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On Thu, 14 Nov 2019 13:46:46 +0100
Halil Pasic <pasic@xxxxxxxxxxxxx> wrote:
> Commit 780bc7903a32 ("virtio_ring: Support DMA APIs") makes
> virtqueue_add() return -EIO when we fail to map our I/O buffers. This is
> a very realistic scenario for guests with encrypted memory, as swiotlb
> may run out of space, depending on it's size and the I/O load.
>
> The virtio-blk driver interprets -EIO form virtqueue_add() as an IO
> error, despite the fact that swiotlb full is in absence of bugs a
> recoverable condition.
>
> Let us change the return code to -ENOMEM, and make the block layer
> recover form these failures when virtio-blk encounters the condition
> described above.
>
> Fixes: 780bc7903a32 ("virtio_ring: Support DMA APIs")
> Signed-off-by: Halil Pasic <pasic@xxxxxxxxxxxxx>
> Tested-by: Michael Mueller <mimu@xxxxxxxxxxxxx>
> ---
>
> Notes
> =====
>
> * When out of descriptors (which might regarded as a similar out of
> resources condition) virtio uses -ENOSPC, this however seems wrong,
> as ENOSPC is defined as -ENOSPC. Thus I choose -ENOMEM over -ENOSPC.
>
> * In virtio_queue_rq() in virtio_blk.c both -ENOMEM and -ENOSPC are
> handled as BLK_STS_DEV_RESOURCE. Returning BLK_STS_RESOURCE however
> seems more appropriate for dma mapping failed as we are talking about
> a global, and not a device local resource. Both seem to do the trick.
>
> * Mimu tested the patch with virtio-blk and virtio-net (thanks!). We
> should look into how other virtio devices behave when DMA mapping fails.
> ---
> drivers/virtio/virtio_ring.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index a8041e451e9e..867c7ebd3f10 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -583,7 +583,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
> kfree(desc);
>
> END_USE(vq);
> - return -EIO;
> + return -ENOMEM;
> }
>
> static bool virtqueue_kick_prepare_split(struct virtqueue *_vq)
> @@ -1085,7 +1085,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
> kfree(desc);
>
> END_USE(vq);
> - return -EIO;
> + return -ENOMEM;
> }
>
> static inline int virtqueue_add_packed(struct virtqueue *_vq,
