Re: [dpdk-dev] [PATCH] vhost: fix vhost user virtqueue not accessable

["Liu, Yong" <yong.liu@intel.com>]

> -----Original Message-----
> From: Adrian Moreno [mailto:amorenoz@redhat.com]
> Sent: Friday, October 25, 2019 8:21 PM
> To: Liu, Yong <yong.liu@intel.com>; maxime.coquelin@redhat.com; Bie, Tiwei
> <tiwei.bie@intel.com>; Wang, Zhihong <zhihong.wang@intel.com>
> Cc: dev@dpdk.org
> Subject: Re: [PATCH] vhost: fix vhost user virtqueue not accessable
> 
> Hi Marvin,
> 
> On 10/25/19 6:20 PM, Marvin Liu wrote:
> > Log feature is disabled in vhost user, so that log address was invalid
> > when checking. Add feature bit check can skip useless address check.
> >
> Just so I understand, what conditions is the log address invalid?
> 
> > Fixes: 04cfc7fdbfca ("vhost: translate incoming log address to gpa")
> >
> > Signed-off-by: Marvin Liu <yong.liu@intel.com>
> > ---
> >  lib/librte_vhost/vhost_user.c | 16 +++++++++-------
> >  1 file changed, 9 insertions(+), 7 deletions(-)
> >
> > diff --git a/lib/librte_vhost/vhost_user.c
> b/lib/librte_vhost/vhost_user.c
> > index 61ef699ac..0407fdc29 100644
> > --- a/lib/librte_vhost/vhost_user.c
> > +++ b/lib/librte_vhost/vhost_user.c
> > @@ -741,13 +741,15 @@ translate_ring_addresses(struct virtio_net *dev,
> int vq_index)
> >  		vq->last_avail_idx = vq->used->idx;
> >  	}
> >
> > -	vq->log_guest_addr =
> > -		translate_log_addr(dev, vq, addr->log_guest_addr);
> > -	if (vq->log_guest_addr == 0) {
> > -		RTE_LOG(DEBUG, VHOST_CONFIG,
> > -			"(%d) failed to map log_guest_addr .\n",
> > -			dev->vid);
> > -		return dev;
> > +	if (dev->features & (1ULL << VHOST_F_LOG_ALL)) {
> > +		vq->log_guest_addr =
> > +			translate_log_addr(dev, vq, addr->log_guest_addr);
> 
> VHOST_F_LOG_ALL is only negotiated once the migration has started (at least
> from
> qemu's perspective).
> That means that we will postponing the translation  of the log address to
> the
> vhost_user_set_vring_addr() call that follows the VHOST_F_LOG_ALL enabling.
> In
> that call there are (at least) two things that could go wrong and lead to a
> migration failure:
> - If VHOST_USER_F_PROTOCOL_FEATURES is not enabled, the address won't be
> translated:
> 
> vhost_user:795
> 	if ((vq->enabled && (dev->features &
> 				(1ULL << VHOST_USER_F_PROTOCOL_FEATURES))) ||
> 			access_ok) {
> 		dev = translate_ring_addresses(dev, msg->payload.addr.index);
> 		if (!dev)
> 			return RTE_VHOST_MSG_RESULT_ERR;
> 
> 		*pdev = dev;
> 	}
> 
> - If the IOMMU is enabled and there's a miss, we would have to wait for the
> IOTLB_UPDATE and during that time, there would be failed accesses to the
> (still
> untranslated) log address.
> 
> 

Thanks, Adrian. 
Log address can be zero when logging is not enabled.
How about add other criteria after translation? Log address will be translated anyway and not affect vq status.

        vq->log_guest_addr =
                translate_log_addr(dev, vq, addr->log_guest_addr);
-       if (vq->log_guest_addr == 0) {
+       if (vq->log_guest_addr == 0 && addr->flags) {
                RTE_LOG(DEBUG, VHOST_CONFIG,
                        "(%d) failed to map log_guest_addr .\n",
                        dev->vid);
                return dev;
        }

Meanwhile, log address of packed ring is fixed to zero. Is any special reason to do that? 

Regards,
Marvin

> 
> > +		if (vq->log_guest_addr == 0) {
> > +			RTE_LOG(DEBUG, VHOST_CONFIG,
> > +				"(%d) failed to map log_guest_addr .\n",
> > +				dev->vid);
> > +			return dev;
> > +		}
> >  	}
> >  	vq->access_ok = 1;
> >
> >
> Thanks,
> Adrian