On Fri, May 19, 2017 at 11:48:52AM +0200, Maxime Coquelin wrote: > > > On 05/18/2017 05:24 PM, Michael S. Tsirkin wrote: > > 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. > > OK, I will take care of this. > > Note that currently in DPDK, the ring is created in enabled state, > so it is enabled as soon as started even with protocol features. > I have done the patch to fix this, will be posted with the patch that > do the ring addresses translations only when starting/enabling the ring. > > Also, note that disabling VHOST_USER_F_PROTOCOL_FEATURES with latest > DPDK and QEMU seems broken. I'll add this to my todo list to understand > where the problem is, but this is lower priority.
And hopefully add a unit test without this so we don't break it in the future. > > > 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. > > Ok. > > Thanks, > Maxime