linux-kernel - [RFC 13/17] drm: virtio: fix sg_table nents vs. orig

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Message-Id: <20200428132005.21424-14-m.szyprowski@samsung.com>
Date:   Tue, 28 Apr 2020 15:20:01 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     dri-devel@...ts.freedesktop.org, iommu@...ts.linux-foundation.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        intel-gfx@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        amd-gfx@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Subject: [RFC 13/17] drm: virtio: fix sg_table nents vs. orig_nents misuse

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@...sung.com>
---
 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