On Tue, Jun 18, 2024 at 09:18:16AM +0200, Thomas Hellström wrote:
> Initially intended for experimenting with different backup
> solutions (shmem vs direct swap cache insertion), abstract
> the backup destination using a virtual base class.
>
> Also provide a sample implementation for shmem.
>
> While when settling on a preferred backup solution, one could
> perhaps skip the abstraction, this functionality may actually
> come in handy for configurable dedicated graphics memory
> backup to fast nvme files or similar, whithout affecting
> swap-space. Could indeed be useful for VRAM backup on S4 and
> other cases.
>
Implementation seemly makes sense and matches other similar usages of shmem /
folio functions I could find in the kernel.
A few questions / nits below.
> v5:
> - Fix a UAF. (kernel test robot, Dan Carptenter)
>
> 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>
> ---
> drivers/gpu/drm/ttm/Makefile | 2 +-
> drivers/gpu/drm/ttm/ttm_backup_shmem.c | 139 +++++++++++++++++++++++++
> include/drm/ttm/ttm_backup.h | 136 ++++++++++++++++++++++++
> 3 files changed, 276 insertions(+), 1 deletion(-)
> create mode 100644 drivers/gpu/drm/ttm/ttm_backup_shmem.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..5e980dd90e41 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_shmem.o
> ttm-$(CONFIG_AGP) += ttm_agp_backend.o
>
> obj-$(CONFIG_DRM_TTM) += ttm.o
> diff --git a/drivers/gpu/drm/ttm/ttm_backup_shmem.c b/drivers/gpu/drm/ttm/ttm_backup_shmem.c
> new file mode 100644
> index 000000000000..f5bc47734d71
> --- /dev/null
> +++ b/drivers/gpu/drm/ttm/ttm_backup_shmem.c
> @@ -0,0 +1,139 @@
> +// SPDX-License-Identifier: MIT
> +/*
> + * Copyright © 2024 Intel Corporation
> + */
> +
> +#include <drm/ttm/ttm_backup.h>
> +#include <linux/page-flags.h>
> +
> +/**
> + * struct ttm_backup_shmem - A shmem based ttm_backup subclass.
> + * @backup: The base struct ttm_backup
> + * @filp: The associated shmem object
> + */
> +struct ttm_backup_shmem {
> + struct ttm_backup backup;
> + struct file *filp;
> +};
> +
> +static struct ttm_backup_shmem *to_backup_shmem(struct ttm_backup *backup)
> +{
> + return container_of(backup, struct ttm_backup_shmem, backup);
> +}
> +
> +static void ttm_backup_shmem_drop(struct ttm_backup *backup, unsigned long handle)
> +{
> + handle -= 1;
Can you explain the -1 / +1 usage to handle in this code? Is it to test
that 'pgoff_t i' is indeed just a hint and return a different handle?
> + shmem_truncate_range(file_inode(to_backup_shmem(backup)->filp), handle,
> + handle + 1);
> +}
> +
> +static int ttm_backup_shmem_copy_page(struct ttm_backup *backup, struct page *dst,
> + unsigned long handle, bool killable)
In the vfunc definition 'killable' is named 'intr'. I'd keep the naming
consistent.
> +{
> + struct file *filp = to_backup_shmem(backup)->filp;
> + struct address_space *mapping = filp->f_mapping;
> + struct folio *from_folio;
> +
> + handle -= 1;
> + from_folio = shmem_read_folio(mapping, handle);
> + if (IS_ERR(from_folio))
> + return PTR_ERR(from_folio);
> +
> + /* Note: Use drm_memcpy_from_wc? */
> + copy_highpage(dst, folio_file_page(from_folio, handle));
> + folio_put(from_folio);
> +
> + return 0;
> +}
> +
> +static unsigned long
> +ttm_backup_shmem_backup_page(struct ttm_backup *backup, struct page *page,
> + bool writeback, pgoff_t i, gfp_t page_gfp,
> + gfp_t alloc_gfp)
> +{
> + struct file *filp = to_backup_shmem(backup)->filp;
> + struct address_space *mapping = filp->f_mapping;
> + unsigned long handle = 0;
> + struct folio *to_folio;
> + int ret;
> +
> + to_folio = shmem_read_folio_gfp(mapping, i, alloc_gfp);
> + if (IS_ERR(to_folio))
> + return handle;
> +
> + folio_mark_accessed(to_folio);
Does this not need to be after 'folio_lock'?
> + folio_lock(to_folio);
> + folio_mark_dirty(to_folio);
> + copy_highpage(folio_file_page(to_folio, i), page);
> + handle = i + 1;
> +
> + 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_page(to_folio, 0), &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;
> +}
> +
> +static void ttm_backup_shmem_fini(struct ttm_backup *backup)
> +{
> + struct ttm_backup_shmem *sbackup = to_backup_shmem(backup);
> +
> + fput(sbackup->filp);
> + kfree(sbackup);
> +}
> +
> +static const struct ttm_backup_ops ttm_backup_shmem_ops = {
> + .drop = ttm_backup_shmem_drop,
> + .copy_backed_up_page = ttm_backup_shmem_copy_page,
> + .backup_page = ttm_backup_shmem_backup_page,
> + .fini = ttm_backup_shmem_fini,
> +};
> +
> +/**
> + * 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 ttm_backup_shmem *sbackup =
> + kzalloc(sizeof(*sbackup), GFP_KERNEL | __GFP_ACCOUNT);
> + struct file *filp;
> +
> + if (!sbackup)
> + return ERR_PTR(-ENOMEM);
> +
> + filp = shmem_file_setup("ttm shmem backup", size, 0);
> + if (IS_ERR(filp)) {
> + kfree(sbackup);
> + return ERR_CAST(filp);
> + }
> +
> + sbackup->filp = filp;
> + sbackup->backup.ops = &ttm_backup_shmem_ops;
> +
> + return &sbackup->backup;
> +}
> +EXPORT_SYMBOL_GPL(ttm_backup_shmem_create);
> diff --git a/include/drm/ttm/ttm_backup.h b/include/drm/ttm/ttm_backup.h
> new file mode 100644
> index 000000000000..88e8b97a6fdc
> --- /dev/null
> +++ b/include/drm/ttm/ttm_backup.h
> @@ -0,0 +1,136 @@
> +/* 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;
> +}
> +
> +/** struct ttm_backup_ops - A struct ttm_backup backend operations */
> +struct ttm_backup_ops {
> + /**
> + * 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 (*drop)(struct ttm_backup *backup, unsigned long handle);
> +
> + /**
> + * copy_backed_up_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.
The above two are arguments flipped in order compared to function
definition.
Matt
> + * @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 (*copy_backed_up_page)(struct ttm_backup *backup, struct page *dst,
> + unsigned long handle, bool intr);
> +
> + /**
> + * 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.
> + * @i: A unique integer for each page and each struct backup.
> + * This is a hint allowing the backup backend 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 the backend needs to allocaete
> + * memory.
> + *
> + * 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
> + * backends would then split the folio internally if needed.
> + * Drawback is that the caller would then have to keep track of
> + */
> + unsigned long (*backup_page)(struct ttm_backup *backup, struct page *page,
> + bool writeback, pgoff_t i, gfp_t page_gfp,
> + gfp_t alloc_gfp);
> + /**
> + * fini - Free the struct backup resources after last use.
> + * @backup: Pointer to the struct backup whose resources to free.
> + *
> + * After a call to @fini, it's illegal to use the @backup pointer.
> + */
> + void (*fini)(struct ttm_backup *backup);
> +};
> +
> +/**
> + * struct ttm_backup - Abstract a backup backend.
> + * @ops: The operations as described above.
> + *
> + * The struct ttm_backup is intended to be subclassed by the
> + * backend implementation.
> + */
> +struct ttm_backup {
> + const struct ttm_backup_ops *ops;
> +};
> +
> +/**
> + * 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);
> +
> +#endif
> --
> 2.44.0
>
