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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id u4sm29623865qkb.16.2019.07.31.05.41.24 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 31 Jul 2019 05:41:24 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hsnv2-0006PN-6Q; Wed, 31 Jul 2019 09:41:24 -0300 Date: Wed, 31 Jul 2019 09:41:24 -0300 From: Jason Gunthorpe To: Jason Wang Cc: mst@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH V2 4/9] vhost: reset invalidate_count in vhost_set_vring_num_addr() Message-ID: <20190731124124.GD3946@ziepe.ca> References: <20190731084655.7024-1-jasowang@redhat.com> <20190731084655.7024-5-jasowang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190731084655.7024-5-jasowang@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Did Michael report this as well? > Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address") > Signed-off-by: Jason Wang > drivers/vhost/vhost.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 2a3154976277..2a7217c33668 100644 > +++ b/drivers/vhost/vhost.c > @@ -2073,6 +2073,10 @@ static long vhost_vring_set_num_addr(struct vhost_dev *d, > d->has_notifier = false; > } > > + /* reset invalidate_count in case we are in the middle of > + * invalidate_start() and invalidate_end(). > + */ > + vq->invalidate_count = 0; > vhost_uninit_vq_maps(vq); > #endif >