Adding upstream version 6.6.15.upstream/6.6.15

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

1 files changed, 960 insertions, 0 deletions

diff --git a/mm/migrate_device.c b/mm/migrate_device.c
new file mode 100644
index 0000000000..8ac1f79f75
--- /dev/null
+++ b/mm/migrate_device.c
@@ -0,0 +1,960 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Device Memory Migration functionality.
+ *
+ * Originally written by Jérôme Glisse.
+ */
+#include <linux/export.h>
+#include <linux/memremap.h>
+#include <linux/migrate.h>
+#include <linux/mm.h>
+#include <linux/mm_inline.h>
+#include <linux/mmu_notifier.h>
+#include <linux/oom.h>
+#include <linux/pagewalk.h>
+#include <linux/rmap.h>
+#include <linux/swapops.h>
+#include <asm/tlbflush.h>
+#include "internal.h"
+
+static int migrate_vma_collect_skip(unsigned long start,
+				    unsigned long end,
+				    struct mm_walk *walk)
+{
+	struct migrate_vma *migrate = walk->private;
+	unsigned long addr;
+
+	for (addr = start; addr < end; addr += PAGE_SIZE) {
+		migrate->dst[migrate->npages] = 0;
+		migrate->src[migrate->npages++] = 0;
+	}
+
+	return 0;
+}
+
+static int migrate_vma_collect_hole(unsigned long start,
+				    unsigned long end,
+				    __always_unused int depth,
+				    struct mm_walk *walk)
+{
+	struct migrate_vma *migrate = walk->private;
+	unsigned long addr;
+
+	/* Only allow populating anonymous memory. */
+	if (!vma_is_anonymous(walk->vma))
+		return migrate_vma_collect_skip(start, end, walk);
+
+	for (addr = start; addr < end; addr += PAGE_SIZE) {
+		migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE;
+		migrate->dst[migrate->npages] = 0;
+		migrate->npages++;
+		migrate->cpages++;
+	}
+
+	return 0;
+}
+
+static int migrate_vma_collect_pmd(pmd_t *pmdp,
+				   unsigned long start,
+				   unsigned long end,
+				   struct mm_walk *walk)
+{
+	struct migrate_vma *migrate = walk->private;
+	struct vm_area_struct *vma = walk->vma;
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long addr = start, unmapped = 0;
+	spinlock_t *ptl;
+	pte_t *ptep;
+
+again:
+	if (pmd_none(*pmdp))
+		return migrate_vma_collect_hole(start, end, -1, walk);
+
+	if (pmd_trans_huge(*pmdp)) {
+		struct page *page;
+
+		ptl = pmd_lock(mm, pmdp);
+		if (unlikely(!pmd_trans_huge(*pmdp))) {
+			spin_unlock(ptl);
+			goto again;
+		}
+
+		page = pmd_page(*pmdp);
+		if (is_huge_zero_page(page)) {
+			spin_unlock(ptl);
+			split_huge_pmd(vma, pmdp, addr);
+		} else {
+			int ret;
+
+			get_page(page);
+			spin_unlock(ptl);
+			if (unlikely(!trylock_page(page)))
+				return migrate_vma_collect_skip(start, end,
+								walk);
+			ret = split_huge_page(page);
+			unlock_page(page);
+			put_page(page);
+			if (ret)
+				return migrate_vma_collect_skip(start, end,
+								walk);
+		}
+	}
+
+	ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
+	if (!ptep)
+		goto again;
+	arch_enter_lazy_mmu_mode();
+
+	for (; addr < end; addr += PAGE_SIZE, ptep++) {
+		unsigned long mpfn = 0, pfn;
+		struct page *page;
+		swp_entry_t entry;
+		pte_t pte;
+
+		pte = ptep_get(ptep);
+
+		if (pte_none(pte)) {
+			if (vma_is_anonymous(vma)) {
+				mpfn = MIGRATE_PFN_MIGRATE;
+				migrate->cpages++;
+			}
+			goto next;
+		}
+
+		if (!pte_present(pte)) {
+			/*
+			 * Only care about unaddressable device page special
+			 * page table entry. Other special swap entries are not
+			 * migratable, and we ignore regular swapped page.
+			 */
+			entry = pte_to_swp_entry(pte);
+			if (!is_device_private_entry(entry))
+				goto next;
+
+			page = pfn_swap_entry_to_page(entry);
+			if (!(migrate->flags &
+				MIGRATE_VMA_SELECT_DEVICE_PRIVATE) ||
+			    page->pgmap->owner != migrate->pgmap_owner)
+				goto next;
+
+			mpfn = migrate_pfn(page_to_pfn(page)) |
+					MIGRATE_PFN_MIGRATE;
+			if (is_writable_device_private_entry(entry))
+				mpfn |= MIGRATE_PFN_WRITE;
+		} else {
+			pfn = pte_pfn(pte);
+			if (is_zero_pfn(pfn) &&
+			    (migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) {
+				mpfn = MIGRATE_PFN_MIGRATE;
+				migrate->cpages++;
+				goto next;
+			}
+			page = vm_normal_page(migrate->vma, addr, pte);
+			if (page && !is_zone_device_page(page) &&
+			    !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
+				goto next;
+			else if (page && is_device_coherent_page(page) &&
+			    (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) ||
+			     page->pgmap->owner != migrate->pgmap_owner))
+				goto next;
+			mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
+			mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
+		}
+
+		/* FIXME support THP */
+		if (!page || !page->mapping || PageTransCompound(page)) {
+			mpfn = 0;
+			goto next;
+		}
+
+		/*
+		 * By getting a reference on the page we pin it and that blocks
+		 * any kind of migration. Side effect is that it "freezes" the
+		 * pte.
+		 *
+		 * We drop this reference after isolating the page from the lru
+		 * for non device page (device page are not on the lru and thus
+		 * can't be dropped from it).
+		 */
+		get_page(page);
+
+		/*
+		 * We rely on trylock_page() to avoid deadlock between
+		 * concurrent migrations where each is waiting on the others
+		 * page lock. If we can't immediately lock the page we fail this
+		 * migration as it is only best effort anyway.
+		 *
+		 * If we can lock the page it's safe to set up a migration entry
+		 * now. In the common case where the page is mapped once in a
+		 * single process setting up the migration entry now is an
+		 * optimisation to avoid walking the rmap later with
+		 * try_to_migrate().
+		 */
+		if (trylock_page(page)) {
+			bool anon_exclusive;
+			pte_t swp_pte;
+
+			flush_cache_page(vma, addr, pte_pfn(pte));
+			anon_exclusive = PageAnon(page) && PageAnonExclusive(page);
+			if (anon_exclusive) {
+				pte = ptep_clear_flush(vma, addr, ptep);
+
+				if (page_try_share_anon_rmap(page)) {
+					set_pte_at(mm, addr, ptep, pte);
+					unlock_page(page);
+					put_page(page);
+					mpfn = 0;
+					goto next;
+				}
+			} else {
+				pte = ptep_get_and_clear(mm, addr, ptep);
+			}
+
+			migrate->cpages++;
+
+			/* Set the dirty flag on the folio now the pte is gone. */
+			if (pte_dirty(pte))
+				folio_mark_dirty(page_folio(page));
+
+			/* Setup special migration page table entry */
+			if (mpfn & MIGRATE_PFN_WRITE)
+				entry = make_writable_migration_entry(
+							page_to_pfn(page));
+			else if (anon_exclusive)
+				entry = make_readable_exclusive_migration_entry(
+							page_to_pfn(page));
+			else
+				entry = make_readable_migration_entry(
+							page_to_pfn(page));
+			if (pte_present(pte)) {
+				if (pte_young(pte))
+					entry = make_migration_entry_young(entry);
+				if (pte_dirty(pte))
+					entry = make_migration_entry_dirty(entry);
+			}
+			swp_pte = swp_entry_to_pte(entry);
+			if (pte_present(pte)) {
+				if (pte_soft_dirty(pte))
+					swp_pte = pte_swp_mksoft_dirty(swp_pte);
+				if (pte_uffd_wp(pte))
+					swp_pte = pte_swp_mkuffd_wp(swp_pte);
+			} else {
+				if (pte_swp_soft_dirty(pte))
+					swp_pte = pte_swp_mksoft_dirty(swp_pte);
+				if (pte_swp_uffd_wp(pte))
+					swp_pte = pte_swp_mkuffd_wp(swp_pte);
+			}
+			set_pte_at(mm, addr, ptep, swp_pte);
+
+			/*
+			 * This is like regular unmap: we remove the rmap and
+			 * drop page refcount. Page won't be freed, as we took
+			 * a reference just above.
+			 */
+			page_remove_rmap(page, vma, false);
+			put_page(page);
+
+			if (pte_present(pte))
+				unmapped++;
+		} else {
+			put_page(page);
+			mpfn = 0;
+		}
+
+next:
+		migrate->dst[migrate->npages] = 0;
+		migrate->src[migrate->npages++] = mpfn;
+	}
+
+	/* Only flush the TLB if we actually modified any entries */
+	if (unmapped)
+		flush_tlb_range(walk->vma, start, end);
+
+	arch_leave_lazy_mmu_mode();
+	pte_unmap_unlock(ptep - 1, ptl);
+
+	return 0;
+}
+
+static const struct mm_walk_ops migrate_vma_walk_ops = {
+	.pmd_entry		= migrate_vma_collect_pmd,
+	.pte_hole		= migrate_vma_collect_hole,
+	.walk_lock		= PGWALK_RDLOCK,
+};
+
+/*
+ * migrate_vma_collect() - collect pages over a range of virtual addresses
+ * @migrate: migrate struct containing all migration information
+ *
+ * This will walk the CPU page table. For each virtual address backed by a
+ * valid page, it updates the src array and takes a reference on the page, in
+ * order to pin the page until we lock it and unmap it.
+ */
+static void migrate_vma_collect(struct migrate_vma *migrate)
+{
+	struct mmu_notifier_range range;
+
+	/*
+	 * Note that the pgmap_owner is passed to the mmu notifier callback so
+	 * that the registered device driver can skip invalidating device
+	 * private page mappings that won't be migrated.
+	 */
+	mmu_notifier_range_init_owner(&range, MMU_NOTIFY_MIGRATE, 0,
+		migrate->vma->vm_mm, migrate->start, migrate->end,
+		migrate->pgmap_owner);
+	mmu_notifier_invalidate_range_start(&range);
+
+	walk_page_range(migrate->vma->vm_mm, migrate->start, migrate->end,
+			&migrate_vma_walk_ops, migrate);
+
+	mmu_notifier_invalidate_range_end(&range);
+	migrate->end = migrate->start + (migrate->npages << PAGE_SHIFT);
+}
+
+/*
+ * migrate_vma_check_page() - check if page is pinned or not
+ * @page: struct page to check
+ *
+ * Pinned pages cannot be migrated. This is the same test as in
+ * folio_migrate_mapping(), except that here we allow migration of a
+ * ZONE_DEVICE page.
+ */
+static bool migrate_vma_check_page(struct page *page, struct page *fault_page)
+{
+	/*
+	 * One extra ref because caller holds an extra reference, either from
+	 * isolate_lru_page() for a regular page, or migrate_vma_collect() for
+	 * a device page.
+	 */
+	int extra = 1 + (page == fault_page);
+
+	/*
+	 * FIXME support THP (transparent huge page), it is bit more complex to
+	 * check them than regular pages, because they can be mapped with a pmd
+	 * or with a pte (split pte mapping).
+	 */
+	if (PageCompound(page))
+		return false;
+
+	/* Page from ZONE_DEVICE have one extra reference */
+	if (is_zone_device_page(page))
+		extra++;
+
+	/* For file back page */
+	if (page_mapping(page))
+		extra += 1 + page_has_private(page);
+
+	if ((page_count(page) - extra) > page_mapcount(page))
+		return false;
+
+	return true;
+}
+
+/*
+ * Unmaps pages for migration. Returns number of source pfns marked as
+ * migrating.
+ */
+static unsigned long migrate_device_unmap(unsigned long *src_pfns,
+					  unsigned long npages,
+					  struct page *fault_page)
+{
+	unsigned long i, restore = 0;
+	bool allow_drain = true;
+	unsigned long unmapped = 0;
+
+	lru_add_drain();
+
+	for (i = 0; i < npages; i++) {
+		struct page *page = migrate_pfn_to_page(src_pfns[i]);
+		struct folio *folio;
+
+		if (!page) {
+			if (src_pfns[i] & MIGRATE_PFN_MIGRATE)
+				unmapped++;
+			continue;
+		}
+
+		/* ZONE_DEVICE pages are not on LRU */
+		if (!is_zone_device_page(page)) {
+			if (!PageLRU(page) && allow_drain) {
+				/* Drain CPU's lru cache */
+				lru_add_drain_all();
+				allow_drain = false;
+			}
+
+			if (!isolate_lru_page(page)) {
+				src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
+				restore++;
+				continue;
+			}
+
+			/* Drop the reference we took in collect */
+			put_page(page);
+		}
+
+		folio = page_folio(page);
+		if (folio_mapped(folio))
+			try_to_migrate(folio, 0);
+
+		if (page_mapped(page) ||
+		    !migrate_vma_check_page(page, fault_page)) {
+			if (!is_zone_device_page(page)) {
+				get_page(page);
+				putback_lru_page(page);
+			}
+
+			src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
+			restore++;
+			continue;
+		}
+
+		unmapped++;
+	}
+
+	for (i = 0; i < npages && restore; i++) {
+		struct page *page = migrate_pfn_to_page(src_pfns[i]);
+		struct folio *folio;
+
+		if (!page || (src_pfns[i] & MIGRATE_PFN_MIGRATE))
+			continue;
+
+		folio = page_folio(page);
+		remove_migration_ptes(folio, folio, false);
+
+		src_pfns[i] = 0;
+		folio_unlock(folio);
+		folio_put(folio);
+		restore--;
+	}
+
+	return unmapped;
+}
+
+/*
+ * migrate_vma_unmap() - replace page mapping with special migration pte entry
+ * @migrate: migrate struct containing all migration information
+ *
+ * Isolate pages from the LRU and replace mappings (CPU page table pte) with a
+ * special migration pte entry and check if it has been pinned. Pinned pages are
+ * restored because we cannot migrate them.
+ *
+ * This is the last step before we call the device driver callback to allocate
+ * destination memory and copy contents of original page over to new page.
+ */
+static void migrate_vma_unmap(struct migrate_vma *migrate)
+{
+	migrate->cpages = migrate_device_unmap(migrate->src, migrate->npages,
+					migrate->fault_page);
+}
+
+/**
+ * migrate_vma_setup() - prepare to migrate a range of memory
+ * @args: contains the vma, start, and pfns arrays for the migration
+ *
+ * Returns: negative errno on failures, 0 when 0 or more pages were migrated
+ * without an error.
+ *
+ * Prepare to migrate a range of memory virtual address range by collecting all
+ * the pages backing each virtual address in the range, saving them inside the
+ * src array.  Then lock those pages and unmap them. Once the pages are locked
+ * and unmapped, check whether each page is pinned or not.  Pages that aren't
+ * pinned have the MIGRATE_PFN_MIGRATE flag set (by this function) in the
+ * corresponding src array entry.  Then restores any pages that are pinned, by
+ * remapping and unlocking those pages.
+ *
+ * The caller should then allocate destination memory and copy source memory to
+ * it for all those entries (ie with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE
+ * flag set).  Once these are allocated and copied, the caller must update each
+ * corresponding entry in the dst array with the pfn value of the destination
+ * page and with MIGRATE_PFN_VALID. Destination pages must be locked via
+ * lock_page().
+ *
+ * Note that the caller does not have to migrate all the pages that are marked
+ * with MIGRATE_PFN_MIGRATE flag in src array unless this is a migration from
+ * device memory to system memory.  If the caller cannot migrate a device page
+ * back to system memory, then it must return VM_FAULT_SIGBUS, which has severe
+ * consequences for the userspace process, so it must be avoided if at all
+ * possible.
+ *
+ * For empty entries inside CPU page table (pte_none() or pmd_none() is true) we
+ * do set MIGRATE_PFN_MIGRATE flag inside the corresponding source array thus
+ * allowing the caller to allocate device memory for those unbacked virtual
+ * addresses.  For this the caller simply has to allocate device memory and
+ * properly set the destination entry like for regular migration.  Note that
+ * this can still fail, and thus inside the device driver you must check if the
+ * migration was successful for those entries after calling migrate_vma_pages(),
+ * just like for regular migration.
+ *
+ * After that, the callers must call migrate_vma_pages() to go over each entry
+ * in the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag
+ * set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag set,
+ * then migrate_vma_pages() to migrate struct page information from the source
+ * struct page to the destination struct page.  If it fails to migrate the
+ * struct page information, then it clears the MIGRATE_PFN_MIGRATE flag in the
+ * src array.
+ *
+ * At this point all successfully migrated pages have an entry in the src
+ * array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the dst
+ * array entry with MIGRATE_PFN_VALID flag set.
+ *
+ * Once migrate_vma_pages() returns the caller may inspect which pages were
+ * successfully migrated, and which were not.  Successfully migrated pages will
+ * have the MIGRATE_PFN_MIGRATE flag set for their src array entry.
+ *
+ * It is safe to update device page table after migrate_vma_pages() because
+ * both destination and source page are still locked, and the mmap_lock is held
+ * in read mode (hence no one can unmap the range being migrated).
+ *
+ * Once the caller is done cleaning up things and updating its page table (if it
+ * chose to do so, this is not an obligation) it finally calls
+ * migrate_vma_finalize() to update the CPU page table to point to new pages
+ * for successfully migrated pages or otherwise restore the CPU page table to
+ * point to the original source pages.
+ */
+int migrate_vma_setup(struct migrate_vma *args)
+{
+	long nr_pages = (args->end - args->start) >> PAGE_SHIFT;
+
+	args->start &= PAGE_MASK;
+	args->end &= PAGE_MASK;
+	if (!args->vma || is_vm_hugetlb_page(args->vma) ||
+	    (args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(args->vma))
+		return -EINVAL;
+	if (nr_pages <= 0)
+		return -EINVAL;
+	if (args->start < args->vma->vm_start ||
+	    args->start >= args->vma->vm_end)
+		return -EINVAL;
+	if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end)
+		return -EINVAL;
+	if (!args->src || !args->dst)
+		return -EINVAL;
+	if (args->fault_page && !is_device_private_page(args->fault_page))
+		return -EINVAL;
+
+	memset(args->src, 0, sizeof(*args->src) * nr_pages);
+	args->cpages = 0;
+	args->npages = 0;
+
+	migrate_vma_collect(args);
+
+	if (args->cpages)
+		migrate_vma_unmap(args);
+
+	/*
+	 * At this point pages are locked and unmapped, and thus they have
+	 * stable content and can safely be copied to destination memory that
+	 * is allocated by the drivers.
+	 */
+	return 0;
+
+}
+EXPORT_SYMBOL(migrate_vma_setup);
+
+/*
+ * This code closely matches the code in:
+ *   __handle_mm_fault()
+ *     handle_pte_fault()
+ *       do_anonymous_page()
+ * to map in an anonymous zero page but the struct page will be a ZONE_DEVICE
+ * private or coherent page.
+ */
+static void migrate_vma_insert_page(struct migrate_vma *migrate,
+				    unsigned long addr,
+				    struct page *page,
+				    unsigned long *src)
+{
+	struct vm_area_struct *vma = migrate->vma;
+	struct mm_struct *mm = vma->vm_mm;
+	bool flush = false;
+	spinlock_t *ptl;
+	pte_t entry;
+	pgd_t *pgdp;
+	p4d_t *p4dp;
+	pud_t *pudp;
+	pmd_t *pmdp;
+	pte_t *ptep;
+	pte_t orig_pte;
+
+	/* Only allow populating anonymous memory */
+	if (!vma_is_anonymous(vma))
+		goto abort;
+
+	pgdp = pgd_offset(mm, addr);
+	p4dp = p4d_alloc(mm, pgdp, addr);
+	if (!p4dp)
+		goto abort;
+	pudp = pud_alloc(mm, p4dp, addr);
+	if (!pudp)
+		goto abort;
+	pmdp = pmd_alloc(mm, pudp, addr);
+	if (!pmdp)
+		goto abort;
+	if (pmd_trans_huge(*pmdp) || pmd_devmap(*pmdp))
+		goto abort;
+	if (pte_alloc(mm, pmdp))
+		goto abort;
+	if (unlikely(anon_vma_prepare(vma)))
+		goto abort;
+	if (mem_cgroup_charge(page_folio(page), vma->vm_mm, GFP_KERNEL))
+		goto abort;
+
+	/*
+	 * The memory barrier inside __SetPageUptodate makes sure that
+	 * preceding stores to the page contents become visible before
+	 * the set_pte_at() write.
+	 */
+	__SetPageUptodate(page);
+
+	if (is_device_private_page(page)) {
+		swp_entry_t swp_entry;
+
+		if (vma->vm_flags & VM_WRITE)
+			swp_entry = make_writable_device_private_entry(
+						page_to_pfn(page));
+		else
+			swp_entry = make_readable_device_private_entry(
+						page_to_pfn(page));
+		entry = swp_entry_to_pte(swp_entry);
+	} else {
+		if (is_zone_device_page(page) &&
+		    !is_device_coherent_page(page)) {
+			pr_warn_once("Unsupported ZONE_DEVICE page type.\n");
+			goto abort;
+		}
+		entry = mk_pte(page, vma->vm_page_prot);
+		if (vma->vm_flags & VM_WRITE)
+			entry = pte_mkwrite(pte_mkdirty(entry), vma);
+	}
+
+	ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
+	if (!ptep)
+		goto abort;
+	orig_pte = ptep_get(ptep);
+
+	if (check_stable_address_space(mm))
+		goto unlock_abort;
+
+	if (pte_present(orig_pte)) {
+		unsigned long pfn = pte_pfn(orig_pte);
+
+		if (!is_zero_pfn(pfn))
+			goto unlock_abort;
+		flush = true;
+	} else if (!pte_none(orig_pte))
+		goto unlock_abort;
+
+	/*
+	 * Check for userfaultfd but do not deliver the fault. Instead,
+	 * just back off.
+	 */
+	if (userfaultfd_missing(vma))
+		goto unlock_abort;
+
+	inc_mm_counter(mm, MM_ANONPAGES);
+	page_add_new_anon_rmap(page, vma, addr);
+	if (!is_zone_device_page(page))
+		lru_cache_add_inactive_or_unevictable(page, vma);
+	get_page(page);
+
+	if (flush) {
+		flush_cache_page(vma, addr, pte_pfn(orig_pte));
+		ptep_clear_flush(vma, addr, ptep);
+		set_pte_at_notify(mm, addr, ptep, entry);
+		update_mmu_cache(vma, addr, ptep);
+	} else {
+		/* No need to invalidate - it was non-present before */
+		set_pte_at(mm, addr, ptep, entry);
+		update_mmu_cache(vma, addr, ptep);
+	}
+
+	pte_unmap_unlock(ptep, ptl);
+	*src = MIGRATE_PFN_MIGRATE;
+	return;
+
+unlock_abort:
+	pte_unmap_unlock(ptep, ptl);
+abort:
+	*src &= ~MIGRATE_PFN_MIGRATE;
+}
+
+static void __migrate_device_pages(unsigned long *src_pfns,
+				unsigned long *dst_pfns, unsigned long npages,
+				struct migrate_vma *migrate)
+{
+	struct mmu_notifier_range range;
+	unsigned long i;
+	bool notified = false;
+
+	for (i = 0; i < npages; i++) {
+		struct page *newpage = migrate_pfn_to_page(dst_pfns[i]);
+		struct page *page = migrate_pfn_to_page(src_pfns[i]);
+		struct address_space *mapping;
+		int r;
+
+		if (!newpage) {
+			src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
+			continue;
+		}
+
+		if (!page) {
+			unsigned long addr;
+
+			if (!(src_pfns[i] & MIGRATE_PFN_MIGRATE))
+				continue;
+
+			/*
+			 * The only time there is no vma is when called from
+			 * migrate_device_coherent_page(). However this isn't
+			 * called if the page could not be unmapped.
+			 */
+			VM_BUG_ON(!migrate);
+			addr = migrate->start + i*PAGE_SIZE;
+			if (!notified) {
+				notified = true;
+
+				mmu_notifier_range_init_owner(&range,
+					MMU_NOTIFY_MIGRATE, 0,
+					migrate->vma->vm_mm, addr, migrate->end,
+					migrate->pgmap_owner);
+				mmu_notifier_invalidate_range_start(&range);
+			}
+			migrate_vma_insert_page(migrate, addr, newpage,
+						&src_pfns[i]);
+			continue;
+		}
+
+		mapping = page_mapping(page);
+
+		if (is_device_private_page(newpage) ||
+		    is_device_coherent_page(newpage)) {
+			if (mapping) {
+				struct folio *folio;
+
+				folio = page_folio(page);
+
+				/*
+				 * For now only support anonymous memory migrating to
+				 * device private or coherent memory.
+				 *
+				 * Try to get rid of swap cache if possible.
+				 */
+				if (!folio_test_anon(folio) ||
+				    !folio_free_swap(folio)) {
+					src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
+					continue;
+				}
+			}
+		} else if (is_zone_device_page(newpage)) {
+			/*
+			 * Other types of ZONE_DEVICE page are not supported.
+			 */
+			src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
+			continue;
+		}
+
+		if (migrate && migrate->fault_page == page)
+			r = migrate_folio_extra(mapping, page_folio(newpage),
+						page_folio(page),
+						MIGRATE_SYNC_NO_COPY, 1);
+		else
+			r = migrate_folio(mapping, page_folio(newpage),
+					page_folio(page), MIGRATE_SYNC_NO_COPY);
+		if (r != MIGRATEPAGE_SUCCESS)
+			src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
+	}
+
+	if (notified)
+		mmu_notifier_invalidate_range_end(&range);
+}
+
+/**
+ * migrate_device_pages() - migrate meta-data from src page to dst page
+ * @src_pfns: src_pfns returned from migrate_device_range()
+ * @dst_pfns: array of pfns allocated by the driver to migrate memory to
+ * @npages: number of pages in the range
+ *
+ * Equivalent to migrate_vma_pages(). This is called to migrate struct page
+ * meta-data from source struct page to destination.
+ */
+void migrate_device_pages(unsigned long *src_pfns, unsigned long *dst_pfns,
+			unsigned long npages)
+{
+	__migrate_device_pages(src_pfns, dst_pfns, npages, NULL);
+}
+EXPORT_SYMBOL(migrate_device_pages);
+
+/**
+ * migrate_vma_pages() - migrate meta-data from src page to dst page
+ * @migrate: migrate struct containing all migration information
+ *
+ * This migrates struct page meta-data from source struct page to destination
+ * struct page. This effectively finishes the migration from source page to the
+ * destination page.
+ */
+void migrate_vma_pages(struct migrate_vma *migrate)
+{
+	__migrate_device_pages(migrate->src, migrate->dst, migrate->npages, migrate);
+}
+EXPORT_SYMBOL(migrate_vma_pages);
+
+/*
+ * migrate_device_finalize() - complete page migration
+ * @src_pfns: src_pfns returned from migrate_device_range()
+ * @dst_pfns: array of pfns allocated by the driver to migrate memory to
+ * @npages: number of pages in the range
+ *
+ * Completes migration of the page by removing special migration entries.
+ * Drivers must ensure copying of page data is complete and visible to the CPU
+ * before calling this.
+ */
+void migrate_device_finalize(unsigned long *src_pfns,
+			unsigned long *dst_pfns, unsigned long npages)
+{
+	unsigned long i;
+
+	for (i = 0; i < npages; i++) {
+		struct folio *dst, *src;
+		struct page *newpage = migrate_pfn_to_page(dst_pfns[i]);
+		struct page *page = migrate_pfn_to_page(src_pfns[i]);
+
+		if (!page) {
+			if (newpage) {
+				unlock_page(newpage);
+				put_page(newpage);
+			}
+			continue;
+		}
+
+		if (!(src_pfns[i] & MIGRATE_PFN_MIGRATE) || !newpage) {
+			if (newpage) {
+				unlock_page(newpage);
+				put_page(newpage);
+			}
+			newpage = page;
+		}
+
+		src = page_folio(page);
+		dst = page_folio(newpage);
+		remove_migration_ptes(src, dst, false);
+		folio_unlock(src);
+
+		if (is_zone_device_page(page))
+			put_page(page);
+		else
+			putback_lru_page(page);
+
+		if (newpage != page) {
+			unlock_page(newpage);
+			if (is_zone_device_page(newpage))
+				put_page(newpage);
+			else
+				putback_lru_page(newpage);
+		}
+	}
+}
+EXPORT_SYMBOL(migrate_device_finalize);
+
+/**
+ * migrate_vma_finalize() - restore CPU page table entry
+ * @migrate: migrate struct containing all migration information
+ *
+ * This replaces the special migration pte entry with either a mapping to the
+ * new page if migration was successful for that page, or to the original page
+ * otherwise.
+ *
+ * This also unlocks the pages and puts them back on the lru, or drops the extra
+ * refcount, for device pages.
+ */
+void migrate_vma_finalize(struct migrate_vma *migrate)
+{
+	migrate_device_finalize(migrate->src, migrate->dst, migrate->npages);
+}
+EXPORT_SYMBOL(migrate_vma_finalize);
+
+/**
+ * migrate_device_range() - migrate device private pfns to normal memory.
+ * @src_pfns: array large enough to hold migrating source device private pfns.
+ * @start: starting pfn in the range to migrate.
+ * @npages: number of pages to migrate.
+ *
+ * migrate_vma_setup() is similar in concept to migrate_vma_setup() except that
+ * instead of looking up pages based on virtual address mappings a range of
+ * device pfns that should be migrated to system memory is used instead.
+ *
+ * This is useful when a driver needs to free device memory but doesn't know the
+ * virtual mappings of every page that may be in device memory. For example this
+ * is often the case when a driver is being unloaded or unbound from a device.
+ *
+ * Like migrate_vma_setup() this function will take a reference and lock any
+ * migrating pages that aren't free before unmapping them. Drivers may then
+ * allocate destination pages and start copying data from the device to CPU
+ * memory before calling migrate_device_pages().
+ */
+int migrate_device_range(unsigned long *src_pfns, unsigned long start,
+			unsigned long npages)
+{
+	unsigned long i, pfn;
+
+	for (pfn = start, i = 0; i < npages; pfn++, i++) {
+		struct page *page = pfn_to_page(pfn);
+
+		if (!get_page_unless_zero(page)) {
+			src_pfns[i] = 0;
+			continue;
+		}
+
+		if (!trylock_page(page)) {
+			src_pfns[i] = 0;
+			put_page(page);
+			continue;
+		}
+
+		src_pfns[i] = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
+	}
+
+	migrate_device_unmap(src_pfns, npages, NULL);
+
+	return 0;
+}
+EXPORT_SYMBOL(migrate_device_range);
+
+/*
+ * Migrate a device coherent page back to normal memory. The caller should have
+ * a reference on page which will be copied to the new page if migration is
+ * successful or dropped on failure.
+ */
+int migrate_device_coherent_page(struct page *page)
+{
+	unsigned long src_pfn, dst_pfn = 0;
+	struct page *dpage;
+
+	WARN_ON_ONCE(PageCompound(page));
+
+	lock_page(page);
+	src_pfn = migrate_pfn(page_to_pfn(page)) | MIGRATE_PFN_MIGRATE;
+
+	/*
+	 * We don't have a VMA and don't need to walk the page tables to find
+	 * the source page. So call migrate_vma_unmap() directly to unmap the
+	 * page as migrate_vma_setup() will fail if args.vma == NULL.
+	 */
+	migrate_device_unmap(&src_pfn, 1, NULL);
+	if (!(src_pfn & MIGRATE_PFN_MIGRATE))
+		return -EBUSY;
+
+	dpage = alloc_page(GFP_USER | __GFP_NOWARN);
+	if (dpage) {
+		lock_page(dpage);
+		dst_pfn = migrate_pfn(page_to_pfn(dpage));
+	}
+
+	migrate_device_pages(&src_pfn, &dst_pfn, 1);
+	if (src_pfn & MIGRATE_PFN_MIGRATE)
+		copy_highpage(dpage, page);
+	migrate_device_finalize(&src_pfn, &dst_pfn, 1);
+
+	if (src_pfn & MIGRATE_PFN_MIGRATE)
+		return 0;
+	return -EBUSY;
+}