linux-kernel - Re: [PATCH v3 3/3] vhost: Improve vhost_get_avail_idx() with smp

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Date: Mon, 8 Apr 2024 14:15:24 +1000
From: Gavin Shan <gshan@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org,
 jasowang@...hat.com, will@...nel.org, davem@...emloft.net,
 stefanha@...hat.com, sgarzare@...hat.com, keirf@...gle.com,
 yihyu@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH v3 3/3] vhost: Improve vhost_get_avail_idx() with
 smp_rmb()

Hi Michael,

On 3/30/24 19:02, Gavin Shan wrote:
> On 3/28/24 19:31, Michael S. Tsirkin wrote:
>> On Thu, Mar 28, 2024 at 10:21:49AM +1000, Gavin Shan wrote:
>>> All the callers of vhost_get_avail_idx() are concerned to the memory
>>> barrier, imposed by smp_rmb() to ensure the order of the available
>>> ring entry read and avail_idx read.
>>>
>>> Improve vhost_get_avail_idx() so that smp_rmb() is executed when
>>> the avail_idx is advanced. With it, the callers needn't to worry
>>> about the memory barrier.
>>>
>>> Suggested-by: Michael S. Tsirkin <mst@...hat.com>
>>> Signed-off-by: Gavin Shan <gshan@...hat.com>
>>
>> Previous patches are ok. This one I feel needs more work -
>> first more code such as sanity checking should go into
>> this function, second there's actually a difference
>> between comparing to last_avail_idx and just comparing
>> to the previous value of avail_idx.
>> I will pick patches 1-2 and post a cleanup on top so you can
>> take a look, ok?
>>
> 
> Thanks, Michael. It's fine to me.
> 

A kindly ping.

If it's ok to you, could you please merge PATCH[1-2]? Our downstream
9.4 need the fixes, especially for NVidia's grace-hopper and grace-grace
platforms.

For PATCH[3], I also can help with the improvement if you don't have time
for it. Please let me know.

Thanks,
Gavin