Re: [PATCH] vhost: fix initialization for vq->is_le

[Halil Pasic <pasic@linux.vnet.ibm.com>]

On 01/31/2017 07:28 PM, Michael S. Tsirkin wrote:
> On Tue, Jan 31, 2017 at 04:56:13PM +0100, Halil Pasic wrote:
>>
>>
>> On 01/30/2017 08:06 PM, Greg Kurz wrote:
>>>> Currently, under certain circumstances vhost_init_is_le does just a part
>>>> of the initialization job, and depends on vhost_reset_is_le being called
>>>> too. For this reason vhost_vq_init_access used to call vhost_reset_is_le
>>>> when vq->private_data is NULL. This is not only counter intuitive, but
>>>> also real a problem because it breaks vhost_net. The bug was introduced to
>>>> vhost_net with commit 2751c9882b94 ("vhost: cross-endian support for
>>>> legacy devices"). The symptom is corruption of the vq's used.idx field
>>>> (virtio) after VHOST_NET_SET_BACKEND was issued as a part of the vhost
>>>> shutdown on a vq with pending descriptors.
>>>>
>>>> Let us make sure the outcome of vhost_init_is_le never depend on the state
>>>> it is actually supposed to initialize, and fix virtio_net by removing the
>>>> reset from vhost_vq_init_access.
>>>>
>>>> With the above, there is no reason for vhost_reset_is_le to do just half
>>>> of the job. Let us make vhost_reset_is_le reinitialize is_le.
>>>>
>>>> Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
>>>> Reported-by: Michael A. Tebolt <miket@us.ibm.com>
>>>> Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>>>> Fixes: commit 2751c9882b94 ("vhost: cross-endian support for legacy devices")
>>>> ---
>>> Reviewed-by: Greg Kurz <groug@kaod.org>
>>>
>>
>> Thanks! 
>>
>> We have some tests on s390x (that is BE) running, but I won't be able to
>> test the change with cross endian and legacy. 
>>
>> What do you think, should I/we RFT or are we fine without?
>>
>> Regards,
>> Halil
> 
> More testing can't hurt. I can merge this meanwhile.
> 

I received a word from our test team. No problems discovered with
 a mix of legacy and virtio 1 guests on s390x (was reliably
reproducible without this patch with the same setup).
Could you please add:

Tested-by: Michael A. Tebolt <miket@us.ibm.com>

Regards,
Halil