;
+	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
+}
+EXPORT_SYMBOL_GPL(get_user_pages_fast);
+
+/**
+ * pin_user_pages_fast() - pin user pages in memory without taking locks
+ *
+ * @start:      starting user address
+ * @nr_pages:   number of pages from start to pin
+ * @gup_flags:  flags modifying pin behaviour
+ * @pages:      array that receives pointers to the pages pinned.
+ *              Should be at least nr_pages long.
+ *
+ * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See
+ * get_user_pages_fast() for documentation on the function arguments, because
+ * the arguments here are identical.
+ *
+ * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
+ * see Documentation/core-api/pin_user_pages.rst for further details.
+ *
+ * Note that if a zero_page is amongst the returned pages, it will not have
+ * pins in it and unpin_user_page() will not remove pins from it.
+ */
+int pin_user_pages_fast(unsigned long start, int nr_pages,
+			unsigned int gup_flags, struct page **pages)
+{
+	if (!is_valid_gup_args(pages, NULL, &gup_flags, FOLL_PIN))
+		return -EINVAL;
+	return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages);
+}
+EXPORT_SYMBOL_GPL(pin_user_pages_fast);
+
+/**
+ * pin_user_pages_remote() - pin pages of a remote process
+ *
+ * @mm:		mm_struct of target mm
+ * @start:	starting user address
+ * @nr_pages:	number of pages from start to pin
+ * @gup_flags:	flags modifying lookup behaviour
+ * @pages:	array that receives pointers to the pages pinned.
+ *		Should be at least nr_pages long.
+ * @locked:	pointer to lock flag indicating whether lock is held and
+ *		subsequently whether VM_FAULT_RETRY functionality can be
+ *		utilised. Lock must initially be held.
+ *
+ * Nearly the same as get_user_pages_remote(), except that FOLL_PIN is set. See
+ * get_user_pages_remote() for documentation on the function arguments, because
+ * the arguments here are identical.
+ *
+ * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
+ * see Documentation/core-api/pin_user_pages.rst for details.
+ *
+ * Note that if a zero_page is amongst the returned pages, it will not have
+ * pins in it and unpin_user_page*() will not remove pins from it.
+ */
+long pin_user_pages_remote(struct mm_struct *mm,
+			   unsigned long start, unsigned long nr_pages,
+			   unsigned int gup_flags, struct page **pages,
+			   int *locked)
+{
+	int local_locked = 1;
+
+	if (!is_valid_gup_args(pages, locked, &gup_flags,
+			       FOLL_PIN | FOLL_TOUCH | FOLL_REMOTE))
+		return 0;
+	return __gup_longterm_locked(mm, start, nr_pages, pages,
+				     locked ? locked : &local_locked,
+				     gup_flags);
+}
+EXPORT_SYMBOL(pin_user_pages_remote);
+
+/**
+ * pin_user_pages() - pin user pages in memory for use by other devices
+ *
+ * @start:	starting user address
+ * @nr_pages:	number of pages from start to pin
+ * @gup_flags:	flags modifying lookup behaviour
+ * @pages:	array that receives pointers to the pages pinned.
+ *		Should be at least nr_pages long.
+ *
+ * Nearly the same as get_user_pages(), except that FOLL_TOUCH is not set, and
+ * FOLL_PIN is set.
+ *
+ * FOLL_PIN means that the pages must be released via unpin_user_page(). Please
+ * see Documentation/core-api/pin_user_pages.rst for details.
+ *
+ * Note that if a zero_page is amongst the returned pages, it will not have
+ * pins in it and unpin_user_page*() will not remove pins from it.
+ */
+long pin_user_pages(unsigned long start, unsigned long nr_pages,
+		    unsigned int gup_flags, struct page **pages)
+{
+	int locked = 1;
+
+	if (!is_valid_gup_args(pages, NULL, &gup_flags, FOLL_PIN))
+		return 0;
+	return __gup_longterm_locked(current->mm, start, nr_pages,
+				     pages, &locked, gup_flags);
+}
+EXPORT_SYMBOL(pin_user_pages);
+
+/*
+ * pin_user_pages_unlocked() is the FOLL_PIN variant of
+ * get_user_pages_unlocked(). Behavior is the same, except that this one sets
+ * FOLL_PIN and rejects FOLL_GET.
+ *
+ * Note that if a zero_page is amongst the returned pages, it will not have
+ * pins in it and unpin_user_page*() will not remove pins from it.
+ */
+long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
+			     struct page **pages, unsigned int gup_flags)
+{
+	int locked = 0;
+
+	if (!is_valid_gup_args(pages, NULL, &gup_flags,
+			       FOLL_PIN | FOLL_TOUCH | FOLL_UNLOCKABLE))
+		return 0;
+
+	return __gup_longterm_locked(current->mm, start, nr_pages, pages,
+				     &locked, gup_flags);
+}
+EXPORT_SYMBOL(pin_user_pages_unlocked);