[v2,09/21] drm: panfrost: fix sg_table nents vs. orig_nents misuse

Message ID 20200504125359.5678-9-m.szyprowski@samsung.com
State New
Headers show
Series
  • DRM: fix struct sg_table nents vs. orig_nents misuse
Related show

Commit Message

Marek Szyprowski May 4, 2020, 12:53 p.m.
The Documentation/DMA-API-HOWTO.txt states that dma_map_sg returns the
numer of the created entries in the DMA address space. However the
subsequent calls to dma_sync_sg_for_{device,cpu} and dma_unmap_sg must be
called with the original number of entries passed to dma_map_sg. The
sg_table->nents in turn holds the result of the dma_map_sg call as stated
in include/linux/scatterlist.h. Adapt the code to obey those rules.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

---
For more information, see '[PATCH v2 00/21] DRM: fix struct sg_table nents
vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/4/373
---
 drivers/gpu/drm/panfrost/panfrost_gem.c | 3 ++-
 drivers/gpu/drm/panfrost/panfrost_mmu.c | 4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)

-- 
1.9.1

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Comments

Steven Price May 4, 2020, 1:27 p.m. | #1
On 04/05/2020 13:53, Marek Szyprowski wrote:
> The Documentation/DMA-API-HOWTO.txt states that dma_map_sg returns the

> numer of the created entries in the DMA address space. However the

> subsequent calls to dma_sync_sg_for_{device,cpu} and dma_unmap_sg must be

> called with the original number of entries passed to dma_map_sg. The

> sg_table->nents in turn holds the result of the dma_map_sg call as stated

> in include/linux/scatterlist.h. Adapt the code to obey those rules.


I find this commit message a bit confusing, but AFAICT the problem with 
the Panfrost code is really in mmu_map_sg() where we don't have the 
return value from dma_map_sg() and the for_each_sg() loop could (in 
theory) run off the end of the list.

The fix seems correct - store the return where it's meant to be (nents) 
and make sure when unmapping we use the original (orig_nents). So you 
might also consider adding:

Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver")

Even better would be the wrappers you mention in the cover letter! ;)

Reviewed-by: Steven Price <steven.price@arm.com>


> 

> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

> ---

> For more information, see '[PATCH v2 00/21] DRM: fix struct sg_table nents

> vs. orig_nents misuse' thread: https://lkml.org/lkml/2020/5/4/373

> ---

>   drivers/gpu/drm/panfrost/panfrost_gem.c | 3 ++-

>   drivers/gpu/drm/panfrost/panfrost_mmu.c | 4 +++-

>   2 files changed, 5 insertions(+), 2 deletions(-)

> 

> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c

> index 17b654e..22fec7c 100644

> --- a/drivers/gpu/drm/panfrost/panfrost_gem.c

> +++ b/drivers/gpu/drm/panfrost/panfrost_gem.c

> @@ -42,7 +42,8 @@ static void panfrost_gem_free_object(struct drm_gem_object *obj)

>   		for (i = 0; i < n_sgt; i++) {

>   			if (bo->sgts[i].sgl) {

>   				dma_unmap_sg(pfdev->dev, bo->sgts[i].sgl,

> -					     bo->sgts[i].nents, DMA_BIDIRECTIONAL);

> +					     bo->sgts[i].orig_nents,

> +					     DMA_BIDIRECTIONAL);

>   				sg_free_table(&bo->sgts[i]);

>   			}

>   		}

> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c

> index ed28aeb..2d9b1f9 100644

> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c

> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c

> @@ -517,7 +517,9 @@ static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,

>   	if (ret)

>   		goto err_pages;

>   

> -	if (!dma_map_sg(pfdev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL)) {

> +	sgt->nents = dma_map_sg(pfdev->dev, sgt->sgl, sgt->orig_nents,

> +				DMA_BIDIRECTIONAL);

> +	if (!sgt->nents) {

>   		ret = -EINVAL;

>   		goto err_map;

>   	}

> 


_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

Patch

diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.c b/drivers/gpu/drm/panfrost/panfrost_gem.c
index 17b654e..22fec7c 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gem.c
+++ b/drivers/gpu/drm/panfrost/panfrost_gem.c
@@ -42,7 +42,8 @@  static void panfrost_gem_free_object(struct drm_gem_object *obj)
 		for (i = 0; i < n_sgt; i++) {
 			if (bo->sgts[i].sgl) {
 				dma_unmap_sg(pfdev->dev, bo->sgts[i].sgl,
-					     bo->sgts[i].nents, DMA_BIDIRECTIONAL);
+					     bo->sgts[i].orig_nents,
+					     DMA_BIDIRECTIONAL);
 				sg_free_table(&bo->sgts[i]);
 			}
 		}
diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c b/drivers/gpu/drm/panfrost/panfrost_mmu.c
index ed28aeb..2d9b1f9 100644
--- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
+++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
@@ -517,7 +517,9 @@  static int panfrost_mmu_map_fault_addr(struct panfrost_device *pfdev, int as,
 	if (ret)
 		goto err_pages;
 
-	if (!dma_map_sg(pfdev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL)) {
+	sgt->nents = dma_map_sg(pfdev->dev, sgt->sgl, sgt->orig_nents,
+				DMA_BIDIRECTIONAL);
+	if (!sgt->nents) {
 		ret = -EINVAL;
 		goto err_map;
 	}