// SPDX-License-Identifier: GPL-2.0 /* * Device Memory Migration functionality. * * Originally written by Jérôme Glisse. */ #include #include #include #include #include #include #include #include #include #include #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); if (pmd_trans_unstable(pmdp)) return migrate_vma_collect_skip(start, end, walk); } 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); if (pmd_none(*pmdp)) return migrate_vma_collect_hole(start, end, -1, walk); } } if (unlikely(pmd_bad(*pmdp))) return migrate_vma_collect_skip(start, end, walk); ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); 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; 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 { if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) goto next; pfn = pte_pfn(pte); if (is_zero_pfn(pfn)) { mpfn = MIGRATE_PFN_MIGRATE; migrate->cpages++; goto next; } page = vm_normal_page(migrate->vma, addr, pte); 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); /* * Optimize for the common case where page is only mapped once * in one process. If we can lock the page, then we can safely * set up a special migration page table entry now. */ if (trylock_page(page)) { pte_t swp_pte; migrate->cpages++; ptep_get_and_clear(mm, addr, ptep); /* Setup special migration page table entry */ if (mpfn & MIGRATE_PFN_WRITE) entry = make_writable_migration_entry( page_to_pfn(page)); else entry = make_readable_migration_entry( page_to_pfn(page)); 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; } arch_leave_lazy_mmu_mode(); pte_unmap_unlock(ptep - 1, ptl); /* Only flush the TLB if we actually modified any entries */ if (unmapped) flush_tlb_range(walk->vma, start, end); return 0; } static const struct mm_walk_ops migrate_vma_walk_ops = { .pmd_entry = migrate_vma_collect_pmd, .pte_hole = migrate_vma_collect_hole, }; /* * 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, 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) { /* * 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; /* * 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; } /* * 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) { const unsigned long npages = migrate->npages; unsigned long i, restore = 0; bool allow_drain = true; lru_add_drain(); for (i = 0; i < npages; i++) { struct page *page = migrate_pfn_to_page(migrate->src[i]); struct folio *folio; if (!page) continue; /* ZONE_DEVICE pages are not on LRU */ if (!is_zone_device_page(page)) { if (!PageLRU(page) && allow_drain) { /* Drain CPU's pagevec */ lru_add_drain_all(); allow_drain = false; } if (isolate_lru_page(page)) { migrate->src[i] &= ~MIGRATE_PFN_MIGRATE; migrate->cpages--; 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)) { if (!is_zone_device_page(page)) { get_page(page); putback_lru_page(page); } migrate->src[i] &= ~MIGRATE_PFN_MIGRATE; migrate->cpages--; restore++; continue; } } for (i = 0; i < npages && restore; i++) { struct page *page = migrate_pfn_to_page(migrate->src[i]); struct folio *folio; if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE)) continue; folio = page_folio(page); remove_migration_ptes(folio, folio, false); migrate->src[i] = 0; folio_unlock(folio); folio_put(folio); restore--; } } /** * 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; 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 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; /* 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; /* * Use pte_alloc() instead of pte_alloc_map(). We can't run * pte_offset_map() on pmds where a huge pmd might be created * from a different thread. * * pte_alloc_map() is safe to use under mmap_write_lock(mm) or when * parallel threads are excluded by other means. * * Here we only have mmap_read_lock(mm). */ if (pte_alloc(mm, pmdp)) goto abort; /* See the comment in pte_alloc_one_map() */ if (unlikely(pmd_trans_unstable(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 { /* * For now we only support migrating to un-addressable device * memory. */ if (is_zone_device_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)); } ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); if (check_stable_address_space(mm)) goto unlock_abort; if (pte_present(*ptep)) { unsigned long pfn = pte_pfn(*ptep); if (!is_zero_pfn(pfn)) goto unlock_abort; flush = true; } else if (!pte_none(*ptep)) 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, false); 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(*ptep)); ptep_clear_flush_notify(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; } /** * 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) { const unsigned long npages = migrate->npages; const unsigned long start = migrate->start; struct mmu_notifier_range range; unsigned long addr, i; bool notified = false; for (i = 0, addr = start; i < npages; addr += PAGE_SIZE, i++) { struct page *newpage = migrate_pfn_to_page(migrate->dst[i]); struct page *page = migrate_pfn_to_page(migrate->src[i]); struct address_space *mapping; int r; if (!newpage) { migrate->src[i] &= ~MIGRATE_PFN_MIGRATE; continue; } if (!page) { if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE)) continue; if (!notified) { notified = true; mmu_notifier_range_init_owner(&range, MMU_NOTIFY_MIGRATE, 0, migrate->vma, migrate->vma->vm_mm, addr, migrate->end, migrate->pgmap_owner); mmu_notifier_invalidate_range_start(&range); } migrate_vma_insert_page(migrate, addr, newpage, &migrate->src[i]); continue; } mapping = page_mapping(page); if (is_device_private_page(newpage)) { /* * For now only support private anonymous when migrating * to un-addressable device memory. */ if (mapping) { migrate->src[i] &= ~MIGRATE_PFN_MIGRATE; continue; } } else if (is_zone_device_page(newpage)) { /* * Other types of ZONE_DEVICE page are not supported. */ migrate->src[i] &= ~MIGRATE_PFN_MIGRATE; continue; } r = migrate_page(mapping, newpage, page, MIGRATE_SYNC_NO_COPY); if (r != MIGRATEPAGE_SUCCESS) migrate->src[i] &= ~MIGRATE_PFN_MIGRATE; } /* * No need to double call mmu_notifier->invalidate_range() callback as * the above ptep_clear_flush_notify() inside migrate_vma_insert_page() * did already call it. */ if (notified) mmu_notifier_invalidate_range_only_end(&range); } EXPORT_SYMBOL(migrate_vma_pages); /** * 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) { const unsigned long npages = migrate->npages; unsigned long i; for (i = 0; i < npages; i++) { struct folio *dst, *src; struct page *newpage = migrate_pfn_to_page(migrate->dst[i]); struct page *page = migrate_pfn_to_page(migrate->src[i]); if (!page) { if (newpage) { unlock_page(newpage); put_page(newpage); } continue; } if (!(migrate->src[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_vma_finalize);