Re: [Qemu-devel] [PATCH] qtest: virtio: zeroed last VRingDesc after allocate

[Stefan Hajnoczi]

On Sat, Jan 14, 2017 at 05:59:36PM +0800, Longpeng(Mike) wrote:
> As qvring_indirect_desc_setup() wouldn't initialize last VRingDesc,
> so it's filled with dirty data, this might cause virtio backend broken.
> 
> For example, the last bit of this VRingDesc's flags might be 1, so
> virtqueue_read_next_desc() would report "Desc next is ***".
> 
> This patch zeored the last VRingDesc in qvring_indirect_desc_setup().
> 
> Signed-off-by: Longpeng(Mike) <address@hidden>
> ---
>  tests/libqos/virtio.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/tests/libqos/virtio.c b/tests/libqos/virtio.c
> index ec30cb9..b29c69e 100644
> --- a/tests/libqos/virtio.c
> +++ b/tests/libqos/virtio.c
> @@ -171,12 +171,20 @@ QVRingIndirectDesc 
> *qvring_indirect_desc_setup(QVirtioDevice *d,
>      for (i = 0; i < elem - 1; ++i) {
>          /* indirect->desc[i].addr */
>          writeq(indirect->desc + (16 * i), 0);
> +        /* indirect->desc[i].len */
> +        writeq(indirect->desc + (16 * i) + 8, 0);

The len field is 32 bits long.  Please use writel().

>          /* indirect->desc[i].flags */
>          writew(indirect->desc + (16 * i) + 12, VRING_DESC_F_NEXT);
>          /* indirect->desc[i].next */
>          writew(indirect->desc + (16 * i) + 14, i + 1);
>      }
>  
> +    /* zeroed last element */
> +    writeq(indirect->desc + (16 * i), 0); /* addr */
> +    writeq(indirect->desc + (16 * i) + 8, 0); /*len*/

Same here.

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