netdev - Re: [PATCH V2 4/9] vhost: reset invalidate_count in vhost_set_vring_num

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Message-ID: <20190731193252.GH3946@ziepe.ca>
Date:   Wed, 31 Jul 2019 16:32:52 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH V2 4/9] vhost: reset invalidate_count in
 vhost_set_vring_num_addr()

On Wed, Jul 31, 2019 at 09:29:28PM +0800, Jason Wang wrote:
> 
> On 2019/7/31 下午8:41, Jason Gunthorpe wrote:
> > On Wed, Jul 31, 2019 at 04:46:50AM -0400, Jason Wang wrote:
> > > The vhost_set_vring_num_addr() could be called in the middle of
> > > invalidate_range_start() and invalidate_range_end(). If we don't reset
> > > invalidate_count after the un-registering of MMU notifier, the
> > > invalidate_cont will run out of sync (e.g never reach zero). This will
> > > in fact disable the fast accessor path. Fixing by reset the count to
> > > zero.
> > > 
> > > Reported-by: Michael S. Tsirkin <mst@...hat.com>
> > Did Michael report this as well?
> 
> 
> Correct me if I was wrong. I think it's point 4 described in
> https://lkml.org/lkml/2019/7/21/25.

I'm not sure what that is talking about

But this fixes what I described:

https://lkml.org/lkml/2019/7/22/554

Jason