netdev - Re: Re: Re: [PATCH v6 03/10] vhost-vdpa: protect concurrent access to vhost device iotlb

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Date:   Mon, 12 Apr 2021 05:00:33 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Yongji Xie <xieyongji@...edance.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christian Brauner <christian.brauner@...onical.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, viro@...iv.linux.org.uk,
        Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org,
        Jonathan Corbet <corbet@....net>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Re: Re: [PATCH v6 03/10] vhost-vdpa: protect concurrent access
 to vhost device iotlb

On Mon, Apr 12, 2021 at 10:29:17AM +0800, Yongji Xie wrote:
> On Mon, Apr 12, 2021 at 4:49 AM Michael S. Tsirkin <mst@...hat.com> wrote:
> >
> > On Sun, Apr 11, 2021 at 01:36:18PM +0800, Yongji Xie wrote:
> > > On Sat, Apr 10, 2021 at 12:16 AM Michael S. Tsirkin <mst@...hat.com> wrote:
> > > >
> > > > On Wed, Mar 31, 2021 at 04:05:12PM +0800, Xie Yongji wrote:
> > > > > Use vhost_dev->mutex to protect vhost device iotlb from
> > > > > concurrent access.
> > > > >
> > > > > Fixes: 4c8cf318("vhost: introduce vDPA-based backend")
> > > > > Cc: stable@...r.kernel.org
> > > > > Signed-off-by: Xie Yongji <xieyongji@...edance.com>
> > > > > Acked-by: Jason Wang <jasowang@...hat.com>
> > > > > Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>
> > > >
> > > > I could not figure out whether there's a bug there now.
> > > > If yes when is the concurrent access triggered?
> > > >
> > >
> > > When userspace sends the VHOST_IOTLB_MSG_V2 message concurrently?
> > >
> > > vhost_vdpa_chr_write_iter -> vhost_chr_write_iter ->
> > > vhost_vdpa_process_iotlb_msg()
> > >
> > > Thanks,
> > > Yongji
> >
> > And then what happens currently?
> >
> 
> Then we might access vhost_vdpa_map() concurrently and cause
> corruption of the list and interval tree in struct vhost_iotlb.
> 
> Thanks,
> Yongji

OK. Sounds like it's actually needed in this release if possible.  Pls
add this info in the commit log and post it as a separate patch. 

-- 
MST