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.szyprow...@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

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