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Reply-To: christian.koenig@amd.com
Subject: Re: [RFC 02/17] drm: amdgpu: fix sg_table nents vs. orig_nents misuse
To:     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:     Daniel Vetter <daniel@ffwll.ch>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        David Airlie <airlied@linux.ie>,
        intel-gfx@lists.freedesktop.org, amd-gfx@lists.freedesktop.org,
        Christoph Hellwig <hch@lst.de>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        linux-arm-kernel@lists.infradead.org
References: <20200428132005.21424-1-m.szyprowski@samsung.com>
 <CGME20200428132023eucas1p2a1993145eef91506698aa8c9750a7e43@eucas1p2.samsung.com>
 <20200428132005.21424-3-m.szyprowski@samsung.com>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <ckoenig.leichtzumerken@gmail.com>
Message-ID: <c462d1f0-8daa-76bb-a7fd-5e0d687975d5@gmail.com>
Date:   Tue, 28 Apr 2020 17:14:40 +0200
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Am 28.04.20 um 15:19 schrieb Marek Szyprowski:
> 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>

Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 7 ++++---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c     | 8 ++++----
>   2 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> index 43d8ed7..4df813e 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> @@ -307,8 +307,9 @@ static struct sg_table *amdgpu_dma_buf_map(struct dma_buf_attachment *attach,
>   		if (IS_ERR(sgt))
>   			return sgt;
>   
> -		if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
> -				      DMA_ATTR_SKIP_CPU_SYNC))
> +		sgt->nents = dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->orig_nents,
> +					      dir, DMA_ATTR_SKIP_CPU_SYNC);
> +		if (!sgt->nents)
>   			goto error_free;
>   		break;
>   
> @@ -349,7 +350,7 @@ static void amdgpu_dma_buf_unmap(struct dma_buf_attachment *attach,
>   	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
>   
>   	if (sgt->sgl->page_link) {
> -		dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents, dir);
> +		dma_unmap_sg(attach->dev, sgt->sgl, sgt->orig_nents, dir);
>   		sg_free_table(sgt);
>   		kfree(sgt);
>   	} else {
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index d5543c2..5f31585 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -1043,7 +1043,6 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_tt *ttm)
>   {
>   	struct amdgpu_device *adev = amdgpu_ttm_adev(ttm->bdev);
>   	struct amdgpu_ttm_tt *gtt = (void *)ttm;
> -	unsigned nents;
>   	int r;
>   
>   	int write = !(gtt->userflags & AMDGPU_GEM_USERPTR_READONLY);
> @@ -1059,8 +1058,9 @@ static int amdgpu_ttm_tt_pin_userptr(struct ttm_tt *ttm)
>   
>   	/* Map SG to device */
>   	r = -ENOMEM;
> -	nents = dma_map_sg(adev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
> -	if (nents == 0)
> +	ttm->sg->nents = dma_map_sg(adev->dev, ttm->sg->sgl,
> +				    ttm->sg->orig_nents, direction);
> +	if (ttm->sg->nents == 0)
>   		goto release_sg;
>   
>   	/* convert SG to linear array of pages and dma addresses */
> @@ -1091,7 +1091,7 @@ static void amdgpu_ttm_tt_unpin_userptr(struct ttm_tt *ttm)
>   		return;
>   
>   	/* unmap the pages mapped to the device */
> -	dma_unmap_sg(adev->dev, ttm->sg->sgl, ttm->sg->nents, direction);
> +	dma_unmap_sg(adev->dev, ttm->sg->sgl, ttm->sg->orig_nents, direction);
>   
>   	sg_free_table(ttm->sg);
>