[PATCH v2 04/12] virtio_ring: return -ENOMEM when a packed ring mapping fails

[Alexander Graf <graf@amazon.com>]

Commit f7728002c1c7 ("virtio_ring: fix return code on DMA mapping
fails") moved virtqueue_add_split() and virtqueue_add_indirect_packed()
to -ENOMEM, because virtio_queue_rq() maps -EIO to BLK_STS_IOERR and
the request fails. We still return -EIO from virtqueue_add_packed(),
and virtqueue_add_packed_in_order() copied that when it was added later.

Guests that bounce their I/O through swiotlb (SEV-SNP, TDX, s390 secure
execution) run the pool out with enough I/O in flight. On a split ring
virtio_queue_rq() reports BLK_STS_RESOURCE and the block layer requeues
the request. On a packed ring virtio_queue_rq() reports BLK_STS_IOERR
instead and the error reaches the filesystem.

Return -ENOMEM from the packed unmap_release paths too. Both are reached
from a single goto on a failed mapping, which is where
vring_map_one_sg() already produces -ENOMEM.

That way every ring layout reports the same errno, and the block layer
requeues the request instead of failing it.

Fixes: f7728002c1c7 ("virtio_ring: fix return code on DMA mapping fails")
Fixes: f6a15d854986 ("virtio_ring: add in order support")
Assisted-by: Kiro:claude-opus-5 checkpatch sparse
Signed-off-by: Alexander Graf <graf@amazon.com>
---
 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 ea8e774b6d8e..b7b03166a301 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1810,7 +1810,7 @@ static inline int virtqueue_add_packed(struct vring_virtqueue *vq,
 	}
 
 	END_USE(vq);
-	return -EIO;
+	return -ENOMEM;
 }
 
 static inline int virtqueue_add_packed_in_order(struct vring_virtqueue *vq,
@@ -1966,7 +1966,7 @@ static inline int virtqueue_add_packed_in_order(struct vring_virtqueue *vq,
 	}
 
 	END_USE(vq);
-	return -EIO;
+	return -ENOMEM;
 }
 
 static bool virtqueue_kick_prepare_packed(struct vring_virtqueue *vq)