diff options
author | Yuan Yao | 2023-08-08 05:10:59 +0000 |
---|---|---|
committer | Greg Kroah-Hartman | 2023-09-13 09:42:59 +0200 |
commit | ad8900dd8a568288cf6e332ffd4f11b2e74b17f4 (patch) | |
tree | 6dca279a35a90a0ab11a12c06f64ab4208f1588d /drivers/virtio | |
parent | 4927edc23edccc55284a8c929323e9fa6c5ce71f (diff) |
virtio_ring: fix avail_wrap_counter in virtqueue_add_packed
[ Upstream commit 1acfe2c1225899eab5ab724c91b7e1eb2881b9ab ]
In current packed virtqueue implementation, the avail_wrap_counter won't
flip, in the case when the driver supplies a descriptor chain with a
length equals to the queue size; total_sg == vq->packed.vring.num.
Let’s assume the following situation:
vq->packed.vring.num=4
vq->packed.next_avail_idx: 1
vq->packed.avail_wrap_counter: 0
Then the driver adds a descriptor chain containing 4 descriptors.
We expect the following result with avail_wrap_counter flipped:
vq->packed.next_avail_idx: 1
vq->packed.avail_wrap_counter: 1
But, the current implementation gives the following result:
vq->packed.next_avail_idx: 1
vq->packed.avail_wrap_counter: 0
To reproduce the bug, you can set a packed queue size as small as
possible, so that the driver is more likely to provide a descriptor
chain with a length equal to the packed queue size. For example, in
qemu run following commands:
sudo qemu-system-x86_64 \
-enable-kvm \
-nographic \
-kernel "path/to/kernel_image" \
-m 1G \
-drive file="path/to/rootfs",if=none,id=disk \
-device virtio-blk,drive=disk \
-drive file="path/to/disk_image",if=none,id=rwdisk \
-device virtio-blk,drive=rwdisk,packed=on,queue-size=4,\
indirect_desc=off \
-append "console=ttyS0 root=/dev/vda rw init=/bin/bash"
Inside the VM, create a directory and mount the rwdisk device on it. The
rwdisk will hang and mount operation will not complete.
This commit fixes the wrap counter error by flipping the
packed.avail_wrap_counter, when start of descriptor chain equals to the
end of descriptor chain (head == i).
Fixes: 1ce9e6055fa0 ("virtio_ring: introduce packed ring support")
Signed-off-by: Yuan Yao <yuanyaogoog@chromium.org>
Message-Id: <20230808051110.3492693-1-yuanyaogoog@chromium.org>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'drivers/virtio')
-rw-r--r-- | drivers/virtio/virtio_ring.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 90d514c14179..7d320f799ca1 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -1449,7 +1449,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq, } } - if (i < head) + if (i <= head) vq->packed.avail_wrap_counter ^= 1; /* We're using some buffers from the free list. */ |