1 files changed, 492 insertions, 0 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index 71de36cfb673..991e8886093f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -428,6 +428,14 @@ int migrate_page_move_mapping(struct address_space *mapping,
 	int expected_count = 1 + extra_count;
 	void **pslot;
 
+	/*
+	 * ZONE_DEVICE pages have 1 refcount always held by their device
+	 *
+	 * Note that DAX memory will never reach that point as it does not have
+	 * the MEMORY_DEVICE_ALLOW_MIGRATE flag set (see memory_hotplug.h).
+	 */
+	expected_count += is_zone_device_page(page);
+
 	if (!mapping) {
 		/* Anonymous page without mapping */
 		if (page_count(page) != expected_count)
@@ -2106,3 +2114,487 @@ out_unlock:
 #endif /* CONFIG_NUMA_BALANCING */
 
 #endif /* CONFIG_NUMA */
+
+
+struct migrate_vma {
+	struct vm_area_struct	*vma;
+	unsigned long		*dst;
+	unsigned long		*src;
+	unsigned long		cpages;
+	unsigned long		npages;
+	unsigned long		start;
+	unsigned long		end;
+};
+
+static int migrate_vma_collect_hole(unsigned long start,
+				    unsigned long end,
+				    struct mm_walk *walk)
+{
+	struct migrate_vma *migrate = walk->private;
+	unsigned long addr;
+
+	for (addr = start & PAGE_MASK; addr < end; addr += PAGE_SIZE) {
+		migrate->dst[migrate->npages] = 0;
+		migrate->src[migrate->npages++] = 0;
+	}
+
+	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;
+	spinlock_t *ptl;
+	pte_t *ptep;
+
+again:
+	if (pmd_none(*pmdp))
+		return migrate_vma_collect_hole(start, end, 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_hole(start, end,
+								walk);
+		} else {
+			int ret;
+
+			get_page(page);
+			spin_unlock(ptl);
+			if (unlikely(!trylock_page(page)))
+				return migrate_vma_collect_hole(start, end,
+								walk);
+			ret = split_huge_page(page);
+			unlock_page(page);
+			put_page(page);
+			if (ret || pmd_none(*pmdp))
+				return migrate_vma_collect_hole(start, end,
+								walk);
+		}
+	}
+
+	if (unlikely(pmd_bad(*pmdp)))
+		return migrate_vma_collect_hole(start, end, walk);
+
+	ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
+	for (; addr < end; addr += PAGE_SIZE, ptep++) {
+		unsigned long mpfn, pfn;
+		struct page *page;
+		pte_t pte;
+
+		pte = *ptep;
+		pfn = pte_pfn(pte);
+
+		if (!pte_present(pte)) {
+			mpfn = pfn = 0;
+			goto next;
+		}
+
+		/* FIXME support THP */
+		page = vm_normal_page(migrate->vma, addr, pte);
+		if (!page || !page->mapping || PageTransCompound(page)) {
+			mpfn = pfn = 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);
+		migrate->cpages++;
+		mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
+		mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
+
+next:
+		migrate->src[migrate->npages++] = mpfn;
+	}
+	pte_unmap_unlock(ptep - 1, ptl);
+
+	return 0;
+}
+
+/*
+ * 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 mm_walk mm_walk;
+
+	mm_walk.pmd_entry = migrate_vma_collect_pmd;
+	mm_walk.pte_entry = NULL;
+	mm_walk.pte_hole = migrate_vma_collect_hole;
+	mm_walk.hugetlb_entry = NULL;
+	mm_walk.test_walk = NULL;
+	mm_walk.vma = migrate->vma;
+	mm_walk.mm = migrate->vma->vm_mm;
+	mm_walk.private = migrate;
+
+	walk_page_range(migrate->start, migrate->end, &mm_walk);
+
+	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
+ * migrate_page_move_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;
+
+	if ((page_count(page) - extra) > page_mapcount(page))
+		return false;
+
+	return true;
+}
+
+/*
+ * migrate_vma_prepare() - lock pages and isolate them from the lru
+ * @migrate: migrate struct containing all migration information
+ *
+ * This locks pages that have been collected by migrate_vma_collect(). Once each
+ * page is locked it is isolated from the lru (for non-device pages). Finally,
+ * the ref taken by migrate_vma_collect() is dropped, as locked pages cannot be
+ * migrated by concurrent kernel threads.
+ */
+static void migrate_vma_prepare(struct migrate_vma *migrate)
+{
+	const unsigned long npages = migrate->npages;
+	bool allow_drain = true;
+	unsigned long i;
+
+	lru_add_drain();
+
+	for (i = 0; (i < npages) && migrate->cpages; i++) {
+		struct page *page = migrate_pfn_to_page(migrate->src[i]);
+
+		if (!page)
+			continue;
+
+		/*
+		 * Because we are migrating several pages there can be
+		 * a deadlock between 2 concurrent migration where each
+		 * are waiting on each other page lock.
+		 *
+		 * Make migrate_vma() a best effort thing and backoff
+		 * for any page we can not lock right away.
+		 */
+		if (!trylock_page(page)) {
+			migrate->src[i] = 0;
+			migrate->cpages--;
+			put_page(page);
+			continue;
+		}
+		migrate->src[i] |= MIGRATE_PFN_LOCKED;
+
+		if (!PageLRU(page) && allow_drain) {
+			/* Drain CPU's pagevec */
+			lru_add_drain_all();
+			allow_drain = false;
+		}
+
+		if (isolate_lru_page(page)) {
+			migrate->src[i] = 0;
+			unlock_page(page);
+			migrate->cpages--;
+			put_page(page);
+			continue;
+		}
+
+		if (!migrate_vma_check_page(page)) {
+			migrate->src[i] = 0;
+			unlock_page(page);
+			migrate->cpages--;
+
+			putback_lru_page(page);
+		}
+	}
+}
+
+/*
+ * migrate_vma_unmap() - replace page mapping with special migration pte entry
+ * @migrate: migrate struct containing all migration information
+ *
+ * Replace page mapping (CPU page table pte) with a special migration pte entry
+ * and check again 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)
+{
+	int flags = TTU_MIGRATION | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
+	const unsigned long npages = migrate->npages;
+	const unsigned long start = migrate->start;
+	unsigned long addr, i, restore = 0;
+
+	for (i = 0; i < npages; i++) {
+		struct page *page = migrate_pfn_to_page(migrate->src[i]);
+
+		if (!page || !(migrate->src[i] & MIGRATE_PFN_MIGRATE))
+			continue;
+
+		try_to_unmap(page, flags);
+		if (page_mapped(page) || !migrate_vma_check_page(page)) {
+			migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
+			migrate->cpages--;
+			restore++;
+		}
+	}
+
+	for (addr = start, i = 0; i < npages && restore; addr += PAGE_SIZE, i++) {
+		struct page *page = migrate_pfn_to_page(migrate->src[i]);
+
+		if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE))
+			continue;
+
+		remove_migration_ptes(page, page, false);
+
+		migrate->src[i] = 0;
+		unlock_page(page);
+		restore--;
+
+		putback_lru_page(page);
+	}
+}
+
+/*
+ * 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.
+ */
+static void migrate_vma_pages(struct migrate_vma *migrate)
+{
+	const unsigned long npages = migrate->npages;
+	const unsigned long start = migrate->start;
+	unsigned long addr, i;
+
+	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 (!page || !newpage)
+			continue;
+		if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE))
+			continue;
+
+		mapping = page_mapping(page);
+
+		r = migrate_page(mapping, newpage, page, MIGRATE_SYNC_NO_COPY);
+		if (r != MIGRATEPAGE_SUCCESS)
+			migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
+	}
+}
+
+/*
+ * 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.
+ */
+static void migrate_vma_finalize(struct migrate_vma *migrate)
+{
+	const unsigned long npages = migrate->npages;
+	unsigned long i;
+
+	for (i = 0; i < npages; i++) {
+		struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
+		struct page *page = migrate_pfn_to_page(migrate->src[i]);
+
+		if (!page)
+			continue;
+		if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE) || !newpage) {
+			if (newpage) {
+				unlock_page(newpage);
+				put_page(newpage);
+			}
+			newpage = page;
+		}
+
+		remove_migration_ptes(page, newpage, false);
+		unlock_page(page);
+		migrate->cpages--;
+
+		putback_lru_page(page);
+
+		if (newpage != page) {
+			unlock_page(newpage);
+			putback_lru_page(newpage);
+		}
+	}
+}
+
+/*
+ * migrate_vma() - migrate a range of memory inside vma
+ *
+ * @ops: migration callback for allocating destination memory and copying
+ * @vma: virtual memory area containing the range to be migrated
+ * @start: start address of the range to migrate (inclusive)
+ * @end: end address of the range to migrate (exclusive)
+ * @src: array of hmm_pfn_t containing source pfns
+ * @dst: array of hmm_pfn_t containing destination pfns
+ * @private: pointer passed back to each of the callback
+ * Returns: 0 on success, error code otherwise
+ *
+ * This function tries to migrate a range of memory virtual address range, using
+ * callbacks to allocate and copy memory from source to destination. First it
+ * collects all the pages backing each virtual address in the range, saving this
+ * inside the src array. Then it locks those pages and unmaps them. Once the pages
+ * are locked and unmapped, it checks 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. It then restores any pages that are
+ * pinned, by remapping and unlocking those pages.
+ *
+ * At this point it calls the alloc_and_copy() callback. For documentation on
+ * what is expected from that callback, see struct migrate_vma_ops comments in
+ * include/linux/migrate.h
+ *
+ * After the alloc_and_copy() callback, this function goes 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 the function tries 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.
+ *
+ * It then calls the finalize_and_map() callback. See comments for "struct
+ * migrate_vma_ops", in include/linux/migrate.h for details about
+ * finalize_and_map() behavior.
+ *
+ * After the finalize_and_map() callback, for successfully migrated pages, this
+ * function updates the CPU page table to point to new pages, otherwise it
+ * restores the CPU page table to point to the original source pages.
+ *
+ * Function returns 0 after the above steps, even if no pages were migrated
+ * (The function only returns an error if any of the arguments are invalid.)
+ *
+ * Both src and dst array must be big enough for (end - start) >> PAGE_SHIFT
+ * unsigned long entries.
+ */
+int migrate_vma(const struct migrate_vma_ops *ops,
+		struct vm_area_struct *vma,
+		unsigned long start,
+		unsigned long end,
+		unsigned long *src,
+		unsigned long *dst,
+		void *private)
+{
+	struct migrate_vma migrate;
+
+	/* Sanity check the arguments */
+	start &= PAGE_MASK;
+	end &= PAGE_MASK;
+	if (!vma || is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL))
+		return -EINVAL;
+	if (start < vma->vm_start || start >= vma->vm_end)
+		return -EINVAL;
+	if (end <= vma->vm_start || end > vma->vm_end)
+		return -EINVAL;
+	if (!ops || !src || !dst || start >= end)
+		return -EINVAL;
+
+	memset(src, 0, sizeof(*src) * ((end - start) >> PAGE_SHIFT));
+	migrate.src = src;
+	migrate.dst = dst;
+	migrate.start = start;
+	migrate.npages = 0;
+	migrate.cpages = 0;
+	migrate.end = end;
+	migrate.vma = vma;
+
+	/* Collect, and try to unmap source pages */
+	migrate_vma_collect(&migrate);
+	if (!migrate.cpages)
+		return 0;
+
+	/* Lock and isolate page */
+	migrate_vma_prepare(&migrate);
+	if (!migrate.cpages)
+		return 0;
+
+	/* Unmap pages */
+	migrate_vma_unmap(&migrate);
+	if (!migrate.cpages)
+		return 0;
+
+	/*
+	 * 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 callback.
+	 *
+	 * Note that migration can fail in migrate_vma_struct_page() for each
+	 * individual page.
+	 */
+	ops->alloc_and_copy(vma, src, dst, start, end, private);
+
+	/* This does the real migration of struct page */
+	migrate_vma_pages(&migrate);
+
+	ops->finalize_and_map(vma, src, dst, start, end, private);
+
+	/* Unlock and remap pages */
+	migrate_vma_finalize(&migrate);
+
+	return 0;
+}
+EXPORT_SYMBOL(migrate_vma);