FAILED: patch "[PATCH] virtio_ring: fix return code on DMA mapping fails" failed to apply to 4.9-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f7728002c1c7bfa787b276a31c3ef458739b8e7c Mon Sep 17 00:00:00 2001
From: Halil Pasic <pasic@linux.ibm.com>
Date: Thu, 14 Nov 2019 13:46:46 +0100
Subject: [PATCH] virtio_ring: fix return code on DMA mapping fails

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.

Cc: stable@vger.kernel.org
Fixes: 780bc7903a32 ("virtio_ring: Support DMA APIs")
Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Tested-by: Michael Mueller <mimu@linux.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

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,