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Current dma-buf vmap semantics require that the mapped buffer remains
in place until the corresponding vunmap has completed.
For GEM-SHMEM, this used to be guaranteed by a pin operation while creating
an S/G table in import. GEM-SHMEN can now import dma-buf objects without
creating the S/G table, so the pin is missing. Leads to page-fault errors,
such as the one shown below.
[ 102.101726] BUG: unable to handle page fault for address: ffffc90127000000
[...]
[ 102.157102] RIP: 0010:udl_compress_hline16+0x219/0x940 [udl]
[...]
[ 102.243250] Call Trace:
[ 102.245695] <TASK>
[ 102.2477V95] ? validate_chain+0x24e/0x5e0
[ 102.251805] ? __lock_acquire+0x568/0xae0
[ 102.255807] udl_render_hline+0x165/0x341 [udl]
[ 102.260338] ? __pfx_udl_render_hline+0x10/0x10 [udl]
[ 102.265379] ? local_clock_noinstr+0xb/0x100
[ 102.269642] ? __lock_release.isra.0+0x16c/0x2e0
[ 102.274246] ? mark_held_locks+0x40/0x70
[ 102.278177] udl_primary_plane_helper_atomic_update+0x43e/0x680 [udl]
[ 102.284606] ? __pfx_udl_primary_plane_helper_atomic_update+0x10/0x10 [udl]
[ 102.291551] ? lockdep_hardirqs_on_prepare.part.0+0x92/0x170
[ 102.297208] ? lockdep_hardirqs_on+0x88/0x130
[ 102.301554] ? _raw_spin_unlock_irq+0x24/0x50
[ 102.305901] ? wait_for_completion_timeout+0x2bb/0x3a0
[ 102.311028] ? drm_atomic_helper_calc_timestamping_constants+0x141/0x200
[ 102.317714] ? drm_atomic_helper_commit_planes+0x3b6/0x1030
[ 102.323279] drm_atomic_helper_commit_planes+0x3b6/0x1030
[ 102.328664] drm_atomic_helper_commit_tail+0x41/0xb0
[ 102.333622] commit_tail+0x204/0x330
[...]
[ 102.529946] ---[ end trace 0000000000000000 ]---
[ 102.651980] RIP: 0010:udl_compress_hline16+0x219/0x940 [udl]
In this stack strace, udl (based on GEM-SHMEM) imported and vmap'ed a
dma-buf from amdgpu. Amdgpu relocated the buffer, thereby invalidating the
mapping.
Provide a custom dma-buf vmap method in amdgpu that pins the object before
mapping it's buffer's pages into kernel address space. Do the opposite in
vunmap.
Note that dma-buf vmap differs from GEM vmap in how it handles relocation.
While dma-buf vmap keeps the buffer in place, GEM vmap requires the caller
to keep the buffer in place. Hence, this fix is in amdgpu's dma-buf code
instead of its GEM code.
A discussion of various approaches to solving the problem is available
at [1].
v3:
- try (GTT | VRAM); drop CPU domain (Christian)
v2:
- only use mapable domains (Christian)
- try pinning to domains in preferred order
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 660cd44659 ("drm/shmem-helper: Import dmabuf without mapping its sg_table")
Reported-by: Thomas Zimmermann <tzimmermann@suse.de>
Closes: https://lore.kernel.org/dri-devel/ba1bdfb8-dbf7-4372-bdcb-df7e0511c702@suse.de/
Cc: Shixiong Ou <oushixiong@kylinos.cn>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Link: https://lore.kernel.org/dri-devel/9792c6c3-a2b8-4b2b-b5ba-fba19b153e21@suse.de/ # [1]
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://lore.kernel.org/r/20250821064031.39090-1-tzimmermann@suse.de
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.