On Thu, 2024-06-20 at 15:17 +0000, Matthew Brost wrote:
> 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?
It's IIRC because handle '0' has a reserved usage in the code, so
handle becomes file address space + 1.
I need to double-check that so that I don't confuse this with the
swap-space backend.
>
> > + 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.
Sure.
>
> > +{
> > + 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'?
It's used unlocked in many places in the kernel AFAICT.
>
> > + 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.
Will fix.
Thanks, Thomas
>
> 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
> >
