From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43609) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dBoeN-0006Ho-7H for qemu-devel@nongnu.org; Fri, 19 May 2017 16:37:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dBoeI-0000Gq-Az for qemu-devel@nongnu.org; Fri, 19 May 2017 16:37:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59976) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dBoeI-0000Gg-1Y for qemu-devel@nongnu.org; Fri, 19 May 2017 16:37:22 -0400 Date: Fri, 19 May 2017 23:37:13 +0300 From: "Michael S. Tsirkin" Message-ID: <20170519233654-mutt-send-email-mst@kernel.org> References: <20170511123246.31308-1-maxime.coquelin@redhat.com> <20170511123246.31308-4-maxime.coquelin@redhat.com> <20170511202154-mutt-send-email-mst@kernel.org> <8101cc11-51b7-9361-6506-25986aa652c4@redhat.com> <20170517194008-mutt-send-email-mst@kernel.org> <74684170-6dc8-3146-6a93-9c5dd723d1eb@redhat.com> <34ccd41c-d799-21d9-ecf3-3903b68a24ea@redhat.com> <20170518181945-mutt-send-email-mst@kernel.org> <9f994094-348e-3be9-de6b-e5a22c1c10be@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9f994094-348e-3be9-de6b-e5a22c1c10be@redhat.com> Subject: Re: [Qemu-devel] [PATCH 3/6] vhost: Update rings information for IOTLB earlier List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Maxime Coquelin Cc: peterx@redhat.com, marcandre.lureau@gmail.com, vkaplans@redhat.com, jasowang@redhat.com, wexu@redhat.com, yuanhan.liu@linux.intel.com, qemu-devel@nongnu.org, jfreiman@redhat.com 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