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Message-ID: <790da31e-b20c-4ad3-a534-de55cd741519@suse.de>
Date: Fri, 15 Aug 2025 08:02:27 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: sumit.semwal@...aro.org, christian.koenig@....com, oushixiong@...inos.cn,
maarten.lankhorst@...ux.intel.com, mripard@...nel.org, airlied@...il.com,
simona@...ll.ch
Cc: dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/gem-shmem: Pin and unpin buffers when importing w/o
S/G table
FYI this patch got feedback at
https://lore.kernel.org/dri-devel/805acaca-3b91-438d-b842-25c055fd898c@amd.com/
Preferably the problem should be addressed on GEM/PRIME code instead of
dma-buf.
Best regards
Thomas
Am 14.08.25 um 09:34 schrieb Thomas Zimmermann:
> Imported dma-buf objects need to be pinned while being vmap'ed into
> kernel address space. This used to be done before while creating an
> S/G table.
>
> GEM-SHMEN can import dma-buf objects without creating the S/G table,
> but the pin/unpin is now missing. Leads to page-mapping 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]
>
> Support pin/unpin in drm_buf_map_attachment() without creating an S/G
> table. Passing DMA_NONE for the DMA direction will only pin. Do the
> inverse for unmap_attachment(). Modify GEM-SHMEM accordingly, so that
> it pins the imported dma-buf.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@...e.de>
> Fixes: 660cd44659a0 ("drm/shmem-helper: Import dmabuf without mapping its sg_table")
> Reported-by: Thomas Zimmermann <tzimmermann@...e.de>
> Closes: https://lore.kernel.org/dri-devel/ba1bdfb8-dbf7-4372-bdcb-df7e0511c702@suse.de/
> Cc: Shixiong Ou <oushixiong@...inos.cn>
> Cc: Thomas Zimmermann <tzimmermann@...e.de>
> Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
> Cc: Maxime Ripard <mripard@...nel.org>
> Cc: David Airlie <airlied@...il.com>
> Cc: Simona Vetter <simona@...ll.ch>
> Cc: Sumit Semwal <sumit.semwal@...aro.org>
> Cc: "Christian König" <christian.koenig@....com>
> Cc: dri-devel@...ts.freedesktop.org
> Cc: linux-media@...r.kernel.org
> Cc: linaro-mm-sig@...ts.linaro.org
> ---
> drivers/dma-buf/dma-buf.c | 16 +++++++++++++---
> drivers/gpu/drm/drm_gem_shmem_helper.c | 11 ++++++++++-
> drivers/gpu/drm/drm_prime.c | 2 ++
> 3 files changed, 25 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 2bcf9ceca997..f1e1385ce630 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -1086,7 +1086,8 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_unpin, "DMA_BUF");
> * @direction: [in] direction of DMA transfer
> *
> * Returns sg_table containing the scatterlist to be returned; returns ERR_PTR
> - * on error. May return -EINTR if it is interrupted by a signal.
> + * on error. May return -EINTR if it is interrupted by a signal. Returns NULL
> + * on success iff direction is DMA_NONE.
> *
> * On success, the DMA addresses and lengths in the returned scatterlist are
> * PAGE_SIZE aligned.
> @@ -1122,6 +1123,8 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
> if (ret)
> return ERR_PTR(ret);
> }
> + if (!valid_dma_direction(direction))
> + return NULL; /* only pin; don't map */
>
> sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
> if (!sg_table)
> @@ -1216,14 +1219,21 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> {
> might_sleep();
>
> - if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
> + if (WARN_ON(!attach || !attach->dmabuf))
> return;
>
> dma_resv_assert_held(attach->dmabuf->resv);
>
> + if (!valid_dma_direction(direction))
> + goto unpin;
> +
> + if (WARN_ON(!sg_table))
> + return;
> +
> mangle_sg_table(sg_table);
> attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
>
> +unpin:
> if (dma_buf_pin_on_map(attach))
> attach->dmabuf->ops->unpin(attach);
> }
> @@ -1245,7 +1255,7 @@ void dma_buf_unmap_attachment_unlocked(struct dma_buf_attachment *attach,
> {
> might_sleep();
>
> - if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
> + if (WARN_ON(!attach || !attach->dmabuf))
> return;
>
> dma_resv_lock(attach->dmabuf->resv, NULL);
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 5d1349c34afd..1b66501420d3 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -817,6 +817,7 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
> struct dma_buf *dma_buf)
> {
> struct dma_buf_attachment *attach;
> + struct sg_table *sgt;
> struct drm_gem_shmem_object *shmem;
> struct drm_gem_object *obj;
> size_t size;
> @@ -838,12 +839,18 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
>
> get_dma_buf(dma_buf);
>
> + sgt = dma_buf_map_attachment_unlocked(attach, DMA_NONE);
> + if (IS_ERR(sgt)) {
> + ret = PTR_ERR(sgt);
> + goto fail_detach;
> + }
> +
> size = PAGE_ALIGN(attach->dmabuf->size);
>
> shmem = __drm_gem_shmem_create(dev, size, true, NULL);
> if (IS_ERR(shmem)) {
> ret = PTR_ERR(shmem);
> - goto fail_detach;
> + goto fail_unmap;
> }
>
> drm_dbg_prime(dev, "size = %zu\n", size);
> @@ -853,6 +860,8 @@ struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
>
> return &shmem->base;
>
> +fail_unmap:
> + dma_buf_unmap_attachment_unlocked(attach, sgt, DMA_NONE);
> fail_detach:
> dma_buf_detach(dma_buf, attach);
> dma_buf_put(dma_buf);
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 43a10b4af43a..b3b070868e3b 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -1109,6 +1109,8 @@ void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *sg)
> attach = obj->import_attach;
> if (sg)
> dma_buf_unmap_attachment_unlocked(attach, sg, DMA_BIDIRECTIONAL);
> + else
> + dma_buf_unmap_attachment_unlocked(attach, NULL, DMA_NONE);
> dma_buf = attach->dmabuf;
> dma_buf_detach(attach->dmabuf, attach);
> /* remove the reference */
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
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