On 5/10/23 11:26, Xuan Zhuo wrote:
On Wed, 10 May 2023 10:54:37 +0800, zhenwei pi <pizhenwei@xxxxxxxxxxxxx> wrote:Both split ring and packed ring use 32bits to describe the length of a descriptor: see struct vring_desc and struct vring_packed_desc. This means the max segment size supported by virtio is U32_MAX. An example of virtio_max_dma_size in virtio_blk.c: u32 v, max_size; max_size = virtio_max_dma_size(vdev); -> implicit convert err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX, struct virtio_blk_config, size_max, &v); max_size = min(max_size, v); There is a risk during implicit convert here, once virtio_max_dma_size returns 4G, max_size becomes 0. Fixes: e6d6dd6c875e ("virtio: Introduce virtio_max_dma_size()") Cc: Joerg Roedel <jroedel@xxxxxxx> Signed-off-by: zhenwei pi <pizhenwei@xxxxxxxxxxxxx> --- drivers/virtio/virtio_ring.c | 12 ++++++++---- include/linux/virtio.h | 2 +- 2 files changed, 9 insertions(+), 5 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index c5310eaf8b46..55cfecf030a1 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -289,12 +289,16 @@ static bool vring_use_dma_api(const struct virtio_device *vdev) return false; } -size_t virtio_max_dma_size(const struct virtio_device *vdev) +u32 virtio_max_dma_size(const struct virtio_device *vdev)LGTM But, should we change the parameter to vq, then use the dma_dev? @Jason Thanks.
The max DMA size is a attribute of a virtio device rather than any VQ, so I guess virtio_max_dma_size(const struct virtio_device *vdev) is clear.
On the other hand, if changing the parameter to vq, we need select a VQ, then the question is:
1, which VQ to select? VQ0 or a random one? this leads confusing. 2, The virtio spec defines: Each device can have zero or more virtqueues
{ - size_t max_segment_size = SIZE_MAX; + u32 max_segment_size = U32_MAX; - if (vring_use_dma_api(vdev)) - max_segment_size = dma_max_mapping_size(vdev->dev.parent); + if (vring_use_dma_api(vdev)) { + size_t max_dma_size = dma_max_mapping_size(vdev->dev.parent); + + if (max_dma_size < max_segment_size) + max_segment_size = max_dma_size; + } return max_segment_size; } diff --git a/include/linux/virtio.h b/include/linux/virtio.h index b93238db94e3..1a605f408329 100644 --- a/include/linux/virtio.h +++ b/include/linux/virtio.h @@ -147,7 +147,7 @@ int virtio_device_restore(struct virtio_device *dev); #endif void virtio_reset_device(struct virtio_device *dev); -size_t virtio_max_dma_size(const struct virtio_device *vdev); +u32 virtio_max_dma_size(const struct virtio_device *vdev); #define virtio_device_for_each_vq(vdev, vq) \ list_for_each_entry(vq, &vdev->vqs, list) -- 2.20.1
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