[Intel-gfx] [PATCH v9 08/32] drm: i915: fix common struct sg_table related issues

[Intel-gfx] [PATCH v9 08/32] drm: i915: fix common struct sg_table related issues

[Marek Szyprowski]

The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
returns the number of the created entries in the DMA address space.
However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
dma_unmap_sg must be called with the original number of the entries
passed to the dma_map_sg().

struct sg_table is a common structure used for describing a non-contiguous
memory buffer, used commonly in the DRM and graphics subsystems. It
consists of a scatterlist with memory pages and DMA addresses (sgl entry),
as well as the number of scatterlist entries: CPU pages (orig_nents entry)
and DMA mapped pages (nents entry).

It turned out that it was a common mistake to misuse nents and orig_nents
entries, calling DMA-mapping functions with a wrong number of entries or
ignoring the number of mapped entries returned by the dma_map_sg()
function.

This driver creatively uses sg_table->orig_nents to store the size of the
allocated scatterlist and ignores the number of the entries returned by
dma_map_sg function. The sg_table->orig_nents is (mis)used to properly
free the (over)allocated scatterlist.

This patch only introduces the common DMA-mapping wrappers operating
directly on the struct sg_table objects to the dmabuf related functions,
so the other drivers, which might share buffers with i915 could rely on
the properly set nents and orig_nents values.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c       | 11 +++--------
 drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c |  7 +++----
 2 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index 2679380159fc..8a988592715b 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
@@ -48,12 +48,9 @@ static struct sg_table *i915_gem_map_dma_buf(struct dma_buf_attachment *attachme
 		src = sg_next(src);
 	}
 
-	if (!dma_map_sg_attrs(attachment->dev,
-			      st->sgl, st->nents, dir,
-			      DMA_ATTR_SKIP_CPU_SYNC)) {
-		ret = -ENOMEM;
+	ret = dma_map_sgtable(attachment->dev, st, dir, DMA_ATTR_SKIP_CPU_SYNC);
+	if (ret)
 		goto err_free_sg;
-	}
 
 	return st;
 
@@ -73,9 +70,7 @@ static void i915_gem_unmap_dma_buf(struct dma_buf_attachment *attachment,
 {
 	struct drm_i915_gem_object *obj = dma_buf_to_obj(attachment->dmabuf);
 
-	dma_unmap_sg_attrs(attachment->dev,
-			   sg->sgl, sg->nents, dir,
-			   DMA_ATTR_SKIP_CPU_SYNC);
+	dma_unmap_sgtable(attachment->dev, sg, dir, DMA_ATTR_SKIP_CPU_SYNC);
 	sg_free_table(sg);
 	kfree(sg);
 
diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
index debaf7b18ab5..be30b27e2926 100644
--- a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
@@ -28,10 +28,9 @@ static struct sg_table *mock_map_dma_buf(struct dma_buf_attachment *attachment,
 		sg = sg_next(sg);
 	}
 
-	if (!dma_map_sg(attachment->dev, st->sgl, st->nents, dir)) {
-		err = -ENOMEM;
+	err = dma_map_sgtable(attachment->dev, st, dir, 0);
+	if (err)
 		goto err_st;
-	}
 
 	return st;
 
@@ -46,7 +45,7 @@ static void mock_unmap_dma_buf(struct dma_buf_attachment *attachment,
 			       struct sg_table *st,
 			       enum dma_data_direction dir)
 {
-	dma_unmap_sg(attachment->dev, st->sgl, st->nents, dir);
+	dma_unmap_sgtable(attachment->dev, st, dir, 0);
 	sg_free_table(st);
 	kfree(st);
 }
-- 
2.17.1

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Re: [Intel-gfx] [PATCH v9 08/32] drm: i915: fix common struct sg_table related issues

[Robin Murphy]

On 2020-08-26 07:32, Marek Szyprowski wrote:
> The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
> returns the number of the created entries in the DMA address space.
> However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
> dma_unmap_sg must be called with the original number of the entries
> passed to the dma_map_sg().
> 
> struct sg_table is a common structure used for describing a non-contiguous
> memory buffer, used commonly in the DRM and graphics subsystems. It
> consists of a scatterlist with memory pages and DMA addresses (sgl entry),
> as well as the number of scatterlist entries: CPU pages (orig_nents entry)
> and DMA mapped pages (nents entry).
> 
> It turned out that it was a common mistake to misuse nents and orig_nents
> entries, calling DMA-mapping functions with a wrong number of entries or
> ignoring the number of mapped entries returned by the dma_map_sg()
> function.
> 
> This driver creatively uses sg_table->orig_nents to store the size of the
> allocated scatterlist and ignores the number of the entries returned by
> dma_map_sg function. The sg_table->orig_nents is (mis)used to properly
> free the (over)allocated scatterlist.
> 
> This patch only introduces the common DMA-mapping wrappers operating
> directly on the struct sg_table objects to the dmabuf related functions,
> so the other drivers, which might share buffers with i915 could rely on
> the properly set nents and orig_nents values.

This one looks mechanical enough :)

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c       | 11 +++--------
>   drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c |  7 +++----
>   2 files changed, 6 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> index 2679380159fc..8a988592715b 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> @@ -48,12 +48,9 @@ static struct sg_table *i915_gem_map_dma_buf(struct dma_buf_attachment *attachme
>   		src = sg_next(src);
>   	}
>   
> -	if (!dma_map_sg_attrs(attachment->dev,
> -			      st->sgl, st->nents, dir,
> -			      DMA_ATTR_SKIP_CPU_SYNC)) {
> -		ret = -ENOMEM;
> +	ret = dma_map_sgtable(attachment->dev, st, dir, DMA_ATTR_SKIP_CPU_SYNC);
> +	if (ret)
>   		goto err_free_sg;
> -	}
>   
>   	return st;
>   
> @@ -73,9 +70,7 @@ static void i915_gem_unmap_dma_buf(struct dma_buf_attachment *attachment,
>   {
>   	struct drm_i915_gem_object *obj = dma_buf_to_obj(attachment->dmabuf);
>   
> -	dma_unmap_sg_attrs(attachment->dev,
> -			   sg->sgl, sg->nents, dir,
> -			   DMA_ATTR_SKIP_CPU_SYNC);
> +	dma_unmap_sgtable(attachment->dev, sg, dir, DMA_ATTR_SKIP_CPU_SYNC);
>   	sg_free_table(sg);
>   	kfree(sg);
>   
> diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
> index debaf7b18ab5..be30b27e2926 100644
> --- a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
> +++ b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
> @@ -28,10 +28,9 @@ static struct sg_table *mock_map_dma_buf(struct dma_buf_attachment *attachment,
>   		sg = sg_next(sg);
>   	}
>   
> -	if (!dma_map_sg(attachment->dev, st->sgl, st->nents, dir)) {
> -		err = -ENOMEM;
> +	err = dma_map_sgtable(attachment->dev, st, dir, 0);
> +	if (err)
>   		goto err_st;
> -	}
>   
>   	return st;
>   
> @@ -46,7 +45,7 @@ static void mock_unmap_dma_buf(struct dma_buf_attachment *attachment,
>   			       struct sg_table *st,
>   			       enum dma_data_direction dir)
>   {
> -	dma_unmap_sg(attachment->dev, st->sgl, st->nents, dir);
> +	dma_unmap_sgtable(attachment->dev, st, dir, 0);
>   	sg_free_table(st);
>   	kfree(st);
>   }
> 
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Re: [Intel-gfx] [PATCH v9 08/32] drm: i915: fix common struct sg_table related issues

[Ruhl, Michael J]

>-----Original Message-----
>From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of
>Marek Szyprowski
>Sent: Wednesday, August 26, 2020 2:33 AM
>To: dri-devel@lists.freedesktop.org; iommu@lists.linux-foundation.org;
>linaro-mm-sig@lists.linaro.org; linux-kernel@vger.kernel.org
>Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>; David Airlie
><airlied@linux.ie>; intel-gfx@lists.freedesktop.org; Robin Murphy
><robin.murphy@arm.com>; Christoph Hellwig <hch@lst.de>; linux-arm-
>kernel@lists.infradead.org; Marek Szyprowski
><m.szyprowski@samsung.com>
>Subject: [Intel-gfx] [PATCH v9 08/32] drm: i915: fix common struct sg_table
>related issues
>
>The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg()
>function
>returns the number of the created entries in the DMA address space.
>However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
>dma_unmap_sg must be called with the original number of the entries
>passed to the dma_map_sg().
>
>struct sg_table is a common structure used for describing a non-contiguous
>memory buffer, used commonly in the DRM and graphics subsystems. It
>consists of a scatterlist with memory pages and DMA addresses (sgl entry),
>as well as the number of scatterlist entries: CPU pages (orig_nents entry)
>and DMA mapped pages (nents entry).
>
>It turned out that it was a common mistake to misuse nents and orig_nents
>entries, calling DMA-mapping functions with a wrong number of entries or
>ignoring the number of mapped entries returned by the dma_map_sg()
>function.
>
>This driver creatively uses sg_table->orig_nents to store the size of the
>allocated scatterlist and ignores the number of the entries returned by
>dma_map_sg function. The sg_table->orig_nents is (mis)used to properly
>free the (over)allocated scatterlist.
>
>This patch only introduces the common DMA-mapping wrappers operating
>directly on the struct sg_table objects to the dmabuf related functions,
>so the other drivers, which might share buffers with i915 could rely on
>the properly set nents and orig_nents values.
>
>Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
>---
> drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c       | 11 +++--------
> drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c |  7 +++----
> 2 files changed, 6 insertions(+), 12 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>index 2679380159fc..8a988592715b 100644
>--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>@@ -48,12 +48,9 @@ static struct sg_table *i915_gem_map_dma_buf(struct
>dma_buf_attachment *attachme
> 		src = sg_next(src);
> 	}
>
>-	if (!dma_map_sg_attrs(attachment->dev,
>-			      st->sgl, st->nents, dir,
>-			      DMA_ATTR_SKIP_CPU_SYNC)) {
>-		ret = -ENOMEM;

You have dropped this error value.

Do you now if this is a benign loss?

M

>+	ret = dma_map_sgtable(attachment->dev, st, dir,
>DMA_ATTR_SKIP_CPU_SYNC);
>+	if (ret)
> 		goto err_free_sg;
>-	}
>
> 	return st;
>
>@@ -73,9 +70,7 @@ static void i915_gem_unmap_dma_buf(struct
>dma_buf_attachment *attachment,
> {
> 	struct drm_i915_gem_object *obj = dma_buf_to_obj(attachment-
>>dmabuf);
>
>-	dma_unmap_sg_attrs(attachment->dev,
>-			   sg->sgl, sg->nents, dir,
>-			   DMA_ATTR_SKIP_CPU_SYNC);
>+	dma_unmap_sgtable(attachment->dev, sg, dir,
>DMA_ATTR_SKIP_CPU_SYNC);
> 	sg_free_table(sg);
> 	kfree(sg);
>
>diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>index debaf7b18ab5..be30b27e2926 100644
>--- a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>+++ b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>@@ -28,10 +28,9 @@ static struct sg_table *mock_map_dma_buf(struct
>dma_buf_attachment *attachment,
> 		sg = sg_next(sg);
> 	}
>
>-	if (!dma_map_sg(attachment->dev, st->sgl, st->nents, dir)) {
>-		err = -ENOMEM;
>+	err = dma_map_sgtable(attachment->dev, st, dir, 0);
>+	if (err)
> 		goto err_st;
>-	}
>
> 	return st;
>
>@@ -46,7 +45,7 @@ static void mock_unmap_dma_buf(struct
>dma_buf_attachment *attachment,
> 			       struct sg_table *st,
> 			       enum dma_data_direction dir)
> {
>-	dma_unmap_sg(attachment->dev, st->sgl, st->nents, dir);
>+	dma_unmap_sgtable(attachment->dev, st, dir, 0);
> 	sg_free_table(st);
> 	kfree(st);
> }
>--
>2.17.1
>
>_______________________________________________
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>Intel-gfx@lists.freedesktop.org
>https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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Re: [Intel-gfx] [PATCH v9 08/32] drm: i915: fix common struct sg_table related issues

[Robin Murphy]

On 2020-09-01 20:38, Ruhl, Michael J wrote:
>> -----Original Message-----
>> From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of
>> Marek Szyprowski
>> Sent: Wednesday, August 26, 2020 2:33 AM
>> To: dri-devel@lists.freedesktop.org; iommu@lists.linux-foundation.org;
>> linaro-mm-sig@lists.linaro.org; linux-kernel@vger.kernel.org
>> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>; David Airlie
>> <airlied@linux.ie>; intel-gfx@lists.freedesktop.org; Robin Murphy
>> <robin.murphy@arm.com>; Christoph Hellwig <hch@lst.de>; linux-arm-
>> kernel@lists.infradead.org; Marek Szyprowski
>> <m.szyprowski@samsung.com>
>> Subject: [Intel-gfx] [PATCH v9 08/32] drm: i915: fix common struct sg_table
>> related issues
>>
>> The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg()
>> function
>> returns the number of the created entries in the DMA address space.
>> However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
>> dma_unmap_sg must be called with the original number of the entries
>> passed to the dma_map_sg().
>>
>> struct sg_table is a common structure used for describing a non-contiguous
>> memory buffer, used commonly in the DRM and graphics subsystems. It
>> consists of a scatterlist with memory pages and DMA addresses (sgl entry),
>> as well as the number of scatterlist entries: CPU pages (orig_nents entry)
>> and DMA mapped pages (nents entry).
>>
>> It turned out that it was a common mistake to misuse nents and orig_nents
>> entries, calling DMA-mapping functions with a wrong number of entries or
>> ignoring the number of mapped entries returned by the dma_map_sg()
>> function.
>>
>> This driver creatively uses sg_table->orig_nents to store the size of the
>> allocated scatterlist and ignores the number of the entries returned by
>> dma_map_sg function. The sg_table->orig_nents is (mis)used to properly
>> free the (over)allocated scatterlist.
>>
>> This patch only introduces the common DMA-mapping wrappers operating
>> directly on the struct sg_table objects to the dmabuf related functions,
>> so the other drivers, which might share buffers with i915 could rely on
>> the properly set nents and orig_nents values.
>>
>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
>> ---
>> drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c       | 11 +++--------
>> drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c |  7 +++----
>> 2 files changed, 6 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>> b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>> index 2679380159fc..8a988592715b 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>> @@ -48,12 +48,9 @@ static struct sg_table *i915_gem_map_dma_buf(struct
>> dma_buf_attachment *attachme
>> 		src = sg_next(src);
>> 	}
>>
>> -	if (!dma_map_sg_attrs(attachment->dev,
>> -			      st->sgl, st->nents, dir,
>> -			      DMA_ATTR_SKIP_CPU_SYNC)) {
>> -		ret = -ENOMEM;
> 
> You have dropped this error value.
> 
> Do you now if this is a benign loss?

True, dma_map_sgtable() will return -EINVAL rather than -ENOMEM for 
failure. A quick look through other .map_dma_buf callbacks suggests 
they're returning a motley mix of error values and NULL for failure 
cases, so I'd imagine that importers shouldn't be too sensitive to the 
exact value.

Robin.

> 
> M
> 
>> +	ret = dma_map_sgtable(attachment->dev, st, dir,
>> DMA_ATTR_SKIP_CPU_SYNC);
>> +	if (ret)
>> 		goto err_free_sg;
>> -	}
>>
>> 	return st;
>>
>> @@ -73,9 +70,7 @@ static void i915_gem_unmap_dma_buf(struct
>> dma_buf_attachment *attachment,
>> {
>> 	struct drm_i915_gem_object *obj = dma_buf_to_obj(attachment-
>>> dmabuf);
>>
>> -	dma_unmap_sg_attrs(attachment->dev,
>> -			   sg->sgl, sg->nents, dir,
>> -			   DMA_ATTR_SKIP_CPU_SYNC);
>> +	dma_unmap_sgtable(attachment->dev, sg, dir,
>> DMA_ATTR_SKIP_CPU_SYNC);
>> 	sg_free_table(sg);
>> 	kfree(sg);
>>
>> diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>> b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>> index debaf7b18ab5..be30b27e2926 100644
>> --- a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>> +++ b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>> @@ -28,10 +28,9 @@ static struct sg_table *mock_map_dma_buf(struct
>> dma_buf_attachment *attachment,
>> 		sg = sg_next(sg);
>> 	}
>>
>> -	if (!dma_map_sg(attachment->dev, st->sgl, st->nents, dir)) {
>> -		err = -ENOMEM;
>> +	err = dma_map_sgtable(attachment->dev, st, dir, 0);
>> +	if (err)
>> 		goto err_st;
>> -	}
>>
>> 	return st;
>>
>> @@ -46,7 +45,7 @@ static void mock_unmap_dma_buf(struct
>> dma_buf_attachment *attachment,
>> 			       struct sg_table *st,
>> 			       enum dma_data_direction dir)
>> {
>> -	dma_unmap_sg(attachment->dev, st->sgl, st->nents, dir);
>> +	dma_unmap_sgtable(attachment->dev, st, dir, 0);
>> 	sg_free_table(st);
>> 	kfree(st);
>> }
>> --
>> 2.17.1
>>
>> _______________________________________________
>> Intel-gfx mailing list
>> Intel-gfx@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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Re: [Intel-gfx] [PATCH v9 08/32] drm: i915: fix common struct sg_table related issues

[Ruhl, Michael J]

>-----Original Message-----
>From: Robin Murphy <robin.murphy@arm.com>
>Sent: Tuesday, September 1, 2020 3:54 PM
>To: Ruhl, Michael J <michael.j.ruhl@intel.com>; Marek Szyprowski
><m.szyprowski@samsung.com>; dri-devel@lists.freedesktop.org;
>iommu@lists.linux-foundation.org; linaro-mm-sig@lists.linaro.org; linux-
>kernel@vger.kernel.org
>Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>; David Airlie
><airlied@linux.ie>; intel-gfx@lists.freedesktop.org; Christoph Hellwig
><hch@lst.de>; linux-arm-kernel@lists.infradead.org
>Subject: Re: [Intel-gfx] [PATCH v9 08/32] drm: i915: fix common struct
>sg_table related issues
>
>On 2020-09-01 20:38, Ruhl, Michael J wrote:
>>> -----Original Message-----
>>> From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of
>>> Marek Szyprowski
>>> Sent: Wednesday, August 26, 2020 2:33 AM
>>> To: dri-devel@lists.freedesktop.org; iommu@lists.linux-foundation.org;
>>> linaro-mm-sig@lists.linaro.org; linux-kernel@vger.kernel.org
>>> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>; David Airlie
>>> <airlied@linux.ie>; intel-gfx@lists.freedesktop.org; Robin Murphy
>>> <robin.murphy@arm.com>; Christoph Hellwig <hch@lst.de>; linux-arm-
>>> kernel@lists.infradead.org; Marek Szyprowski
>>> <m.szyprowski@samsung.com>
>>> Subject: [Intel-gfx] [PATCH v9 08/32] drm: i915: fix common struct sg_table
>>> related issues
>>>
>>> The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg()
>>> function
>>> returns the number of the created entries in the DMA address space.
>>> However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
>>> dma_unmap_sg must be called with the original number of the entries
>>> passed to the dma_map_sg().
>>>
>>> struct sg_table is a common structure used for describing a non-contiguous
>>> memory buffer, used commonly in the DRM and graphics subsystems. It
>>> consists of a scatterlist with memory pages and DMA addresses (sgl entry),
>>> as well as the number of scatterlist entries: CPU pages (orig_nents entry)
>>> and DMA mapped pages (nents entry).
>>>
>>> It turned out that it was a common mistake to misuse nents and orig_nents
>>> entries, calling DMA-mapping functions with a wrong number of entries or
>>> ignoring the number of mapped entries returned by the dma_map_sg()
>>> function.
>>>
>>> This driver creatively uses sg_table->orig_nents to store the size of the
>>> allocated scatterlist and ignores the number of the entries returned by
>>> dma_map_sg function. The sg_table->orig_nents is (mis)used to properly
>>> free the (over)allocated scatterlist.
>>>
>>> This patch only introduces the common DMA-mapping wrappers operating
>>> directly on the struct sg_table objects to the dmabuf related functions,
>>> so the other drivers, which might share buffers with i915 could rely on
>>> the properly set nents and orig_nents values.
>>>
>>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
>>> ---
>>> drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c       | 11 +++--------
>>> drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c |  7 +++----
>>> 2 files changed, 6 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>>> b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>>> index 2679380159fc..8a988592715b 100644
>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
>>> @@ -48,12 +48,9 @@ static struct sg_table
>*i915_gem_map_dma_buf(struct
>>> dma_buf_attachment *attachme
>>> 		src = sg_next(src);
>>> 	}
>>>
>>> -	if (!dma_map_sg_attrs(attachment->dev,
>>> -			      st->sgl, st->nents, dir,
>>> -			      DMA_ATTR_SKIP_CPU_SYNC)) {
>>> -		ret = -ENOMEM;
>>
>> You have dropped this error value.
>>
>> Do you now if this is a benign loss?
>
>True, dma_map_sgtable() will return -EINVAL rather than -ENOMEM for
>failure. A quick look through other .map_dma_buf callbacks suggests
>they're returning a motley mix of error values and NULL for failure
>cases, so I'd imagine that importers shouldn't be too sensitive to the
>exact value.

I followed some of our code through to see if anyone is checking for -ENOMEM...

I have found in some test paths... However, it is not clear to me if we can get
to those paths from here.

Anyways,

Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>

Mike

>Robin.
>
>>
>> M
>>
>>> +	ret = dma_map_sgtable(attachment->dev, st, dir,
>>> DMA_ATTR_SKIP_CPU_SYNC);
>>> +	if (ret)
>>> 		goto err_free_sg;
>>> -	}
>>>
>>> 	return st;
>>>
>>> @@ -73,9 +70,7 @@ static void i915_gem_unmap_dma_buf(struct
>>> dma_buf_attachment *attachment,
>>> {
>>> 	struct drm_i915_gem_object *obj = dma_buf_to_obj(attachment-
>>>> dmabuf);
>>>
>>> -	dma_unmap_sg_attrs(attachment->dev,
>>> -			   sg->sgl, sg->nents, dir,
>>> -			   DMA_ATTR_SKIP_CPU_SYNC);
>>> +	dma_unmap_sgtable(attachment->dev, sg, dir,
>>> DMA_ATTR_SKIP_CPU_SYNC);
>>> 	sg_free_table(sg);
>>> 	kfree(sg);
>>>
>>> diff --git a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>>> b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>>> index debaf7b18ab5..be30b27e2926 100644
>>> --- a/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>>> +++ b/drivers/gpu/drm/i915/gem/selftests/mock_dmabuf.c
>>> @@ -28,10 +28,9 @@ static struct sg_table *mock_map_dma_buf(struct
>>> dma_buf_attachment *attachment,
>>> 		sg = sg_next(sg);
>>> 	}
>>>
>>> -	if (!dma_map_sg(attachment->dev, st->sgl, st->nents, dir)) {
>>> -		err = -ENOMEM;
>>> +	err = dma_map_sgtable(attachment->dev, st, dir, 0);
>>> +	if (err)
>>> 		goto err_st;
>>> -	}
>>>
>>> 	return st;
>>>
>>> @@ -46,7 +45,7 @@ static void mock_unmap_dma_buf(struct
>>> dma_buf_attachment *attachment,
>>> 			       struct sg_table *st,
>>> 			       enum dma_data_direction dir)
>>> {
>>> -	dma_unmap_sg(attachment->dev, st->sgl, st->nents, dir);
>>> +	dma_unmap_sgtable(attachment->dev, st, dir, 0);
>>> 	sg_free_table(st);
>>> 	kfree(st);
>>> }
>>> --
>>> 2.17.1
>>>
>>> _______________________________________________
>>> Intel-gfx mailing list
>>> Intel-gfx@lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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