[PATCH v14 2/8] drm/ttm: Provide a shmem backup implementation
Thomas Hellström
thomas.hellstrom at linux.intel.com
Wed Nov 20 07:58:47 UTC 2024
On Tue, 2024-11-19 at 14:40 +0100, Christian König wrote:
> Am 15.11.24 um 16:01 schrieb Thomas Hellström:
> > 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 at amd.com>
> > Cc: Somalapuram Amaranath <Amaranath.Somalapuram at amd.com>
> > Cc: Matthew Brost <matthew.brost at intel.com>
> > Cc: <dri-devel at lists.freedesktop.org>
> > Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> > Reviewed-by: Matthew Brost <matthew.brost at intel.com> #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)
>
> Do I get it right that struct ttm_backup is never really defined?
Yes.
> What
> purpose does that have?
It's to make the struct ttm_backup opaque to the users of the
ttm_backup interface, so that the implementation doesn't have to worry
about the user making illegal assumptions about the implementation.
> > +{
> > + 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.
>
> Typo: gfp instead of gpf.
Sure.
>
> > + *
> > + * 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;
>
> Just that I sleep better: This can never return a folio larger than a
> page, doesn't it?
The interface definitely allows for returning larger folios, but the
individual page in the folio is selected by folio_file_page(folio,
idx).
/Thomas
>
> Apart from those background questions looks good to me.
>
> Regards,
> Christian.
>
> > +
> > + 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
>
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