Re: [PATCH 3/3] virtio-blk: Consider dma_max_mapping_size() for maximum segment size

Michael S. Tsirkin
2019-01-16T14:05:49Z

On Tue, Jan 15, 2019 at 02:22:57PM +0100, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
>
> Segments can't be larger than the maximum DMA mapping size
> supported on the platform. Take that into account when
> setting the maximum segment size for a block device.
>
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
> drivers/block/virtio_blk.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index b16a887bbd02..6193962a7fec 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -723,7 +723,7 @@ static int virtblk_probe(struct virtio_device *vdev)
> struct request_queue *q;
> int err, index;
>
> - u32 v, blk_size, sg_elems, opt_io_size;
> + u32 v, blk_size, max_size, sg_elems, opt_io_size;
> u16 min_io_size;
> u8 physical_block_exp, alignment_offset;
>
> @@ -826,14 +826,16 @@ static int virtblk_probe(struct virtio_device *vdev)
> /* No real sector limit. */
> blk_queue_max_hw_sectors(q, -1U);
>
> + max_size = dma_max_mapping_size(&vdev->dev);
> +

Should this be limited to ACCESS_PLATFORM?

I see no reason to limit this without as guest can
access any memory.

I'd like a bit of time to consider this point.

> /* Host can optionally specify maximum segment size and number of
> * segments. */
> err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
> struct virtio_blk_config, size_max, &v);
> if (!err)
> - blk_queue_max_segment_size(q, v);
> - else
> - blk_queue_max_segment_size(q, -1U);
> + max_size = min(max_size, v);
> +
> + blk_queue_max_segment_size(q, max_size);
>
> /* Host can optionally specify the block size of the device */
> err = virtio_cread_feature(vdev, VIRTIO_BLK_F_BLK_SIZE,
> --
> 2.17.1