On Thu, May 18, 2017 at 04:45:23PM +0200, Maxime Coquelin wrote: > Hi Michael, > > On 05/18/2017 09:35 AM, Maxime Coquelin wrote: > > > > > > 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. > s/VHOST_USER_SET_VRING_KICK/VHOST_USER_SET_VRING_ENABLE/
Note that when protocol features are off ring is started in enabled state, but iommu requires protocol features. > I just looked at implementing this change, but I'm not convinced this is > the right thing to do. > > On backend side, it means saving temporarily the vhost_vring_addr struct > into the vq struct, and moving all what is done currently in > SET_VRING_ADDR handler to SET_VRING_ENABLE one. Yes, and this is consistent with what the kernel does. > My understanding of the "Starting and stopping rings" chapter of the > spec is that the ring must not be processed as long as not started and > enabled, not that the addresses passed should not be checked/translated > as it is done today both in DPDK and libvhost-user. > > If the addresses are invalid, isn't it better to know as soon as > possible? > > Cheers, > Maxime There could be valid reasons to set an invalid address temporarily. For example to make sure connection is reset. -- MST