linux/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c, branch v6.17

drm/amdgpu: Pin buffers while vmap'ing exported dma-buf objects

2025-08-22T12:05:31Z

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] [ 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 Fixes: 660cd44659a0 ("drm/shmem-helper: Import dmabuf without mapping its sg_table") Reported-by: Thomas Zimmermann Closes: https://lore.kernel.org/dri-devel/ba1bdfb8-dbf7-4372-bdcb-df7e0511c702@suse.de/ Cc: Shixiong Ou Cc: Thomas Zimmermann Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: David Airlie Cc: Simona Vetter Cc: Sumit Semwal Cc: "Christian König" 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 Link: https://lore.kernel.org/r/20250821064031.39090-1-tzimmermann@suse.de

Revert "drm/amdgpu: Use dma_buf from GEM object instance"

2025-08-13T09:14:17Z

This reverts commit 515986100d176663d0a03219a3056e4252f729e6. The dma_buf field in struct drm_gem_object is not stable over the object instance's lifetime. The field becomes NULL when user space releases the final GEM handle on the buffer object. This resulted in a NULL-pointer deref. Workarounds in commit 5307dce878d4 ("drm/gem: Acquire references on GEM handles for framebuffers") and commit f6bfc9afc751 ("drm/framebuffer: Acquire internal references on GEM handles") only solved the problem partially. They especially don't work for buffer objects without a DRM framebuffer associated. Hence, this revert to going back to using .import_attach->dmabuf. Signed-off-by: Thomas Zimmermann Reviewed-by: Simona Vetter Acked-by: Alex Deucher Link: https://lore.kernel.org/r/20250715082635.34974-1-tzimmermann@suse.de

drm/amdgpu: Use dma_buf from GEM object instance

2025-06-30T15:55:16Z

Avoid dereferencing struct drm_gem_object.import_attach for the imported dma-buf. The dma_buf field in the GEM object instance refers to the same buffer. Prepares to make import_attach an implementation detail of PRIME. Reviewed-by: Christian König Signed-off-by: Thomas Zimmermann Signed-off-by: Alex Deucher

drm/amdgpu: Test for imported buffers with drm_gem_is_imported()

2025-06-30T15:54:59Z

Instead of testing import_attach for imported GEM buffers, invoke drm_gem_is_imported() to do the test. v2: - keep amdgpu_bo_print_info() as-is (Christian) Reviewed-by: Christian König Signed-off-by: Thomas Zimmermann Signed-off-by: Alex Deucher

drm/amdgpu: Fail DMABUF map of XGMI-accessible memory

2025-05-01T15:01:46Z

If peer memory is XGMI-accessible, we should never access it through PCIe P2P DMA mappings. PCIe P2P is slower, has different coherence behaviour, limited or no support for atomics, or may not work at all. Fail with a warning if DMABUF mappings of such memory are attempted. Signed-off-by: Felix Kuehling Reviewed-by: Christian König Signed-off-by: Alex Deucher (cherry picked from commit dbe4c63689bc6b5fd3ab72650ea4b6a667e96a68)

drm/amdgpu: Allow P2P access through XGMI

2025-04-22T20:47:12Z

If peer memory is accessible through XGMI, allow leaving it in VRAM rather than forcing its migration to GTT on DMABuf attachment. Signed-off-by: Felix Kuehling Tested-by: Hao (Claire) Zhou Reviewed-by: Christian König Signed-off-by: Alex Deucher (cherry picked from commit 372c8d72c3680fdea3fbb2d6b089f76b4a6d596a)

drm/amdgpu: Don't pin VRAM without DMABUF_MOVE_NOTIFY

2025-04-22T20:44:28Z

Pinning of VRAM is for peer devices that don't support dynamic attachment and move notifiers. But it requires that all such peer devices are able to access VRAM via PCIe P2P. Any device without P2P access requires migration to GTT, which fails if the memory is already pinned for another peer device. Sharing between GPUs should not require pinning in VRAM. However, if DMABUF_MOVE_NOTIFY is disabled in the kernel build, even DMABufs shared between GPUs must be pinned, which can lead to failures and functional regressions on systems where some peer GPUs are not P2P accessible. Disable VRAM pinning if move notifiers are disabled in the kernel build to fix regressions when sharing BOs between GPUs. Signed-off-by: Felix Kuehling Tested-by: Hao (Claire) Zhou Reviewed-by: Christian König Signed-off-by: Alex Deucher (cherry picked from commit 05185812ae3695fe049c14847ce3cbeccff1bf2e)

drm/amdgpu: Use allowed_domains for pinning dmabufs

2025-04-22T20:44:02Z

When determining the domains for pinning DMABufs, filter allowed_domains and fail with a warning if VRAM is forbidden and GTT is not an allowed domain. Fixes: f5e7fabd1f5c ("drm/amdgpu: allow pinning DMA-bufs into VRAM if all importers can do P2P") Suggested-by: Christian König Signed-off-by: Felix Kuehling Reviewed-by: Christian König Signed-off-by: Alex Deucher (cherry picked from commit 3940796a6eefa555fec688a4adee5659ef9fa431)

drm/amdgpu: allow pinning DMA-bufs into VRAM if all importers can do P2P

2025-04-07T19:18:30Z

Try pinning into VRAM to allow P2P with RDMA NICs without ODP support if all attachments can do P2P. If any attachment can't do P2P just pin into GTT instead. Acked-by: Simona Vetter Signed-off-by: Christian König Signed-off-by: Felix Kuehling Reviewed-by: Felix Kuehling Tested-by: Pak Nin Lui Cc: Simona Vetter Signed-off-by: Alex Deucher

drm/amdgpu/dma_buf: fix page_link check

2025-04-07T18:31:45Z

The page_link lower bits of the first sg could contain something like SG_END, if we are mapping a single VRAM page or contiguous blob which fits into one sg entry. Rather pull out the struct page, and use that in our check to know if we mapped struct pages vs VRAM. Fixes: f44ffd677fb3 ("drm/amdgpu: add support for exporting VRAM using DMA-buf v3") Signed-off-by: Matthew Auld Cc: Christian König Cc: amd-gfx@lists.freedesktop.org Cc: # v5.8+ Reviewed-by: Christian König Signed-off-by: Alex Deucher