diff options
Diffstat (limited to 'mm/migrate_device.c')
| -rw-r--r-- | mm/migrate_device.c | 1491 |
1 files changed, 1491 insertions, 0 deletions
diff --git a/mm/migrate_device.c b/mm/migrate_device.c new file mode 100644 index 000000000000..23379663b1e1 --- /dev/null +++ b/mm/migrate_device.c @@ -0,0 +1,1491 @@ +// 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/leafops.h> +#include <linux/pgalloc.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); + + if (thp_migration_supported() && + (migrate->flags & MIGRATE_VMA_SELECT_COMPOUND) && + (IS_ALIGNED(start, HPAGE_PMD_SIZE) && + IS_ALIGNED(end, HPAGE_PMD_SIZE))) { + migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE | + MIGRATE_PFN_COMPOUND; + migrate->dst[migrate->npages] = 0; + migrate->npages++; + migrate->cpages++; + + /* + * Collect the remaining entries as holes, in case we + * need to split later + */ + return migrate_vma_collect_skip(start + PAGE_SIZE, 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; +} + +/** + * migrate_vma_split_folio() - Helper function to split a THP folio + * @folio: the folio to split + * @fault_page: struct page associated with the fault if any + * + * Returns 0 on success + */ +static int migrate_vma_split_folio(struct folio *folio, + struct page *fault_page) +{ + int ret; + struct folio *fault_folio = fault_page ? page_folio(fault_page) : NULL; + struct folio *new_fault_folio = NULL; + + if (folio != fault_folio) { + folio_get(folio); + folio_lock(folio); + } + + ret = split_folio(folio); + if (ret) { + if (folio != fault_folio) { + folio_unlock(folio); + folio_put(folio); + } + return ret; + } + + new_fault_folio = fault_page ? page_folio(fault_page) : NULL; + + /* + * Ensure the lock is held on the correct + * folio after the split + */ + if (!new_fault_folio) { + folio_unlock(folio); + folio_put(folio); + } else if (folio != new_fault_folio) { + if (new_fault_folio != fault_folio) { + folio_get(new_fault_folio); + folio_lock(new_fault_folio); + } + folio_unlock(folio); + folio_put(folio); + } + + return 0; +} + +/** migrate_vma_collect_huge_pmd - collect THP pages without splitting the + * folio for device private pages. + * @pmdp: pointer to pmd entry + * @start: start address of the range for migration + * @end: end address of the range for migration + * @walk: mm_walk callback structure + * @fault_folio: folio associated with the fault if any + * + * Collect the huge pmd entry at @pmdp for migration and set the + * MIGRATE_PFN_COMPOUND flag in the migrate src entry to indicate that + * migration will occur at HPAGE_PMD granularity + */ +static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start, + unsigned long end, struct mm_walk *walk, + struct folio *fault_folio) +{ + struct mm_struct *mm = walk->mm; + struct folio *folio; + struct migrate_vma *migrate = walk->private; + spinlock_t *ptl; + int ret; + unsigned long write = 0; + + ptl = pmd_lock(mm, pmdp); + if (pmd_none(*pmdp)) { + spin_unlock(ptl); + return migrate_vma_collect_hole(start, end, -1, walk); + } + + if (pmd_trans_huge(*pmdp)) { + if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) { + spin_unlock(ptl); + return migrate_vma_collect_skip(start, end, walk); + } + + folio = pmd_folio(*pmdp); + if (is_huge_zero_folio(folio)) { + spin_unlock(ptl); + return migrate_vma_collect_hole(start, end, -1, walk); + } + if (pmd_write(*pmdp)) + write = MIGRATE_PFN_WRITE; + } else if (!pmd_present(*pmdp)) { + const softleaf_t entry = softleaf_from_pmd(*pmdp); + + folio = softleaf_to_folio(entry); + + if (!softleaf_is_device_private(entry) || + !(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_PRIVATE) || + (folio->pgmap->owner != migrate->pgmap_owner)) { + spin_unlock(ptl); + return migrate_vma_collect_skip(start, end, walk); + } + + if (softleaf_is_migration(entry)) { + migration_entry_wait_on_locked(entry, ptl); + spin_unlock(ptl); + return -EAGAIN; + } + + if (softleaf_is_device_private_write(entry)) + write = MIGRATE_PFN_WRITE; + } else { + spin_unlock(ptl); + return -EAGAIN; + } + + folio_get(folio); + if (folio != fault_folio && unlikely(!folio_trylock(folio))) { + spin_unlock(ptl); + folio_put(folio); + return migrate_vma_collect_skip(start, end, walk); + } + + if (thp_migration_supported() && + (migrate->flags & MIGRATE_VMA_SELECT_COMPOUND) && + (IS_ALIGNED(start, HPAGE_PMD_SIZE) && + IS_ALIGNED(end, HPAGE_PMD_SIZE))) { + + struct page_vma_mapped_walk pvmw = { + .ptl = ptl, + .address = start, + .pmd = pmdp, + .vma = walk->vma, + }; + + unsigned long pfn = page_to_pfn(folio_page(folio, 0)); + + migrate->src[migrate->npages] = migrate_pfn(pfn) | write + | MIGRATE_PFN_MIGRATE + | MIGRATE_PFN_COMPOUND; + migrate->dst[migrate->npages++] = 0; + migrate->cpages++; + ret = set_pmd_migration_entry(&pvmw, folio_page(folio, 0)); + if (ret) { + migrate->npages--; + migrate->cpages--; + migrate->src[migrate->npages] = 0; + migrate->dst[migrate->npages] = 0; + goto fallback; + } + migrate_vma_collect_skip(start + PAGE_SIZE, end, walk); + spin_unlock(ptl); + return 0; + } + +fallback: + spin_unlock(ptl); + if (!folio_test_large(folio)) + goto done; + ret = split_folio(folio); + if (fault_folio != folio) + folio_unlock(folio); + folio_put(folio); + if (ret) + return migrate_vma_collect_skip(start, end, walk); + if (pmd_none(pmdp_get_lockless(pmdp))) + return migrate_vma_collect_hole(start, end, -1, walk); + +done: + return -ENOENT; +} + +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; + struct folio *fault_folio = migrate->fault_page ? + page_folio(migrate->fault_page) : NULL; + pte_t *ptep; + +again: + if (pmd_trans_huge(*pmdp) || !pmd_present(*pmdp)) { + int ret = migrate_vma_collect_huge_pmd(pmdp, start, end, walk, fault_folio); + + if (ret == -EAGAIN) + goto again; + if (ret == 0) + return 0; + } + + ptep = pte_offset_map_lock(mm, pmdp, start, &ptl); + if (!ptep) + goto again; + arch_enter_lazy_mmu_mode(); + ptep += (addr - start) / PAGE_SIZE; + + for (; addr < end; addr += PAGE_SIZE, ptep++) { + struct dev_pagemap *pgmap; + unsigned long mpfn = 0, pfn; + struct folio *folio; + struct page *page; + softleaf_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 = softleaf_from_pte(pte); + if (!softleaf_is_device_private(entry)) + goto next; + + page = softleaf_to_page(entry); + pgmap = page_pgmap(page); + if (!(migrate->flags & + MIGRATE_VMA_SELECT_DEVICE_PRIVATE) || + pgmap->owner != migrate->pgmap_owner) + goto next; + + folio = page_folio(page); + if (folio_test_large(folio)) { + int ret; + + arch_leave_lazy_mmu_mode(); + pte_unmap_unlock(ptep, ptl); + ret = migrate_vma_split_folio(folio, + migrate->fault_page); + + if (ret) { + if (unmapped) + flush_tlb_range(walk->vma, start, end); + + return migrate_vma_collect_skip(addr, end, walk); + } + + goto again; + } + + mpfn = migrate_pfn(page_to_pfn(page)) | + MIGRATE_PFN_MIGRATE; + if (softleaf_is_device_private_write(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)) { + pgmap = page_pgmap(page); + + if (!(migrate->flags & + MIGRATE_VMA_SELECT_DEVICE_COHERENT) || + pgmap->owner != migrate->pgmap_owner) + goto next; + } + folio = page ? page_folio(page) : NULL; + if (folio && folio_test_large(folio)) { + int ret; + + arch_leave_lazy_mmu_mode(); + pte_unmap_unlock(ptep, ptl); + ret = migrate_vma_split_folio(folio, + migrate->fault_page); + + if (ret) { + if (unmapped) + flush_tlb_range(walk->vma, start, end); + + return migrate_vma_collect_skip(addr, end, walk); + } + + goto again; + } + mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE; + mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0; + } + + if (!page || !page->mapping) { + mpfn = 0; + goto next; + } + + /* + * By getting a reference on the folio 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 folio from the lru + * for non device folio (device folio are not on the lru and thus + * can't be dropped from it). + */ + folio = page_folio(page); + folio_get(folio); + + /* + * We rely on folio_trylock() to avoid deadlock between + * concurrent migrations where each is waiting on the others + * folio lock. If we can't immediately lock the folio we fail this + * migration as it is only best effort anyway. + * + * If we can lock the folio it's safe to set up a migration entry + * now. In the common case where the folio 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 (fault_folio == folio || folio_trylock(folio)) { + bool anon_exclusive; + pte_t swp_pte; + + flush_cache_page(vma, addr, pte_pfn(pte)); + anon_exclusive = folio_test_anon(folio) && + PageAnonExclusive(page); + if (anon_exclusive) { + pte = ptep_clear_flush(vma, addr, ptep); + + if (folio_try_share_anon_rmap_pte(folio, page)) { + set_pte_at(mm, addr, ptep, pte); + if (fault_folio != folio) + folio_unlock(folio); + folio_put(folio); + 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(folio); + + /* 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 the folio refcount. The folio won't be freed, as + * we took a reference just above. + */ + folio_remove_rmap_pte(folio, page, vma); + folio_put(folio); + + if (pte_present(pte)) + unmapped++; + } else { + folio_put(folio); + 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) +{ + struct folio *folio = page_folio(page); + + /* + * One extra ref because caller holds an extra reference, either from + * folio_isolate_lru() for a regular folio, or migrate_vma_collect() for + * a device folio. + */ + int extra = 1 + (page == fault_page); + + /* Page from ZONE_DEVICE have one extra reference */ + if (folio_is_zone_device(folio)) + extra++; + + /* For file back page */ + if (folio_mapping(folio)) + extra += 1 + folio_has_private(folio); + + if ((folio_ref_count(folio) - extra) > folio_mapcount(folio)) + 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) +{ + struct folio *fault_folio = fault_page ? + page_folio(fault_page) : NULL; + unsigned long i, restore = 0; + bool allow_drain = true; + unsigned long unmapped = 0; + + lru_add_drain(); + + for (i = 0; i < npages; ) { + struct page *page = migrate_pfn_to_page(src_pfns[i]); + struct folio *folio; + unsigned int nr = 1; + + if (!page) { + if (src_pfns[i] & MIGRATE_PFN_MIGRATE) + unmapped++; + goto next; + } + + folio = page_folio(page); + nr = folio_nr_pages(folio); + + if (nr > 1) + src_pfns[i] |= MIGRATE_PFN_COMPOUND; + + + /* ZONE_DEVICE folios are not on LRU */ + if (!folio_is_zone_device(folio)) { + if (!folio_test_lru(folio) && allow_drain) { + /* Drain CPU's lru cache */ + lru_add_drain_all(); + allow_drain = false; + } + + if (!folio_isolate_lru(folio)) { + src_pfns[i] &= ~MIGRATE_PFN_MIGRATE; + restore++; + goto next; + } + + /* Drop the reference we took in collect */ + folio_put(folio); + } + + if (folio_mapped(folio)) + try_to_migrate(folio, 0); + + if (folio_mapped(folio) || + !migrate_vma_check_page(page, fault_page)) { + if (!folio_is_zone_device(folio)) { + folio_get(folio); + folio_putback_lru(folio); + } + + src_pfns[i] &= ~MIGRATE_PFN_MIGRATE; + restore++; + goto next; + } + + unmapped++; +next: + i += nr; + } + + 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, 0); + + src_pfns[i] = 0; + if (fault_folio != folio) + 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; + if (args->fault_page && !PageLocked(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); + +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION +/** + * migrate_vma_insert_huge_pmd_page: Insert a huge folio into @migrate->vma->vm_mm + * at @addr. folio is already allocated as a part of the migration process with + * large page. + * + * @page needs to be initialized and setup after it's allocated. The code bits + * here follow closely the code in __do_huge_pmd_anonymous_page(). This API does + * not support THP zero pages. + * + * @migrate: migrate_vma arguments + * @addr: address where the folio will be inserted + * @page: page to be inserted at @addr + * @src: src pfn which is being migrated + * @pmdp: pointer to the pmd + */ +static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate, + unsigned long addr, + struct page *page, + unsigned long *src, + pmd_t *pmdp) +{ + struct vm_area_struct *vma = migrate->vma; + gfp_t gfp = vma_thp_gfp_mask(vma); + struct folio *folio = page_folio(page); + int ret; + vm_fault_t csa_ret; + spinlock_t *ptl; + pgtable_t pgtable; + pmd_t entry; + bool flush = false; + unsigned long i; + + VM_WARN_ON_FOLIO(!folio, folio); + VM_WARN_ON_ONCE(!pmd_none(*pmdp) && !is_huge_zero_pmd(*pmdp)); + + if (!thp_vma_suitable_order(vma, addr, HPAGE_PMD_ORDER)) + return -EINVAL; + + ret = anon_vma_prepare(vma); + if (ret) + return ret; + + folio_set_order(folio, HPAGE_PMD_ORDER); + folio_set_large_rmappable(folio); + + if (mem_cgroup_charge(folio, migrate->vma->vm_mm, gfp)) { + count_vm_event(THP_FAULT_FALLBACK); + count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE); + ret = -ENOMEM; + goto abort; + } + + __folio_mark_uptodate(folio); + + pgtable = pte_alloc_one(vma->vm_mm); + if (unlikely(!pgtable)) + goto abort; + + if (folio_is_device_private(folio)) { + 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_pmd(swp_entry); + } else { + if (folio_is_zone_device(folio) && + !folio_is_device_coherent(folio)) { + goto abort; + } + entry = folio_mk_pmd(folio, vma->vm_page_prot); + if (vma->vm_flags & VM_WRITE) + entry = pmd_mkwrite(pmd_mkdirty(entry), vma); + } + + ptl = pmd_lock(vma->vm_mm, pmdp); + csa_ret = check_stable_address_space(vma->vm_mm); + if (csa_ret) + goto abort; + + /* + * Check for userfaultfd but do not deliver the fault. Instead, + * just back off. + */ + if (userfaultfd_missing(vma)) + goto unlock_abort; + + if (!pmd_none(*pmdp)) { + if (!is_huge_zero_pmd(*pmdp)) + goto unlock_abort; + flush = true; + } else if (!pmd_none(*pmdp)) + goto unlock_abort; + + add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR); + folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE); + if (!folio_is_zone_device(folio)) + folio_add_lru_vma(folio, vma); + folio_get(folio); + + if (flush) { + pte_free(vma->vm_mm, pgtable); + flush_cache_page(vma, addr, addr + HPAGE_PMD_SIZE); + pmdp_invalidate(vma, addr, pmdp); + } else { + pgtable_trans_huge_deposit(vma->vm_mm, pmdp, pgtable); + mm_inc_nr_ptes(vma->vm_mm); + } + set_pmd_at(vma->vm_mm, addr, pmdp, entry); + update_mmu_cache_pmd(vma, addr, pmdp); + + spin_unlock(ptl); + + count_vm_event(THP_FAULT_ALLOC); + count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_ALLOC); + count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC); + + return 0; + +unlock_abort: + spin_unlock(ptl); +abort: + for (i = 0; i < HPAGE_PMD_NR; i++) + src[i] &= ~MIGRATE_PFN_MIGRATE; + return 0; +} + +static int migrate_vma_split_unmapped_folio(struct migrate_vma *migrate, + unsigned long idx, unsigned long addr, + struct folio *folio) +{ + unsigned long i; + unsigned long pfn; + unsigned long flags; + int ret = 0; + + folio_get(folio); + split_huge_pmd_address(migrate->vma, addr, true); + ret = folio_split_unmapped(folio, 0); + if (ret) + return ret; + migrate->src[idx] &= ~MIGRATE_PFN_COMPOUND; + flags = migrate->src[idx] & ((1UL << MIGRATE_PFN_SHIFT) - 1); + pfn = migrate->src[idx] >> MIGRATE_PFN_SHIFT; + for (i = 1; i < HPAGE_PMD_NR; i++) + migrate->src[i+idx] = migrate_pfn(pfn + i) | flags; + return ret; +} +#else /* !CONFIG_ARCH_ENABLE_THP_MIGRATION */ +static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate, + unsigned long addr, + struct page *page, + unsigned long *src, + pmd_t *pmdp) +{ + return 0; +} + +static int migrate_vma_split_unmapped_folio(struct migrate_vma *migrate, + unsigned long idx, unsigned long addr, + struct folio *folio) +{ + return 0; +} +#endif + +static unsigned long migrate_vma_nr_pages(unsigned long *src) +{ + unsigned long nr = 1; +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION + if (*src & MIGRATE_PFN_COMPOUND) + nr = HPAGE_PMD_NR; +#else + if (*src & MIGRATE_PFN_COMPOUND) + VM_WARN_ON_ONCE(true); +#endif + return nr; +} + +/* + * 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, + unsigned long *dst, + unsigned long *src) +{ + struct page *page = migrate_pfn_to_page(*dst); + struct folio *folio = page_folio(page); + 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 (thp_migration_supported() && (*dst & MIGRATE_PFN_COMPOUND)) { + int ret = migrate_vma_insert_huge_pmd_page(migrate, addr, page, + src, pmdp); + if (ret) + goto abort; + return; + } + + if (!pmd_none(*pmdp)) { + if (pmd_trans_huge(*pmdp)) { + if (!is_huge_zero_pmd(*pmdp)) + goto abort; + split_huge_pmd(vma, pmdp, addr); + } else if (pmd_leaf(*pmdp)) + goto abort; + } + + if (pte_alloc(mm, pmdp)) + goto abort; + if (unlikely(anon_vma_prepare(vma))) + goto abort; + if (mem_cgroup_charge(folio, vma->vm_mm, GFP_KERNEL)) + goto abort; + + /* + * The memory barrier inside __folio_mark_uptodate makes sure that + * preceding stores to the folio contents become visible before + * the set_pte_at() write. + */ + __folio_mark_uptodate(folio); + + if (folio_is_device_private(folio)) { + 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 (folio_is_zone_device(folio) && + !folio_is_device_coherent(folio)) { + 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); + folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE); + if (!folio_is_zone_device(folio)) + folio_add_lru_vma(folio, vma); + folio_get(folio); + + if (flush) { + flush_cache_page(vma, addr, pte_pfn(orig_pte)); + ptep_clear_flush(vma, addr, ptep); + } + 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, j; + bool notified = false; + unsigned long addr; + + for (i = 0; i < npages; ) { + struct page *newpage = migrate_pfn_to_page(dst_pfns[i]); + struct page *page = migrate_pfn_to_page(src_pfns[i]); + struct address_space *mapping; + struct folio *newfolio, *folio; + int r, extra_cnt = 0; + unsigned long nr = 1; + + if (!newpage) { + src_pfns[i] &= ~MIGRATE_PFN_MIGRATE; + goto next; + } + + if (!page) { + unsigned long addr; + + if (!(src_pfns[i] & MIGRATE_PFN_MIGRATE)) + goto next; + + /* + * The only time there is no vma is when called from + * migrate_device_coherent_folio(). 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); + } + + if ((src_pfns[i] & MIGRATE_PFN_COMPOUND) && + (!(dst_pfns[i] & MIGRATE_PFN_COMPOUND))) { + nr = migrate_vma_nr_pages(&src_pfns[i]); + src_pfns[i] &= ~MIGRATE_PFN_COMPOUND; + } else { + nr = 1; + } + + for (j = 0; j < nr && i + j < npages; j++) { + src_pfns[i+j] |= MIGRATE_PFN_MIGRATE; + migrate_vma_insert_page(migrate, + addr + j * PAGE_SIZE, + &dst_pfns[i+j], &src_pfns[i+j]); + } + goto next; + } + + newfolio = page_folio(newpage); + folio = page_folio(page); + mapping = folio_mapping(folio); + + /* + * If THP migration is enabled, check if both src and dst + * can migrate large pages + */ + if (thp_migration_supported()) { + if ((src_pfns[i] & MIGRATE_PFN_MIGRATE) && + (src_pfns[i] & MIGRATE_PFN_COMPOUND) && + !(dst_pfns[i] & MIGRATE_PFN_COMPOUND)) { + + if (!migrate) { + src_pfns[i] &= ~(MIGRATE_PFN_MIGRATE | + MIGRATE_PFN_COMPOUND); + goto next; + } + nr = 1 << folio_order(folio); + addr = migrate->start + i * PAGE_SIZE; + if (migrate_vma_split_unmapped_folio(migrate, i, addr, folio)) { + src_pfns[i] &= ~(MIGRATE_PFN_MIGRATE | + MIGRATE_PFN_COMPOUND); + goto next; + } + } else if ((src_pfns[i] & MIGRATE_PFN_MIGRATE) && + (dst_pfns[i] & MIGRATE_PFN_COMPOUND) && + !(src_pfns[i] & MIGRATE_PFN_COMPOUND)) { + src_pfns[i] &= ~MIGRATE_PFN_MIGRATE; + } + } + + + if (folio_is_device_private(newfolio) || + folio_is_device_coherent(newfolio)) { + if (mapping) { + /* + * 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; + goto next; + } + } + } else if (folio_is_zone_device(newfolio)) { + /* + * Other types of ZONE_DEVICE page are not supported. + */ + src_pfns[i] &= ~MIGRATE_PFN_MIGRATE; + goto next; + } + + BUG_ON(folio_test_writeback(folio)); + + if (migrate && migrate->fault_page == page) + extra_cnt = 1; + for (j = 0; j < nr && i + j < npages; j++) { + folio = page_folio(migrate_pfn_to_page(src_pfns[i+j])); + newfolio = page_folio(migrate_pfn_to_page(dst_pfns[i+j])); + + r = folio_migrate_mapping(mapping, newfolio, folio, extra_cnt); + if (r) + src_pfns[i+j] &= ~MIGRATE_PFN_MIGRATE; + else + folio_migrate_flags(newfolio, folio); + } +next: + i += nr; + } + + 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); + +static void __migrate_device_finalize(unsigned long *src_pfns, + unsigned long *dst_pfns, + unsigned long npages, + struct page *fault_page) +{ + struct folio *fault_folio = fault_page ? + page_folio(fault_page) : NULL; + unsigned long i; + + for (i = 0; i < npages; i++) { + struct folio *dst = NULL, *src = NULL; + struct page *newpage = migrate_pfn_to_page(dst_pfns[i]); + struct page *page = migrate_pfn_to_page(src_pfns[i]); + + if (newpage) + dst = page_folio(newpage); + + if (!page) { + if (dst) { + WARN_ON_ONCE(fault_folio == dst); + folio_unlock(dst); + folio_put(dst); + } + continue; + } + + src = page_folio(page); + + if (!(src_pfns[i] & MIGRATE_PFN_MIGRATE) || !dst) { + if (dst) { + WARN_ON_ONCE(fault_folio == dst); + folio_unlock(dst); + folio_put(dst); + } + dst = src; + } + + if (!folio_is_zone_device(dst)) + folio_add_lru(dst); + remove_migration_ptes(src, dst, 0); + if (fault_folio != src) + folio_unlock(src); + folio_put(src); + + if (dst != src) { + WARN_ON_ONCE(fault_folio == dst); + folio_unlock(dst); + folio_put(dst); + } + } +} + +/* + * 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) +{ + return __migrate_device_finalize(src_pfns, dst_pfns, npages, NULL); +} +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, + migrate->fault_page); +} +EXPORT_SYMBOL(migrate_vma_finalize); + +static unsigned long migrate_device_pfn_lock(unsigned long pfn) +{ + struct folio *folio; + + folio = folio_get_nontail_page(pfn_to_page(pfn)); + if (!folio) + return 0; + + if (!folio_trylock(folio)) { + folio_put(folio); + return 0; + } + + return migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE; +} + +/** + * 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, j, pfn; + + for (pfn = start, i = 0; i < npages; pfn++, i++) { + struct page *page = pfn_to_page(pfn); + struct folio *folio = page_folio(page); + unsigned int nr = 1; + + src_pfns[i] = migrate_device_pfn_lock(pfn); + nr = folio_nr_pages(folio); + if (nr > 1) { + src_pfns[i] |= MIGRATE_PFN_COMPOUND; + for (j = 1; j < nr; j++) + src_pfns[i+j] = 0; + i += j - 1; + pfn += j - 1; + } + } + + migrate_device_unmap(src_pfns, npages, NULL); + + return 0; +} +EXPORT_SYMBOL(migrate_device_range); + +/** + * migrate_device_pfns() - migrate device private pfns to normal memory. + * @src_pfns: pre-popluated array of source device private pfns to migrate. + * @npages: number of pages to migrate. + * + * Similar to migrate_device_range() but supports non-contiguous pre-popluated + * array of device pages to migrate. + */ +int migrate_device_pfns(unsigned long *src_pfns, unsigned long npages) +{ + unsigned long i, j; + + for (i = 0; i < npages; i++) { + struct page *page = pfn_to_page(src_pfns[i]); + struct folio *folio = page_folio(page); + unsigned int nr = 1; + + src_pfns[i] = migrate_device_pfn_lock(src_pfns[i]); + nr = folio_nr_pages(folio); + if (nr > 1) { + src_pfns[i] |= MIGRATE_PFN_COMPOUND; + for (j = 1; j < nr; j++) + src_pfns[i+j] = 0; + i += j - 1; + } + } + + migrate_device_unmap(src_pfns, npages, NULL); + + return 0; +} +EXPORT_SYMBOL(migrate_device_pfns); + +/* + * Migrate a device coherent folio back to normal memory. The caller should have + * a reference on folio which will be copied to the new folio if migration is + * successful or dropped on failure. + */ +int migrate_device_coherent_folio(struct folio *folio) +{ + unsigned long src_pfn, dst_pfn = 0; + struct folio *dfolio; + + WARN_ON_ONCE(folio_test_large(folio)); + + folio_lock(folio); + src_pfn = migrate_pfn(folio_pfn(folio)) | MIGRATE_PFN_MIGRATE; + + /* + * We don't have a VMA and don't need to walk the page tables to find + * the source folio. So call migrate_vma_unmap() directly to unmap the + * folio 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; + + dfolio = folio_alloc(GFP_USER | __GFP_NOWARN, 0); + if (dfolio) { + folio_lock(dfolio); + dst_pfn = migrate_pfn(folio_pfn(dfolio)); + } + + migrate_device_pages(&src_pfn, &dst_pfn, 1); + if (src_pfn & MIGRATE_PFN_MIGRATE) + folio_copy(dfolio, folio); + migrate_device_finalize(&src_pfn, &dst_pfn, 1); + + if (src_pfn & MIGRATE_PFN_MIGRATE) + return 0; + return -EBUSY; +} |