diff options
Diffstat (limited to 'mm/migrate_device.c')
| -rw-r--r-- | mm/migrate_device.c | 773 |
1 files changed, 773 insertions, 0 deletions
diff --git a/mm/migrate_device.c b/mm/migrate_device.c new file mode 100644 index 000000000000..70c7dc05bbfc --- /dev/null +++ b/mm/migrate_device.c @@ -0,0 +1,773 @@ +// 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_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); + 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); |