Provide a standalone shmem backup implementation.
Given the ttm_backup interface, this could
later on be extended to providing other backup
implementation than shmem, with one use-case being
GPU swapout to a user-provided fd.
v5:
- Fix a UAF. (kernel test robot, Dan Carptenter)
v6:
- Rename ttm_backup_shmem_copy_page() function argument
(Matthew Brost)
- Add some missing documentation
v8:
- Use folio_file_page to get to the page we want to writeback
instead of using the first page of the folio.
v13:
- Remove the base class abstraction (Christian König)
- Include ttm_backup_bytes_avail().
v14:
- Fix kerneldoc for ttm_backup_bytes_avail() (0-day)
- Work around casting of __randomize_layout struct pointer (0-day)
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Somalapuram Amaranath <Amaranath.Somalapuram@xxxxxxx>
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: <dri-devel@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Reviewed-by: Matthew Brost <matthew.brost@xxxxxxxxx> #v13
---
drivers/gpu/drm/ttm/Makefile | 2 +-
drivers/gpu/drm/ttm/ttm_backup.c | 204 +++++++++++++++++++++++++++++++
include/drm/ttm/ttm_backup.h | 74 +++++++++++
3 files changed, 279 insertions(+), 1 deletion(-)
create mode 100644 drivers/gpu/drm/ttm/ttm_backup.c
create mode 100644 include/drm/ttm/ttm_backup.h
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..bf16bb0c594e
--- /dev/null
+++ b/drivers/gpu/drm/ttm/ttm_backup.c
@@ -0,0 +1,204 @@
+// 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 gpf 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. 0 on failure.
+ * (This is following the swp_entry_t convention).
+ *
+ * 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.
+ */
+unsigned long
+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 handle;
+
+ 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 */
+ 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/include/drm/ttm/ttm_backup.h b/include/drm/ttm/ttm_backup.h
new file mode 100644
index 000000000000..20609da7e281
--- /dev/null
+++ b/include/drm/ttm/ttm_backup.h
@@ -0,0 +1,74 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2024 Intel Corporation
+ */
+
+#ifndef _TTM_BACKUP_H_
+#define _TTM_BACKUP_H_
+
+#include <linux/mm_types.h>
+#include <linux/shmem_fs.h>
+
+struct ttm_backup;
+
+/**
+ * ttm_backup_handle_to_page_ptr() - Convert handle to struct page pointer
+ * @handle: The handle to convert.
+ *
+ * Converts an opaque handle received from the
+ * struct ttm_backoup_ops::backup_page() function to an (invalid)
+ * struct page pointer suitable for a struct page array.
+ *
+ * Return: An (invalid) struct page pointer.
+ */
+static inline struct page *
+ttm_backup_handle_to_page_ptr(unsigned long handle)
+{
+ return (struct page *)(handle << 1 | 1);
+}
+
+/**
+ * ttm_backup_page_ptr_is_handle() - Whether a struct page pointer is a handle
+ * @page: The struct page pointer to check.
+ *
+ * Return: true if the struct page pointer is a handld returned from
+ * ttm_backup_handle_to_page_ptr(). False otherwise.
+ */
+static inline bool ttm_backup_page_ptr_is_handle(const struct page *page)
+{
+ return (unsigned long)page & 1;
+}
+
+/**
+ * ttm_backup_page_ptr_to_handle() - Convert a struct page pointer to a handle
+ * @page: The struct page pointer to convert
+ *
+ * Return: The handle that was previously used in
+ * ttm_backup_handle_to_page_ptr() to obtain a struct page pointer, suitable
+ * for use as argument in the struct ttm_backup_ops drop() or
+ * copy_backed_up_page() functions.
+ */
+static inline unsigned long
+ttm_backup_page_ptr_to_handle(const struct page *page)
+{
+ WARN_ON(!ttm_backup_page_ptr_is_handle(page));
+ return (unsigned long)page >> 1;
+}
+
+void ttm_backup_drop(struct ttm_backup *backup, pgoff_t handle);
+
+int ttm_backup_copy_page(struct ttm_backup *backup, struct page *dst,
+ pgoff_t handle, bool intr);
+
+unsigned long
+ttm_backup_backup_page(struct ttm_backup *backup, struct page *page,
+ bool writeback, pgoff_t idx, gfp_t page_gfp,
+ gfp_t alloc_gfp);
+
+void ttm_backup_fini(struct ttm_backup *backup);
+
+u64 ttm_backup_bytes_avail(void);
+
+struct ttm_backup *ttm_backup_shmem_create(loff_t size);
+
+#endif
--
2.46.2
