5 files changed, 1058 insertions, 58 deletions

diff --git a/drivers/gpu/drm/ttm/Makefile b/drivers/gpu/drm/ttm/Makefile
index dad298127226..40d07a35293a 100644
--- a/drivers/gpu/drm/ttm/Makefile
+++ b/drivers/gpu/drm/ttm/Makefile
@@ -4,7 +4,7 @@
 
 ttm-y := ttm_tt.o ttm_bo.o ttm_bo_util.o ttm_bo_vm.o ttm_module.o \
 	ttm_execbuf_util.o ttm_range_manager.o ttm_resource.o ttm_pool.o \
-	ttm_device.o ttm_sys_manager.o
+	ttm_device.o ttm_sys_manager.o ttm_backup.o
 ttm-$(CONFIG_AGP) += ttm_agp_backend.o
 
 obj-$(CONFIG_DRM_TTM) += ttm.o
diff --git a/drivers/gpu/drm/ttm/ttm_backup.c b/drivers/gpu/drm/ttm/ttm_backup.c
new file mode 100644
index 000000000000..93c007f18855
--- /dev/null
+++ b/drivers/gpu/drm/ttm/ttm_backup.c
@@ -0,0 +1,207 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright © 2024 Intel Corporation
+ */
+
+#include <drm/ttm/ttm_backup.h>
+#include <linux/page-flags.h>
+#include <linux/swap.h>
+
+/*
+ * Casting from randomized struct file * to struct ttm_backup * is fine since
+ * struct ttm_backup is never defined nor dereferenced.
+ */
+static struct file *ttm_backup_to_file(struct ttm_backup *backup)
+{
+	return (void *)backup;
+}
+
+static struct ttm_backup *ttm_file_to_backup(struct file *file)
+{
+	return (void *)file;
+}
+
+/*
+ * Need to map shmem indices to handle since a handle value
+ * of 0 means error, following the swp_entry_t convention.
+ */
+static unsigned long ttm_backup_shmem_idx_to_handle(pgoff_t idx)
+{
+	return (unsigned long)idx + 1;
+}
+
+static pgoff_t ttm_backup_handle_to_shmem_idx(pgoff_t handle)
+{
+	return handle - 1;
+}
+
+/**
+ * ttm_backup_drop() - release memory associated with a handle
+ * @backup: The struct backup pointer used to obtain the handle
+ * @handle: The handle obtained from the @backup_page function.
+ */
+void ttm_backup_drop(struct ttm_backup *backup, pgoff_t handle)
+{
+	loff_t start = ttm_backup_handle_to_shmem_idx(handle);
+
+	start <<= PAGE_SHIFT;
+	shmem_truncate_range(file_inode(ttm_backup_to_file(backup)), start,
+			     start + PAGE_SIZE - 1);
+}
+
+/**
+ * ttm_backup_copy_page() - Copy the contents of a previously backed
+ * up page
+ * @backup: The struct backup pointer used to back up the page.
+ * @dst: The struct page to copy into.
+ * @handle: The handle returned when the page was backed up.
+ * @intr: Try to perform waits interruptable or at least killable.
+ *
+ * Return: 0 on success, Negative error code on failure, notably
+ * -EINTR if @intr was set to true and a signal is pending.
+ */
+int ttm_backup_copy_page(struct ttm_backup *backup, struct page *dst,
+			 pgoff_t handle, bool intr)
+{
+	struct file *filp = ttm_backup_to_file(backup);
+	struct address_space *mapping = filp->f_mapping;
+	struct folio *from_folio;
+	pgoff_t idx = ttm_backup_handle_to_shmem_idx(handle);
+
+	from_folio = shmem_read_folio(mapping, idx);
+	if (IS_ERR(from_folio))
+		return PTR_ERR(from_folio);
+
+	copy_highpage(dst, folio_file_page(from_folio, idx));
+	folio_put(from_folio);
+
+	return 0;
+}
+
+/**
+ * ttm_backup_backup_page() - Backup a page
+ * @backup: The struct backup pointer to use.
+ * @page: The page to back up.
+ * @writeback: Whether to perform immediate writeback of the page.
+ * This may have performance implications.
+ * @idx: A unique integer for each page and each struct backup.
+ * This allows the backup implementation to avoid managing
+ * its address space separately.
+ * @page_gfp: The gfp value used when the page was allocated.
+ * This is used for accounting purposes.
+ * @alloc_gfp: The gfp to be used when allocating memory.
+ *
+ * Context: If called from reclaim context, the caller needs to
+ * assert that the shrinker gfp has __GFP_FS set, to avoid
+ * deadlocking on lock_page(). If @writeback is set to true and
+ * called from reclaim context, the caller also needs to assert
+ * that the shrinker gfp has __GFP_IO set, since without it,
+ * we're not allowed to start backup IO.
+ *
+ * Return: A handle on success. Negative error code on failure.
+ *
+ * Note: This function could be extended to back up a folio and
+ * implementations would then split the folio internally if needed.
+ * Drawback is that the caller would then have to keep track of
+ * the folio size- and usage.
+ */
+s64
+ttm_backup_backup_page(struct ttm_backup *backup, struct page *page,
+		       bool writeback, pgoff_t idx, gfp_t page_gfp,
+		       gfp_t alloc_gfp)
+{
+	struct file *filp = ttm_backup_to_file(backup);
+	struct address_space *mapping = filp->f_mapping;
+	unsigned long handle = 0;
+	struct folio *to_folio;
+	int ret;
+
+	to_folio = shmem_read_folio_gfp(mapping, idx, alloc_gfp);
+	if (IS_ERR(to_folio))
+		return PTR_ERR(to_folio);
+
+	folio_mark_accessed(to_folio);
+	folio_lock(to_folio);
+	folio_mark_dirty(to_folio);
+	copy_highpage(folio_file_page(to_folio, idx), page);
+	handle = ttm_backup_shmem_idx_to_handle(idx);
+
+	if (writeback && !folio_mapped(to_folio) &&
+	    folio_clear_dirty_for_io(to_folio)) {
+		struct writeback_control wbc = {
+			.sync_mode = WB_SYNC_NONE,
+			.nr_to_write = SWAP_CLUSTER_MAX,
+			.range_start = 0,
+			.range_end = LLONG_MAX,
+			.for_reclaim = 1,
+		};
+		folio_set_reclaim(to_folio);
+		ret = mapping->a_ops->writepage(folio_file_page(to_folio, idx), &wbc);
+		if (!folio_test_writeback(to_folio))
+			folio_clear_reclaim(to_folio);
+		/*
+		 * If writepage succeeds, it unlocks the folio.
+		 * writepage() errors are otherwise dropped, since writepage()
+		 * is only best effort here.
+		 */
+		if (ret)
+			folio_unlock(to_folio);
+	} else {
+		folio_unlock(to_folio);
+	}
+
+	folio_put(to_folio);
+
+	return handle;
+}
+
+/**
+ * ttm_backup_fini() - Free the struct backup resources after last use.
+ * @backup: Pointer to the struct backup whose resources to free.
+ *
+ * After a call to this function, it's illegal to use the @backup pointer.
+ */
+void ttm_backup_fini(struct ttm_backup *backup)
+{
+	fput(ttm_backup_to_file(backup));
+}
+
+/**
+ * ttm_backup_bytes_avail() - Report the approximate number of bytes of backup space
+ * left for backup.
+ *
+ * This function is intended also for driver use to indicate whether a
+ * backup attempt is meaningful.
+ *
+ * Return: An approximate size of backup space available.
+ */
+u64 ttm_backup_bytes_avail(void)
+{
+	/*
+	 * The idea behind backing up to shmem is that shmem objects may
+	 * eventually be swapped out. So no point swapping out if there
+	 * is no or low swap-space available. But the accuracy of this
+	 * number also depends on shmem actually swapping out backed-up
+	 * shmem objects without too much buffering.
+	 */
+	return (u64)get_nr_swap_pages() << PAGE_SHIFT;
+}
+EXPORT_SYMBOL_GPL(ttm_backup_bytes_avail);
+
+/**
+ * ttm_backup_shmem_create() - Create a shmem-based struct backup.
+ * @size: The maximum size (in bytes) to back up.
+ *
+ * Create a backup utilizing shmem objects.
+ *
+ * Return: A pointer to a struct ttm_backup on success,
+ * an error pointer on error.
+ */
+struct ttm_backup *ttm_backup_shmem_create(loff_t size)
+{
+	struct file *filp;
+
+	filp = shmem_file_setup("ttm shmem backup", size, 0);
+
+	return ttm_file_to_backup(filp);
+}
diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index 917096bd5f68..15cab9bda17f 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -28,7 +28,7 @@
 /*
  * Authors: Thomas Hellstrom <thellstrom-at-vmware-dot-com>
  */
-
+#include <linux/swap.h>
 #include <linux/vmalloc.h>
 
 #include <drm/ttm/ttm_bo.h>
@@ -769,12 +769,10 @@ error_destroy_tt:
 	return ret;
 }
 
-static bool ttm_lru_walk_trylock(struct ttm_lru_walk *walk,
+static bool ttm_lru_walk_trylock(struct ttm_operation_ctx *ctx,
 				 struct ttm_buffer_object *bo,
 				 bool *needs_unlock)
 {
-	struct ttm_operation_ctx *ctx = walk->ctx;
-
 	*needs_unlock = false;
 
 	if (dma_resv_trylock(bo->base.resv)) {
@@ -877,7 +875,7 @@ s64 ttm_lru_walk_for_evict(struct ttm_lru_walk *walk, struct ttm_device *bdev,
 		 * since if we do it the other way around, and the trylock fails,
 		 * we need to drop the lru lock to put the bo.
 		 */
-		if (ttm_lru_walk_trylock(walk, bo, &bo_needs_unlock))
+		if (ttm_lru_walk_trylock(walk->ctx, bo, &bo_needs_unlock))
 			bo_locked = true;
 		else if (!walk->ticket || walk->ctx->no_wait_gpu ||
 			 walk->trylock_only)
@@ -920,3 +918,242 @@ s64 ttm_lru_walk_for_evict(struct ttm_lru_walk *walk, struct ttm_device *bdev,
 
 	return progress;
 }
+EXPORT_SYMBOL(ttm_lru_walk_for_evict);
+
+static void ttm_bo_lru_cursor_cleanup_bo(struct ttm_bo_lru_cursor *curs)
+{
+	struct ttm_buffer_object *bo = curs->bo;
+
+	if (bo) {
+		if (curs->needs_unlock)
+			dma_resv_unlock(bo->base.resv);
+		ttm_bo_put(bo);
+		curs->bo = NULL;
+	}
+}
+
+/**
+ * ttm_bo_lru_cursor_fini() - Stop using a struct ttm_bo_lru_cursor
+ * and clean up any iteration it was used for.
+ * @curs: The cursor.
+ */
+void ttm_bo_lru_cursor_fini(struct ttm_bo_lru_cursor *curs)
+{
+	spinlock_t *lru_lock = &curs->res_curs.man->bdev->lru_lock;
+
+	ttm_bo_lru_cursor_cleanup_bo(curs);
+	spin_lock(lru_lock);
+	ttm_resource_cursor_fini(&curs->res_curs);
+	spin_unlock(lru_lock);
+}
+EXPORT_SYMBOL(ttm_bo_lru_cursor_fini);
+
+/**
+ * ttm_bo_lru_cursor_init() - Initialize a struct ttm_bo_lru_cursor
+ * @curs: The ttm_bo_lru_cursor to initialize.
+ * @man: The ttm resource_manager whose LRU lists to iterate over.
+ * @ctx: The ttm_operation_ctx to govern the locking.
+ *
+ * Initialize a struct ttm_bo_lru_cursor. Currently only trylocking
+ * or prelocked buffer objects are available as detailed by
+ * @ctx::resv and @ctx::allow_res_evict. Ticketlocking is not
+ * supported.
+ *
+ * Return: Pointer to @curs. The function does not fail.
+ */
+struct ttm_bo_lru_cursor *
+ttm_bo_lru_cursor_init(struct ttm_bo_lru_cursor *curs,
+		       struct ttm_resource_manager *man,
+		       struct ttm_operation_ctx *ctx)
+{
+	memset(curs, 0, sizeof(*curs));
+	ttm_resource_cursor_init(&curs->res_curs, man);
+	curs->ctx = ctx;
+
+	return curs;
+}
+EXPORT_SYMBOL(ttm_bo_lru_cursor_init);
+
+static struct ttm_buffer_object *
+ttm_bo_from_res_reserved(struct ttm_resource *res, struct ttm_bo_lru_cursor *curs)
+{
+	struct ttm_buffer_object *bo = res->bo;
+
+	if (!ttm_lru_walk_trylock(curs->ctx, bo, &curs->needs_unlock))
+		return NULL;
+
+	if (!ttm_bo_get_unless_zero(bo)) {
+		if (curs->needs_unlock)
+			dma_resv_unlock(bo->base.resv);
+		return NULL;
+	}
+
+	curs->bo = bo;
+	return bo;
+}
+
+/**
+ * ttm_bo_lru_cursor_next() - Continue iterating a manager's LRU lists
+ * to find and lock buffer object.
+ * @curs: The cursor initialized using ttm_bo_lru_cursor_init() and
+ * ttm_bo_lru_cursor_first().
+ *
+ * Return: A pointer to a locked and reference-counted buffer object,
+ * or NULL if none could be found and looping should be terminated.
+ */
+struct ttm_buffer_object *ttm_bo_lru_cursor_next(struct ttm_bo_lru_cursor *curs)
+{
+	spinlock_t *lru_lock = &curs->res_curs.man->bdev->lru_lock;
+	struct ttm_resource *res = NULL;
+	struct ttm_buffer_object *bo;
+
+	ttm_bo_lru_cursor_cleanup_bo(curs);
+
+	spin_lock(lru_lock);
+	for (;;) {
+		res = ttm_resource_manager_next(&curs->res_curs);
+		if (!res)
+			break;
+
+		bo = ttm_bo_from_res_reserved(res, curs);
+		if (bo)
+			break;
+	}
+
+	spin_unlock(lru_lock);
+	return res ? bo : NULL;
+}
+EXPORT_SYMBOL(ttm_bo_lru_cursor_next);
+
+/**
+ * ttm_bo_lru_cursor_first() - Start iterating a manager's LRU lists
+ * to find and lock buffer object.
+ * @curs: The cursor initialized using ttm_bo_lru_cursor_init().
+ *
+ * Return: A pointer to a locked and reference-counted buffer object,
+ * or NULL if none could be found and looping should be terminated.
+ */
+struct ttm_buffer_object *ttm_bo_lru_cursor_first(struct ttm_bo_lru_cursor *curs)
+{
+	spinlock_t *lru_lock = &curs->res_curs.man->bdev->lru_lock;
+	struct ttm_buffer_object *bo;
+	struct ttm_resource *res;
+
+	spin_lock(lru_lock);
+	res = ttm_resource_manager_first(&curs->res_curs);
+	if (!res) {
+		spin_unlock(lru_lock);
+		return NULL;
+	}
+
+	bo = ttm_bo_from_res_reserved(res, curs);
+	spin_unlock(lru_lock);
+
+	return bo ? bo : ttm_bo_lru_cursor_next(curs);
+}
+EXPORT_SYMBOL(ttm_bo_lru_cursor_first);
+
+/**
+ * ttm_bo_shrink() - Helper to shrink a ttm buffer object.
+ * @ctx: The struct ttm_operation_ctx used for the shrinking operation.
+ * @bo: The buffer object.
+ * @flags: Flags governing the shrinking behaviour.
+ *
+ * The function uses the ttm_tt_back_up functionality to back up or
+ * purge a struct ttm_tt. If the bo is not in system, it's first
+ * moved there.
+ *
+ * Return: The number of pages shrunken or purged, or
+ * negative error code on failure.
+ */
+long ttm_bo_shrink(struct ttm_operation_ctx *ctx, struct ttm_buffer_object *bo,
+		   const struct ttm_bo_shrink_flags flags)
+{
+	static const struct ttm_place sys_placement_flags = {
+		.fpfn = 0,
+		.lpfn = 0,
+		.mem_type = TTM_PL_SYSTEM,
+		.flags = 0,
+	};
+	static struct ttm_placement sys_placement = {
+		.num_placement = 1,
+		.placement = &sys_placement_flags,
+	};
+	struct ttm_tt *tt = bo->ttm;
+	long lret;
+
+	dma_resv_assert_held(bo->base.resv);
+
+	if (flags.allow_move && bo->resource->mem_type != TTM_PL_SYSTEM) {
+		int ret = ttm_bo_validate(bo, &sys_placement, ctx);
+
+		/* Consider -ENOMEM and -ENOSPC non-fatal. */
+		if (ret) {
+			if (ret == -ENOMEM || ret == -ENOSPC)
+				ret = -EBUSY;
+			return ret;
+		}
+	}
+
+	ttm_bo_unmap_virtual(bo);
+	lret = ttm_bo_wait_ctx(bo, ctx);
+	if (lret < 0)
+		return lret;
+
+	if (bo->bulk_move) {
+		spin_lock(&bo->bdev->lru_lock);
+		ttm_resource_del_bulk_move(bo->resource, bo);
+		spin_unlock(&bo->bdev->lru_lock);
+	}
+
+	lret = ttm_tt_backup(bo->bdev, tt, (struct ttm_backup_flags)
+			     {.purge = flags.purge,
+			      .writeback = flags.writeback});
+
+	if (lret <= 0 && bo->bulk_move) {
+		spin_lock(&bo->bdev->lru_lock);
+		ttm_resource_add_bulk_move(bo->resource, bo);
+		spin_unlock(&bo->bdev->lru_lock);
+	}
+
+	if (lret < 0 && lret != -EINTR)
+		return -EBUSY;
+
+	return lret;
+}
+EXPORT_SYMBOL(ttm_bo_shrink);
+
+/**
+ * ttm_bo_shrink_suitable() - Whether a bo is suitable for shinking
+ * @ctx: The struct ttm_operation_ctx governing the shrinking.
+ * @bo: The candidate for shrinking.
+ *
+ * Check whether the object, given the information available to TTM,
+ * is suitable for shinking, This function can and should be used
+ * before attempting to shrink an object.
+ *
+ * Return: true if suitable. false if not.
+ */
+bool ttm_bo_shrink_suitable(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx)
+{
+	return bo->ttm && ttm_tt_is_populated(bo->ttm) && !bo->pin_count &&
+		(!ctx->no_wait_gpu ||
+		 dma_resv_test_signaled(bo->base.resv, DMA_RESV_USAGE_BOOKKEEP));
+}
+EXPORT_SYMBOL(ttm_bo_shrink_suitable);
+
+/**
+ * ttm_bo_shrink_avoid_wait() - Whether to avoid waiting for GPU
+ * during shrinking
+ *
+ * In some situations, like direct reclaim, waiting (in particular gpu waiting)
+ * should be avoided since it may stall a system that could otherwise make progress
+ * shrinking something else less time consuming.
+ *
+ * Return: true if gpu waiting should be avoided, false if not.
+ */
+bool ttm_bo_shrink_avoid_wait(void)
+{
+	return !current_is_kswapd();
+}
+EXPORT_SYMBOL(ttm_bo_shrink_avoid_wait);
diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index c9eba76d5143..83b10706ba89 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -41,12 +41,20 @@
 #include <asm/set_memory.h>
 #endif
 
+#include <drm/ttm/ttm_backup.h>
 #include <drm/ttm/ttm_pool.h>
 #include <drm/ttm/ttm_tt.h>
 #include <drm/ttm/ttm_bo.h>
 
 #include "ttm_module.h"
 
+#ifdef CONFIG_FAULT_INJECTION
+#include <linux/fault-inject.h>
+static DECLARE_FAULT_ATTR(backup_fault_inject);
+#else
+#define should_fail(...) false
+#endif
+
 /**
  * struct ttm_pool_dma - Helper object for coherent DMA mappings
  *
@@ -75,6 +83,35 @@ struct ttm_pool_alloc_state {
 	enum ttm_caching tt_caching;
 };
 
+/**
+ * struct ttm_pool_tt_restore - State representing restore from backup
+ * @pool: The pool used for page allocation while restoring.
+ * @snapshot_alloc: A snapshot of the most recent struct ttm_pool_alloc_state.
+ * @alloced_page: Pointer to the page most recently allocated from a pool or system.
+ * @first_dma: The dma address corresponding to @alloced_page if dma_mapping
+ * is requested.
+ * @alloced_pages: The number of allocated pages present in the struct ttm_tt
+ * page vector from this restore session.
+ * @restored_pages: The number of 4K pages restored for @alloced_page (which
+ * is typically a multi-order page).
+ * @page_caching: The struct ttm_tt requested caching
+ * @order: The order of @alloced_page.
+ *
+ * Recovery from backup might fail when we've recovered less than the
+ * full ttm_tt. In order not to loose any data (yet), keep information
+ * around that allows us to restart a failed ttm backup recovery.
+ */
+struct ttm_pool_tt_restore {
+	struct ttm_pool *pool;
+	struct ttm_pool_alloc_state snapshot_alloc;
+	struct page *alloced_page;
+	dma_addr_t first_dma;
+	pgoff_t alloced_pages;
+	pgoff_t restored_pages;
+	enum ttm_caching page_caching;
+	unsigned int order;
+};
+
 static unsigned long page_pool_size;
 
 MODULE_PARM_DESC(page_pool_size, "Number of pages in the WC/UC/DMA pool");
@@ -199,12 +236,11 @@ static int ttm_pool_apply_caching(struct ttm_pool_alloc_state *alloc)
 	return 0;
 }
 
-/* Map pages of 1 << order size and fill the DMA address array  */
+/* DMA Map pages of 1 << order size and return the resulting dma_address. */
 static int ttm_pool_map(struct ttm_pool *pool, unsigned int order,
-			struct page *p, dma_addr_t **dma_addr)
+			struct page *p, dma_addr_t *dma_addr)
 {
 	dma_addr_t addr;
-	unsigned int i;
 
 	if (pool->use_dma_alloc) {
 		struct ttm_pool_dma *dma = (void *)p->private;
@@ -218,10 +254,7 @@ static int ttm_pool_map(struct ttm_pool *pool, unsigned int order,
 			return -EFAULT;
 	}
 
-	for (i = 1 << order; i ; --i) {
-		*(*dma_addr)++ = addr;
-		addr += PAGE_SIZE;
-	}
+	*dma_addr = addr;
 
 	return 0;
 }
@@ -372,6 +405,196 @@ static unsigned int ttm_pool_page_order(struct ttm_pool *pool, struct page *p)
 }
 
 /*
+ * Split larger pages so that we can free each PAGE_SIZE page as soon
+ * as it has been backed up, in order to avoid memory pressure during
+ * reclaim.
+ */
+static void ttm_pool_split_for_swap(struct ttm_pool *pool, struct page *p)
+{
+	unsigned int order = ttm_pool_page_order(pool, p);
+	pgoff_t nr;
+
+	if (!order)
+		return;
+
+	split_page(p, order);
+	nr = 1UL << order;
+	while (nr--)
+		(p++)->private = 0;
+}
+
+/**
+ * DOC: Partial backup and restoration of a struct ttm_tt.
+ *
+ * Swapout using ttm_backup_backup_page() and swapin using
+ * ttm_backup_copy_page() may fail.
+ * The former most likely due to lack of swap-space or memory, the latter due
+ * to lack of memory or because of signal interruption during waits.
+ *
+ * Backup failure is easily handled by using a ttm_tt pages vector that holds
+ * both backup handles and page pointers. This has to be taken into account when
+ * restoring such a ttm_tt from backup, and when freeing it while backed up.
+ * When restoring, for simplicity, new pages are actually allocated from the
+ * pool and the contents of any old pages are copied in and then the old pages
+ * are released.
+ *
+ * For restoration failures, the struct ttm_pool_tt_restore holds sufficient state
+ * to be able to resume an interrupted restore, and that structure is freed once
+ * the restoration is complete. If the struct ttm_tt is destroyed while there
+ * is a valid struct ttm_pool_tt_restore attached, that is also properly taken
+ * care of.
+ */
+
+/* Is restore ongoing for the currently allocated page? */
+static bool ttm_pool_restore_valid(const struct ttm_pool_tt_restore *restore)
+{
+	return restore && restore->restored_pages < (1 << restore->order);
+}
+
+/* DMA unmap and free a multi-order page, either to the relevant pool or to system. */
+static pgoff_t ttm_pool_unmap_and_free(struct ttm_pool *pool, struct page *page,
+				       const dma_addr_t *dma_addr, enum ttm_caching caching)
+{
+	struct ttm_pool_type *pt = NULL;
+	unsigned int order;
+	pgoff_t nr;
+
+	if (pool) {
+		order = ttm_pool_page_order(pool, page);
+		nr = (1UL << order);
+		if (dma_addr)
+			ttm_pool_unmap(pool, *dma_addr, nr);
+
+		pt = ttm_pool_select_type(pool, caching, order);
+	} else {
+		order = page->private;
+		nr = (1UL << order);
+	}
+
+	if (pt)
+		ttm_pool_type_give(pt, page);
+	else
+		ttm_pool_free_page(pool, caching, order, page);
+
+	return nr;
+}
+
+/* Populate the page-array using the most recent allocated multi-order page. */
+static void ttm_pool_allocated_page_commit(struct page *allocated,
+					   dma_addr_t first_dma,
+					   struct ttm_pool_alloc_state *alloc,
+					   pgoff_t nr)
+{
+	pgoff_t i;
+
+	for (i = 0; i < nr; ++i)
+		*alloc->pages++ = allocated++;
+
+	alloc->remaining_pages -= nr;
+
+	if (!alloc->dma_addr)
+		return;
+
+	for (i = 0; i < nr; ++i) {
+		*alloc->dma_addr++ = first_dma;
+		first_dma += PAGE_SIZE;
+	}
+}
+
+/*
+ * When restoring, restore backed-up content to the newly allocated page and
+ * if successful, populate the page-table and dma-address arrays.
+ */
+static int ttm_pool_restore_commit(struct ttm_pool_tt_restore *restore,
+				   struct ttm_backup *backup,
+				   const struct ttm_operation_ctx *ctx,
+				   struct ttm_pool_alloc_state *alloc)
+
+{
+	pgoff_t i, nr = 1UL << restore->order;
+	struct page **first_page = alloc->pages;
+	struct page *p;
+	int ret = 0;
+
+	for (i = restore->restored_pages; i < nr; ++i) {
+		p = first_page[i];
+		if (ttm_backup_page_ptr_is_handle(p)) {
+			unsigned long handle = ttm_backup_page_ptr_to_handle(p);
+
+			if (IS_ENABLED(CONFIG_FAULT_INJECTION) && ctx->interruptible &&
+			    should_fail(&backup_fault_inject, 1)) {
+				ret = -EINTR;
+				break;
+			}
+
+			if (handle == 0) {
+				restore->restored_pages++;
+				continue;
+			}
+
+			ret = ttm_backup_copy_page(backup, restore->alloced_page + i,
+						   handle, ctx->interruptible);
+			if (ret)
+				break;
+
+			ttm_backup_drop(backup, handle);
+		} else if (p) {
+			/*
+			 * We could probably avoid splitting the old page
+			 * using clever logic, but ATM we don't care, as
+			 * we prioritize releasing memory ASAP. Note that
+			 * here, the old retained page is always write-back
+			 * cached.
+			 */
+			ttm_pool_split_for_swap(restore->pool, p);
+			copy_highpage(restore->alloced_page + i, p);
+			__free_pages(p, 0);
+		}
+
+		restore->restored_pages++;
+		first_page[i] = ttm_backup_handle_to_page_ptr(0);
+	}
+
+	if (ret) {
+		if (!restore->restored_pages) {
+			dma_addr_t *dma_addr = alloc->dma_addr ? &restore->first_dma : NULL;
+
+			ttm_pool_unmap_and_free(restore->pool, restore->alloced_page,
+						dma_addr, restore->page_caching);
+			restore->restored_pages = nr;
+		}
+		return ret;
+	}
+
+	ttm_pool_allocated_page_commit(restore->alloced_page, restore->first_dma,
+				       alloc, nr);
+	if (restore->page_caching == alloc->tt_caching || PageHighMem(restore->alloced_page))
+		alloc->caching_divide = alloc->pages;
+	restore->snapshot_alloc = *alloc;
+	restore->alloced_pages += nr;
+
+	return 0;
+}
+
+/* If restoring, save information needed for ttm_pool_restore_commit(). */
+static void
+ttm_pool_page_allocated_restore(struct ttm_pool *pool, unsigned int order,
+				struct page *p,
+				enum ttm_caching page_caching,
+				dma_addr_t first_dma,
+				struct ttm_pool_tt_restore *restore,
+				const struct ttm_pool_alloc_state *alloc)
+{
+	restore->pool = pool;
+	restore->order = order;
+	restore->restored_pages = 0;
+	restore->page_caching = page_caching;
+	restore->first_dma = first_dma;
+	restore->alloced_page = p;
+	restore->snapshot_alloc = *alloc;
+}
+
+/*
  * Called when we got a page, either from a pool or newly allocated.
  * if needed, dma map the page and populate the dma address array.
  * Populate the page address array.
@@ -380,10 +603,11 @@ static unsigned int ttm_pool_page_order(struct ttm_pool *pool, struct page *p)
  */
 static int ttm_pool_page_allocated(struct ttm_pool *pool, unsigned int order,
 				   struct page *p, enum ttm_caching page_caching,
-				   struct ttm_pool_alloc_state *alloc)
+				   struct ttm_pool_alloc_state *alloc,
+				   struct ttm_pool_tt_restore *restore)
 {
-	pgoff_t i, nr = 1UL << order;
 	bool caching_consistent;
+	dma_addr_t first_dma;
 	int r = 0;
 
 	caching_consistent = (page_caching == alloc->tt_caching) || PageHighMem(p);
@@ -395,17 +619,20 @@ static int ttm_pool_page_allocated(struct ttm_pool *pool, unsigned int order,
 	}
 
 	if (alloc->dma_addr) {
-		r = ttm_pool_map(pool, order, p, &alloc->dma_addr);
+		r = ttm_pool_map(pool, order, p, &first_dma);
 		if (r)
 			return r;
 	}
 
-	alloc->remaining_pages -= nr;
-	for (i = 0; i < nr; ++i)
-		*alloc->pages++ = p++;
+	if (restore) {
+		ttm_pool_page_allocated_restore(pool, order, p, page_caching,
+						first_dma, restore, alloc);
+	} else {
+		ttm_pool_allocated_page_commit(p, first_dma, alloc, 1UL << order);
 
-	if (caching_consistent)
-		alloc->caching_divide = alloc->pages;
+		if (caching_consistent)
+			alloc->caching_divide = alloc->pages;
+	}
 
 	return 0;
 }
@@ -428,22 +655,24 @@ static void ttm_pool_free_range(struct ttm_pool *pool, struct ttm_tt *tt,
 				pgoff_t start_page, pgoff_t end_page)
 {
 	struct page **pages = &tt->pages[start_page];
-	unsigned int order;
+	struct ttm_backup *backup = tt->backup;
 	pgoff_t i, nr;
 
 	for (i = start_page; i < end_page; i += nr, pages += nr) {
-		struct ttm_pool_type *pt = NULL;
+		struct page *p = *pages;
 
-		order = ttm_pool_page_order(pool, *pages);
-		nr = (1UL << order);
-		if (tt->dma_address)
-			ttm_pool_unmap(pool, tt->dma_address[i], nr);
+		nr = 1;
+		if (ttm_backup_page_ptr_is_handle(p)) {
+			unsigned long handle = ttm_backup_page_ptr_to_handle(p);
 
-		pt = ttm_pool_select_type(pool, caching, order);
-		if (pt)
-			ttm_pool_type_give(pt, *pages);
-		else
-			ttm_pool_free_page(pool, caching, order, *pages);
+			if (handle != 0)
+				ttm_backup_drop(backup, handle);
+		} else if (p) {
+			dma_addr_t *dma_addr = tt->dma_address ?
+				tt->dma_address + i : NULL;
+
+			nr = ttm_pool_unmap_and_free(pool, p, dma_addr, caching);
+		}
 	}
 }
 
@@ -467,22 +696,11 @@ static unsigned int ttm_pool_alloc_find_order(unsigned int highest,
 	return min_t(unsigned int, highest, __fls(alloc->remaining_pages));
 }
 
-/**
- * ttm_pool_alloc - Fill a ttm_tt object
- *
- * @pool: ttm_pool to use
- * @tt: ttm_tt object to fill
- * @ctx: operation context
- *
- * Fill the ttm_tt object with pages and also make sure to DMA map them when
- * necessary.
- *
- * Returns: 0 on successe, negative error code otherwise.
- */
-int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt,
-		   struct ttm_operation_ctx *ctx)
+static int __ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt,
+			    const struct ttm_operation_ctx *ctx,
+			    struct ttm_pool_alloc_state *alloc,
+			    struct ttm_pool_tt_restore *restore)
 {
-	struct ttm_pool_alloc_state alloc;
 	enum ttm_caching page_caching;
 	gfp_t gfp_flags = GFP_USER;
 	pgoff_t caching_divide;
@@ -491,10 +709,8 @@ int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt,
 	struct page *p;
 	int r;
 
-	ttm_pool_alloc_state_init(tt, &alloc);
-
-	WARN_ON(!alloc.remaining_pages || ttm_tt_is_populated(tt));
-	WARN_ON(alloc.dma_addr && !pool->dev);
+	WARN_ON(!alloc->remaining_pages || ttm_tt_is_populated(tt));
+	WARN_ON(alloc->dma_addr && !pool->dev);
 
 	if (tt->page_flags & TTM_TT_FLAG_ZERO_ALLOC)
 		gfp_flags |= __GFP_ZERO;
@@ -509,9 +725,9 @@ int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt,
 
 	page_caching = tt->caching;
 	allow_pools = true;
-	for (order = ttm_pool_alloc_find_order(MAX_PAGE_ORDER, &alloc);
-	     alloc.remaining_pages;
-	     order = ttm_pool_alloc_find_order(order, &alloc)) {
+	for (order = ttm_pool_alloc_find_order(MAX_PAGE_ORDER, alloc);
+	     alloc->remaining_pages;
+	     order = ttm_pool_alloc_find_order(order, alloc)) {
 		struct ttm_pool_type *pt;
 
 		/* First, try to allocate a page from a pool if one exists. */
@@ -541,31 +757,121 @@ int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt,
 			r = -ENOMEM;
 			goto error_free_all;
 		}
-		r = ttm_pool_page_allocated(pool, order, p, page_caching, &alloc);
+		r = ttm_pool_page_allocated(pool, order, p, page_caching, alloc,
+					    restore);
 		if (r)
 			goto error_free_page;
+
+		if (ttm_pool_restore_valid(restore)) {
+			r = ttm_pool_restore_commit(restore, tt->backup, ctx, alloc);
+			if (r)
+				goto error_free_all;
+		}
 	}
 
-	r = ttm_pool_apply_caching(&alloc);
+	r = ttm_pool_apply_caching(alloc);
 	if (r)
 		goto error_free_all;
 
+	kfree(tt->restore);
+	tt->restore = NULL;
+
 	return 0;
 
 error_free_page:
 	ttm_pool_free_page(pool, page_caching, order, p);
 
 error_free_all:
-	caching_divide = alloc.caching_divide - tt->pages;
+	if (tt->restore)
+		return r;
+
+	caching_divide = alloc->caching_divide - tt->pages;
 	ttm_pool_free_range(pool, tt, tt->caching, 0, caching_divide);
 	ttm_pool_free_range(pool, tt, ttm_cached, caching_divide,
-			    tt->num_pages - alloc.remaining_pages);
+			    tt->num_pages - alloc->remaining_pages);
 
 	return r;
 }
+
+/**
+ * ttm_pool_alloc - Fill a ttm_tt object
+ *
+ * @pool: ttm_pool to use
+ * @tt: ttm_tt object to fill
+ * @ctx: operation context
+ *
+ * Fill the ttm_tt object with pages and also make sure to DMA map them when
+ * necessary.
+ *
+ * Returns: 0 on successe, negative error code otherwise.
+ */
+int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt,
+		   struct ttm_operation_ctx *ctx)
+{
+	struct ttm_pool_alloc_state alloc;
+
+	if (WARN_ON(ttm_tt_is_backed_up(tt)))
+		return -EINVAL;
+
+	ttm_pool_alloc_state_init(tt, &alloc);
+
+	return __ttm_pool_alloc(pool, tt, ctx, &alloc, NULL);
+}
 EXPORT_SYMBOL(ttm_pool_alloc);
 
 /**
+ * ttm_pool_restore_and_alloc - Fill a ttm_tt, restoring previously backed-up
+ * content.
+ *
+ * @pool: ttm_pool to use
+ * @tt: ttm_tt object to fill
+ * @ctx: operation context
+ *
+ * Fill the ttm_tt object with pages and also make sure to DMA map them when
+ * necessary. Read in backed-up content.
+ *
+ * Returns: 0 on successe, negative error code otherwise.
+ */
+int ttm_pool_restore_and_alloc(struct ttm_pool *pool, struct ttm_tt *tt,
+			       const struct ttm_operation_ctx *ctx)
+{
+	struct ttm_pool_alloc_state alloc;
+
+	if (WARN_ON(!ttm_tt_is_backed_up(tt)))
+		return -EINVAL;
+
+	if (!tt->restore) {
+		gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
+
+		ttm_pool_alloc_state_init(tt, &alloc);
+		if (ctx->gfp_retry_mayfail)
+			gfp |= __GFP_RETRY_MAYFAIL;
+
+		tt->restore = kzalloc(sizeof(*tt->restore), gfp);
+		if (!tt->restore)
+			return -ENOMEM;
+
+		tt->restore->snapshot_alloc = alloc;
+		tt->restore->pool = pool;
+		tt->restore->restored_pages = 1;
+	} else {
+		struct ttm_pool_tt_restore *restore = tt->restore;
+		int ret;
+
+		alloc = restore->snapshot_alloc;
+		if (ttm_pool_restore_valid(tt->restore)) {
+			ret = ttm_pool_restore_commit(restore, tt->backup, ctx, &alloc);
+			if (ret)
+				return ret;
+		}
+		if (!alloc.remaining_pages)
+			return 0;
+	}
+
+	return __ttm_pool_alloc(pool, tt, ctx, &alloc, tt->restore);
+}
+
+/**
  * ttm_pool_free - Free the backing pages from a ttm_tt object
  *
  * @pool: Pool to give pages back to.
@@ -583,6 +889,169 @@ void ttm_pool_free(struct ttm_pool *pool, struct ttm_tt *tt)
 EXPORT_SYMBOL(ttm_pool_free);
 
 /**
+ * ttm_pool_drop_backed_up() - Release content of a swapped-out struct ttm_tt
+ * @tt: The struct ttm_tt.
+ *
+ * Release handles with associated content or any remaining pages of
+ * a backed-up struct ttm_tt.
+ */
+void ttm_pool_drop_backed_up(struct ttm_tt *tt)
+{
+	struct ttm_pool_tt_restore *restore;
+	pgoff_t start_page = 0;
+
+	WARN_ON(!ttm_tt_is_backed_up(tt));
+
+	restore = tt->restore;
+
+	/*
+	 * Unmap and free any uncommitted restore page.
+	 * any tt page-array backup entries already read back has
+	 * been cleared already
+	 */
+	if (ttm_pool_restore_valid(restore)) {
+		dma_addr_t *dma_addr = tt->dma_address ? &restore->first_dma : NULL;
+
+		ttm_pool_unmap_and_free(restore->pool, restore->alloced_page,
+					dma_addr, restore->page_caching);
+		restore->restored_pages = 1UL << restore->order;
+	}
+
+	/*
+	 * If a restore is ongoing, part of the tt pages may have a
+	 * caching different than writeback.
+	 */
+	if (restore) {
+		pgoff_t mid = restore->snapshot_alloc.caching_divide - tt->pages;
+
+		start_page = restore->alloced_pages;
+		WARN_ON(mid > start_page);
+		/* Pages that might be dma-mapped and non-cached */
+		ttm_pool_free_range(restore->pool, tt, tt->caching,
+				    0, mid);
+		/* Pages that might be dma-mapped but cached */
+		ttm_pool_free_range(restore->pool, tt, ttm_cached,
+				    mid, restore->alloced_pages);
+		kfree(restore);
+		tt->restore = NULL;
+	}
+
+	ttm_pool_free_range(NULL, tt, ttm_cached, start_page, tt->num_pages);
+}
+
+/**
+ * ttm_pool_backup() - Back up or purge a struct ttm_tt
+ * @pool: The pool used when allocating the struct ttm_tt.
+ * @tt: The struct ttm_tt.
+ * @flags: Flags to govern the backup behaviour.
+ *
+ * Back up or purge a struct ttm_tt. If @purge is true, then
+ * all pages will be freed directly to the system rather than to the pool
+ * they were allocated from, making the function behave similarly to
+ * ttm_pool_free(). If @purge is false the pages will be backed up instead,
+ * exchanged for handles.
+ * A subsequent call to ttm_pool_restore_and_alloc() will then read back the content and
+ * a subsequent call to ttm_pool_drop_backed_up() will drop it.
+ * If backup of a page fails for whatever reason, @ttm will still be
+ * partially backed up, retaining those pages for which backup fails.
+ * In that case, this function can be retried, possibly after freeing up
+ * memory resources.
+ *
+ * Return: Number of pages actually backed up or freed, or negative
+ * error code on error.
+ */
+long ttm_pool_backup(struct ttm_pool *pool, struct ttm_tt *tt,
+		     const struct ttm_backup_flags *flags)
+{
+	struct ttm_backup *backup = tt->backup;
+	struct page *page;
+	unsigned long handle;
+	gfp_t alloc_gfp;
+	gfp_t gfp;
+	int ret = 0;
+	pgoff_t shrunken = 0;
+	pgoff_t i, num_pages;
+
+	if (WARN_ON(ttm_tt_is_backed_up(tt)))
+		return -EINVAL;
+
+	if ((!ttm_backup_bytes_avail() && !flags->purge) ||
+	    pool->use_dma_alloc || ttm_tt_is_backed_up(tt))
+		return -EBUSY;
+
+#ifdef CONFIG_X86
+	/* Anything returned to the system needs to be cached. */
+	if (tt->caching != ttm_cached)
+		set_pages_array_wb(tt->pages, tt->num_pages);
+#endif
+
+	if (tt->dma_address || flags->purge) {
+		for (i = 0; i < tt->num_pages; i += num_pages) {
+			unsigned int order;
+
+			page = tt->pages[i];
+			if (unlikely(!page)) {
+				num_pages = 1;
+				continue;
+			}
+
+			order = ttm_pool_page_order(pool, page);
+			num_pages = 1UL << order;
+			if (tt->dma_address)
+				ttm_pool_unmap(pool, tt->dma_address[i],
+					       num_pages);
+			if (flags->purge) {
+				shrunken += num_pages;
+				page->private = 0;
+				__free_pages(page, order);
+				memset(tt->pages + i, 0,
+				       num_pages * sizeof(*tt->pages));
+			}
+		}
+	}
+
+	if (flags->purge)
+		return shrunken;
+
+	if (pool->use_dma32)
+		gfp = GFP_DMA32;
+	else
+		gfp = GFP_HIGHUSER;
+
+	alloc_gfp = GFP_KERNEL | __GFP_HIGH | __GFP_NOWARN | __GFP_RETRY_MAYFAIL;
+
+	num_pages = tt->num_pages;
+
+	/* Pretend doing fault injection by shrinking only half of the pages. */
+	if (IS_ENABLED(CONFIG_FAULT_INJECTION) && should_fail(&backup_fault_inject, 1))
+		num_pages = DIV_ROUND_UP(num_pages, 2);
+
+	for (i = 0; i < num_pages; ++i) {
+		s64 shandle;
+
+		page = tt->pages[i];
+		if (unlikely(!page))
+			continue;
+
+		ttm_pool_split_for_swap(pool, page);
+
+		shandle = ttm_backup_backup_page(backup, page, flags->writeback, i,
+						 gfp, alloc_gfp);
+		if (shandle < 0) {
+			/* We allow partially shrunken tts */
+			ret = shandle;
+			break;
+		}
+		handle = shandle;
+		tt->pages[i] = ttm_backup_handle_to_page_ptr(handle);
+		put_page(page);
+		shrunken++;
+	}
+
+	return shrunken ? shrunken : ret;
+}
+
+/**
  * ttm_pool_init - Initialize a pool
  *
  * @pool: the pool to initialize
@@ -843,6 +1312,10 @@ int ttm_pool_mgr_init(unsigned long num_pages)
 			    &ttm_pool_debugfs_globals_fops);
 	debugfs_create_file("page_pool_shrink", 0400, ttm_debugfs_root, NULL,
 			    &ttm_pool_debugfs_shrink_fops);
+#ifdef CONFIG_FAULT_INJECTION
+	fault_create_debugfs_attr("backup_fault_inject", ttm_debugfs_root,
+				  &backup_fault_inject);
+#endif
 #endif
 
 	mm_shrinker = shrinker_alloc(0, "drm-ttm_pool");
diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
index 3baf215eca23..df0aa6c4b8b8 100644
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -40,6 +40,7 @@
 #include <drm/drm_cache.h>
 #include <drm/drm_device.h>
 #include <drm/drm_util.h>
+#include <drm/ttm/ttm_backup.h>
 #include <drm/ttm/ttm_bo.h>
 #include <drm/ttm/ttm_tt.h>
 
@@ -158,6 +159,8 @@ static void ttm_tt_init_fields(struct ttm_tt *ttm,
 	ttm->swap_storage = NULL;
 	ttm->sg = bo->sg;
 	ttm->caching = caching;
+	ttm->restore = NULL;
+	ttm->backup = NULL;
 }
 
 int ttm_tt_init(struct ttm_tt *ttm, struct ttm_buffer_object *bo,
@@ -182,6 +185,13 @@ void ttm_tt_fini(struct ttm_tt *ttm)
 		fput(ttm->swap_storage);
 	ttm->swap_storage = NULL;
 
+	if (ttm_tt_is_backed_up(ttm))
+		ttm_pool_drop_backed_up(ttm);
+	if (ttm->backup) {
+		ttm_backup_fini(ttm->backup);
+		ttm->backup = NULL;
+	}
+
 	if (ttm->pages)
 		kvfree(ttm->pages);
 	else
@@ -254,6 +264,49 @@ out_err:
 EXPORT_SYMBOL_FOR_TESTS_ONLY(ttm_tt_swapin);
 
 /**
+ * ttm_tt_backup() - Helper to back up a struct ttm_tt.
+ * @bdev: The TTM device.
+ * @tt: The struct ttm_tt.
+ * @flags: Flags that govern the backup behaviour.
+ *
+ * Update the page accounting and call ttm_pool_shrink_tt to free pages
+ * or back them up.
+ *
+ * Return: Number of pages freed or swapped out, or negative error code on
+ * error.
+ */
+long ttm_tt_backup(struct ttm_device *bdev, struct ttm_tt *tt,
+		   const struct ttm_backup_flags flags)
+{
+	long ret;
+
+	if (WARN_ON(IS_ERR_OR_NULL(tt->backup)))
+		return 0;
+
+	ret = ttm_pool_backup(&bdev->pool, tt, &flags);
+	if (ret > 0) {
+		tt->page_flags &= ~TTM_TT_FLAG_PRIV_POPULATED;
+		tt->page_flags |= TTM_TT_FLAG_BACKED_UP;
+	}
+
+	return ret;
+}
+
+int ttm_tt_restore(struct ttm_device *bdev, struct ttm_tt *tt,
+		   const struct ttm_operation_ctx *ctx)
+{
+	int ret = ttm_pool_restore_and_alloc(&bdev->pool, tt, ctx);
+
+	if (ret)
+		return ret;
+
+	tt->page_flags &= ~TTM_TT_FLAG_BACKED_UP;
+
+	return 0;
+}
+EXPORT_SYMBOL(ttm_tt_restore);
+
+/**
  * ttm_tt_swapout - swap out tt object
  *
  * @bdev: TTM device structure.
@@ -348,6 +401,7 @@ int ttm_tt_populate(struct ttm_device *bdev,
 		goto error;
 
 	ttm->page_flags |= TTM_TT_FLAG_PRIV_POPULATED;
+	ttm->page_flags &= ~TTM_TT_FLAG_BACKED_UP;
 	if (unlikely(ttm->page_flags & TTM_TT_FLAG_SWAPPED)) {
 		ret = ttm_tt_swapin(ttm);
 		if (unlikely(ret != 0)) {
@@ -477,3 +531,32 @@ unsigned long ttm_tt_pages_limit(void)
 	return ttm_pages_limit;
 }
 EXPORT_SYMBOL(ttm_tt_pages_limit);
+
+/**
+ * ttm_tt_setup_backup() - Allocate and assign a backup structure for a ttm_tt
+ * @tt: The ttm_tt for wich to allocate and assign a backup structure.
+ *
+ * Assign a backup structure to be used for tt backup. This should
+ * typically be done at bo creation, to avoid allocations at shrinking
+ * time.
+ *
+ * Return: 0 on success, negative error code on failure.
+ */
+int ttm_tt_setup_backup(struct ttm_tt *tt)
+{
+	struct ttm_backup *backup =
+		ttm_backup_shmem_create(((loff_t)tt->num_pages) << PAGE_SHIFT);
+
+	if (WARN_ON_ONCE(!(tt->page_flags & TTM_TT_FLAG_EXTERNAL_MAPPABLE)))
+		return -EINVAL;
+
+	if (IS_ERR(backup))
+		return PTR_ERR(backup);
+
+	if (tt->backup)
+		ttm_backup_fini(tt->backup);
+
+	tt->backup = backup;
+	return 0;
+}
+EXPORT_SYMBOL(ttm_tt_setup_backup);