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Wed, 8 Jul 2020 05:42:32 +0000 (UTC) Subject: Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier To: Peter Xu References: <54d2cdfd-97b8-9e1d-a607-d7a5e96be3a1@redhat.com> <20200629133403.GA266532@xz-x1> <2589d0e9-cc5b-a4df-8790-189b49f1a40e@redhat.com> <20200630153911.GD3138@xz-x1> <69f6d6e7-a0b1-abae-894e-4e81b7e0cc90@redhat.com> <20200702154540.GI40675@xz-x1> <34fe0e55-c0ae-8e56-462b-6281b6cca4f5@redhat.com> <20200703130338.GD6677@xz-x1> <20200707195429.GF88106@xz-x1> From: Jason Wang Message-ID: <5004a059-6eb0-4ef3-40b7-94dfbf9ec08f@redhat.com> Date: Wed, 8 Jul 2020 13:42:30 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200707195429.GF88106@xz-x1> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jasowang@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/07 17:25:10 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Yan Zhao , "Michael S. Tsirkin" , "libvir-list@redhat.com" , Juan Quintela , qemu-devel@nongnu.org, =?UTF-8?Q?Eugenio_P=c3=a9rez?= , Eric Auger , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/7/8 上午3:54, Peter Xu wrote: > On Tue, Jul 07, 2020 at 04:03:10PM +0800, Jason Wang wrote: >> On 2020/7/3 下午9:03, Peter Xu wrote: >>> On Fri, Jul 03, 2020 at 03:24:19PM +0800, Jason Wang wrote: >>>> On 2020/7/2 下午11:45, Peter Xu wrote: >>>>> On Thu, Jul 02, 2020 at 11:01:54AM +0800, Jason Wang wrote: >>>>>> So I think we agree that a new notifier is needed? >>>>> Good to me, or a new flag should be easier (IOMMU_NOTIFIER_DEV_IOTLB)? >>>> That should work but I wonder something as following is better. >>>> >>>> Instead of introducing new flags, how about carry the type of event in the >>>> notifier then the device (vhost) can choose the message it want to process >>>> like: >>>> >>>> static vhost_iommu_event(IOMMUNotifier *n, IOMMUTLBEvent *event) >>>> >>>> { >>>> >>>> switch (event->type) { >>>> >>>> case IOMMU_MAP: >>>> case IOMMU_UNMAP: >>>> case IOMMU_DEV_IOTLB_UNMAP: >>>> ... >>>> >>>> } >>> Looks ok to me, though imo we should still keep the registration information, >>> so VT-d knows which notifiers is interested in which events. E.g., we can >>> still do something like vtd_as_has_map_notifier(). >> >> Is this for a better performance? >> >> I wonder whether it's worth since we can't not have both vhost and vtd to be >> registered into the same as. > /me failed to follow this sentence.. :( Sorry, I meant "vfio" instead "vtd". > >> So it should be functional equivalent to vtd_as_has_notifier(). > For example: in vtd_iommu_replay() we'll skip the replay if vhost has > registered the iommu notifier because vtd_as_has_map_notifier() will return > false. Two questions: - Do we care the performance here? If not, vhost may just ignore the MAP event? - If we care the performance, it's better to implement the MAP event for vhost, otherwise it could be a lot of IOTLB miss Thanks > It'll only return true if the device is a vfio-pci device. > > Without vtd_as_has_map_notifier(), how could we do that? >