Re: [Qemu-devel] [PATCH 3/6] vhost: Update rings information for IOTLB earlier

[Maxime Coquelin]

On 05/17/2017 06:41 PM, Michael S. Tsirkin wrote:
> On Fri, May 12, 2017 at 01:21:18PM +0200, Maxime Coquelin wrote:
> > On 05/11/2017 07:33 PM, Michael S. Tsirkin wrote:
> > > On Thu, May 11, 2017 at 02:32:43PM +0200, Maxime Coquelin wrote:
> > > > Vhost-kernel backend need to receive IOTLB entries for rings
> > > > information early, but vhost-user need the same information
> > > > earlier, before VHOST_USER_SET_VRING_ADDR is sent.
> > > Weird. What does VHOST_USER_SET_VRING_ADDR have to do with it?
> > >
> > > According to
> > >         Starting and stopping rings
> > > in vhost user spec, vhost user does not access
> > > anything until ring is started and enabled.
> > >
> > >
> > > > This patch also trigger IOTLB miss for all rings informations
> > > > for robustness, even if in practice these adresses are on the
> > > > same page.
> > Actually, the DPDK vhost-user backend is compliant with the spec,
> > but when handling VHOST_USER_SET_VRING_ADDR request, it translates the
> > guest addresses into backend VAs, and check they are valid. I will make the
> > commit message clearer about this in next revision.
> >
> > The check could be done later, for example when the ring are started,
> > but it wouldn't change the need to trigger a miss at some point.
> I think it should be done later, yes. As long as ring is not
> started addresses should not be interpreted.

Ok, then I'll move these addresses translations in the
VHOST_USER_SET_VRING_KICK handler.

Thanks,
Maxime