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From:   Marek Szyprowski <m.szyprowski@samsung.com>
To:     dri-devel@lists.freedesktop.org, iommu@lists.linux-foundation.org,
        linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@samsung.com>,
        Christoph Hellwig <hch@lst.de>,
        Robin Murphy <robin.murphy@arm.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        linux-arm-kernel@lists.infradead.org,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Gerd Hoffmann <kraxel@redhat.com>,
        virtualization@lists.linux-foundation.org
Subject: [PATCH v2 13/21] drm: virtio: fix sg_table nents vs. orig_nents
 misuse
Date:   Mon,  4 May 2020 14:53:51 +0200
Message-Id: <20200504125359.5678-13-m.szyprowski@samsung.com>
In-Reply-To: <20200504125359.5678-1-m.szyprowski@samsung.com>
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References: <20200504125017.5494-1-m.szyprowski@samsung.com>
        <20200504125359.5678-1-m.szyprowski@samsung.com>
        <CGME20200504125418eucas1p190ccb7626f969de8c6d53d216ea12a96@eucas1p1.samsung.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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/virtio/virtgpu_object.c | 11 ++++++-----
 drivers/gpu/drm/virtio/virtgpu_vq.c     |  8 ++++----
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
index 6ccbd01..12f6bee 100644
--- a/drivers/gpu/drm/virtio/virtgpu_object.c
+++ b/drivers/gpu/drm/virtio/virtgpu_object.c
@@ -73,7 +73,8 @@ void virtio_gpu_cleanup_object(struct virtio_gpu_object *bo)
 		if (shmem->pages) {
 			if (shmem->mapped) {
 				dma_unmap_sg(vgdev->vdev->dev.parent,
-					     shmem->pages->sgl, shmem->mapped,
+					     shmem->pages->sgl,
+					     shmem->pages->orig_nents,
 					     DMA_TO_DEVICE);
 				shmem->mapped = 0;
 			}
@@ -157,13 +158,13 @@ static int virtio_gpu_object_shmem_init(struct virtio_gpu_device *vgdev,
 	}
 
 	if (use_dma_api) {
-		shmem->mapped = dma_map_sg(vgdev->vdev->dev.parent,
+		shmem->pages->nents = dma_map_sg(vgdev->vdev->dev.parent,
 					   shmem->pages->sgl,
-					   shmem->pages->nents,
+					   shmem->pages->orig_nents,
 					   DMA_TO_DEVICE);
-		*nents = shmem->mapped;
+		*nents = shmem->mapped = shmem->pages->nents;
 	} else {
-		*nents = shmem->pages->nents;
+		*nents = shmem->pages->orig_nents;
 	}
 
 	*ents = kmalloc_array(*nents, sizeof(struct virtio_gpu_mem_entry),
diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index 9e663a5..661325b 100644
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -604,8 +604,8 @@ void virtio_gpu_cmd_transfer_to_host_2d(struct virtio_gpu_device *vgdev,
 
 	if (use_dma_api)
 		dma_sync_sg_for_device(vgdev->vdev->dev.parent,
-				       shmem->pages->sgl, shmem->pages->nents,
-				       DMA_TO_DEVICE);
+				       shmem->pages->sgl,
+				       shmem->pages->orig_nents, DMA_TO_DEVICE);
 
 	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
 	memset(cmd_p, 0, sizeof(*cmd_p));
@@ -1020,8 +1020,8 @@ void virtio_gpu_cmd_transfer_to_host_3d(struct virtio_gpu_device *vgdev,
 
 	if (use_dma_api)
 		dma_sync_sg_for_device(vgdev->vdev->dev.parent,
-				       shmem->pages->sgl, shmem->pages->nents,
-				       DMA_TO_DEVICE);
+				       shmem->pages->sgl,
+				       shmem->pages->orig_nents, DMA_TO_DEVICE);
 
 	cmd_p = virtio_gpu_alloc_cmd(vgdev, &vbuf, sizeof(*cmd_p));
 	memset(cmd_p, 0, sizeof(*cmd_p));
-- 
1.9.1