From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52502) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dBeWx-00006c-1M for qemu-devel@nongnu.org; Fri, 19 May 2017 05:49:08 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dBeWu-0002pk-LH for qemu-devel@nongnu.org; Fri, 19 May 2017 05:49:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54878) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dBeWu-0002oe-Av for qemu-devel@nongnu.org; Fri, 19 May 2017 05:49:04 -0400 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> From: Maxime Coquelin Message-ID: <9f994094-348e-3be9-de6b-e5a22c1c10be@redhat.com> Date: Fri, 19 May 2017 11:48:52 +0200 MIME-Version: 1.0 In-Reply-To: <20170518181945-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit 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: "Michael S. Tsirkin" 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 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. >> 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