From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46190) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dBNIo-0000NT-Lt for qemu-devel@nongnu.org; Thu, 18 May 2017 11:25:23 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dBNIj-0006M2-OY for qemu-devel@nongnu.org; Thu, 18 May 2017 11:25:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51610) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dBNIj-0006Lc-Ej for qemu-devel@nongnu.org; Thu, 18 May 2017 11:25:17 -0400 Date: Thu, 18 May 2017 18:24:59 +0300 From: "Michael S. Tsirkin" Message-ID: <20170518181945-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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <34ccd41c-d799-21d9-ecf3-3903b68a24ea@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 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