netdev - Re: [PATCH v2 3/3] vdpa/mlx5: defer clear_virtqueues to until DRIVER

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Date:   Thu, 18 Feb 2021 14:37:10 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Si-Wei Liu <si-wei.liu@...cle.com>, Eli Cohen <elic@...dia.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 3/3] vdpa/mlx5: defer clear_virtqueues to until
 DRIVER_OK


On 2021/2/18 上午5:55, Si-Wei Liu wrote:
>
>
> On 2/16/2021 7:21 AM, Eli Cohen wrote:
>> On Thu, Feb 11, 2021 at 09:33:14AM +0200, Eli Cohen wrote:
>>> On Wed, Feb 10, 2021 at 01:48:00PM -0800, Si-Wei Liu wrote:
>>>> While virtq is stopped,  get_vq_state() is supposed to
>>>> be  called to  get  sync'ed  with  the latest internal
>>>> avail_index from device. The saved avail_index is used
>>>> to restate  the virtq  once device is started.  Commit
>>>> b35ccebe3ef7 introduced the clear_virtqueues() routine
>>>> to  reset  the saved  avail_index,  however, the index
>>>> gets cleared a bit earlier before get_vq_state() tries
>>>> to read it. This would cause consistency problems when
>>>> virtq is restarted, e.g. through a series of link down
>>>> and link up events. We  could  defer  the  clearing of
>>>> avail_index  to  until  the  device  is to be started,
>>>> i.e. until  VIRTIO_CONFIG_S_DRIVER_OK  is set again in
>>>> set_status().
>>>>
>>>> Fixes: b35ccebe3ef7 ("vdpa/mlx5: Restore the hardware used index 
>>>> after change map")
>>>> Signed-off-by: Si-Wei Liu <si-wei.liu@...cle.com>
>>>> Acked-by: Jason Wang <jasowang@...hat.com>
>>> Acked-by: Eli Cohen <elic@...dia.com>
>>>
>> I take it back. I think we don't need to clear the indexes at all. In
>> case we need to restore indexes we'll get the right values through
>> set_vq_state(). If we suspend the virtqueue due to VM being suspended,
>> qemu will query first and will provide the the queried value. In case of
>> VM reboot, it will provide 0 in set_vq_state().
>>
>> I am sending a patch that addresses both reboot and suspend.
> With set_vq_state() repurposed to restoring used_index I'm fine with 
> this approach.
>
> Do I have to repost a v3 of this series while dropping the 3rd patch?
>
> -Siwei 


Yes, please.

Thanks