drivers/gpu/drm/ttm/ttm_backup.c

// SPDX-License-Identifier: MIT
/*
 * Copyright © 2024 Intel Corporation
 */

#include <drm/ttm/ttm_backup.h>

#include <linux/export.h>
#include <linux/swap.h>

#include "ttm_pool_internal.h"

/*
 * 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 file *backup, pgoff_t handle)
{
	loff_t start = ttm_backup_handle_to_shmem_idx(handle);

	start <<= PAGE_SHIFT;
	shmem_truncate_range(file_inode(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 interruptible or at least killable.
 * @additional_gfp: GFP mask to add to the default GFP mask if any.
 *
 * 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 file *backup, struct page *dst,
			 pgoff_t handle, bool intr, gfp_t additional_gfp)
{
	struct address_space *mapping = backup->f_mapping;
	struct folio *from_folio;
	pgoff_t idx = ttm_backup_handle_to_shmem_idx(handle);

	from_folio = shmem_read_folio_gfp(mapping, idx, mapping_gfp_mask(mapping)
					  | additional_gfp);
	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_folio() - Backup a folio
 * @backup: The struct backup pointer to use.
 * @folio: The folio to back up.
 * @order: The allocation order of @folio.  Since TTM allocates higher-order
 *         pages without __GFP_COMP, folio_nr_pages(@folio) would always
 *         return 1; the caller must pass the true order explicitly.
 * @writeback: Whether to perform immediate writeback of the folio's pages.
 * This may have performance implications.
 * @idx: A unique integer for the first page of the folio and each struct backup.
 * This allows the backup implementation to avoid managing
 * its address space separately.
 * @folio_gfp: The gfp value used when the folio was allocated.
 * Currently unused.
 * @alloc_gfp: The gfp to be used when allocating memory.
 * @nr_pages_backed: Output. On a successful return, set to the number of
 * pages actually backed up, which may be less than (1 << @order)
 * if an -ENOMEM was encountered mid-folio.
 *
 * 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 for the first backed-up page on success (handles for
 * subsequent pages follow sequentially). -ENOMEM if no pages could be backed
 * up. Any other negative error code if a non-ENOMEM failure occurred; in that
 * case any pages backed up so far are truncated before returning.
 */
s64
ttm_backup_backup_folio(struct file *backup, struct folio *folio,
			unsigned int order, bool writeback, pgoff_t idx,
			gfp_t folio_gfp, gfp_t alloc_gfp,
			pgoff_t *nr_pages_backed)
{
	struct address_space *mapping = backup->f_mapping;
	int nr_pages = 1 << order;
	struct folio *to_folio;
	int ret, i;

	*nr_pages_backed = 0;

	for (i = 0; i < nr_pages; ) {
		int to_nr, j;

		/*
		 * Only inject past the first subpage so *nr_pages_backed is
		 * always > 0 here, matching a genuine mid-compound -ENOMEM
		 * and driving the caller's reactive split fallback instead
		 * of an early, no-progress failure.
		 */
		if (IS_ENABLED(CONFIG_FAULT_INJECTION) && i &&
		    ttm_backup_fault_inject_folio())
			to_folio = ERR_PTR(-ENOMEM);
		else
			to_folio = shmem_read_folio_gfp(mapping, idx + i, alloc_gfp);
		if (IS_ERR(to_folio)) {
			int err = PTR_ERR(to_folio);

			if (err == -ENOMEM && *nr_pages_backed)
				return ttm_backup_shmem_idx_to_handle(idx);

			if (*nr_pages_backed) {
				shmem_truncate_range(file_inode(backup),
						     (loff_t)idx << PAGE_SHIFT,
						     ((loff_t)(idx + i) << PAGE_SHIFT) - 1);
				/*
				 * The pages just truncated are no longer
				 * backed up; don't let the caller mistake
				 * them for valid handles.
				 */
				*nr_pages_backed = 0;
			}
			return err;
		}

		to_nr = min_t(int, nr_pages - i,
			      folio_next_index(to_folio) - (idx + i));

		folio_mark_accessed(to_folio);
		folio_lock(to_folio);
		folio_mark_dirty(to_folio);

		for (j = 0; j < to_nr; j++)
			copy_highpage(folio_file_page(to_folio, idx + i + j),
				      folio_page(folio, i + j));

		if (writeback && !folio_mapped(to_folio) &&
		    folio_clear_dirty_for_io(to_folio)) {
			folio_set_reclaim(to_folio);
		ret = shmem_write_folio(to_folio);
			if (!folio_test_writeback(to_folio))
				folio_clear_reclaim(to_folio);
			if (ret == AOP_WRITEPAGE_ACTIVATE)
				folio_unlock(to_folio);
		} else {
			folio_unlock(to_folio);
		}

		folio_put(to_folio);
		i += to_nr;
		*nr_pages_backed = i;
	}

	return ttm_backup_shmem_idx_to_handle(idx);
}

/**
 * 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 file *backup)
{
	fput(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 file on success,
 * an error pointer on error.
 */
struct file *ttm_backup_shmem_create(loff_t size)
{
	return shmem_file_setup("ttm shmem backup", size,
				EMPTY_VMA_FLAGS);
}