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([2a01:e0a:59e:9d80:527b:9dff:feef:3874]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38dbdd5c87csm2212774f8f.52.2025.02.06.08.44.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Feb 2025 08:44:08 -0800 (PST) Message-ID: <455143f1-db4f-40d0-a2e2-fc983476f76e@redhat.com> Date: Thu, 6 Feb 2025 17:44:04 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable nested SMMUv3 Content-Language: en-US To: =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= Cc: Shameerali Kolothum Thodi , Jason Gunthorpe , "qemu-arm@nongnu.org" , "qemu-devel@nongnu.org" , "peter.maydell@linaro.org" , "nicolinc@nvidia.com" , "ddutile@redhat.com" , Linuxarm , "Wangzhou (B)" , jiangkunkun , Jonathan Cameron , "zhangfei.gao@linaro.org" , Nathan Chen References: <20241108125242.60136-1-shameerali.kolothum.thodi@huawei.com> <7ecabe74e0514367baf28d67675e5db8@huawei.com> <20250131142404.GP5556@nvidia.com> <3efcea1171af4b2f81be842f2c55fe51@huawei.com> <20250131145411.GR5556@nvidia.com> <20039bbc40df453a8a41a863d74b9ff9@huawei.com> From: Eric Auger In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=eric.auger@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, 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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: eric.auger@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 2/6/25 9:53 AM, Daniel P. Berrangé wrote: > On Fri, Jan 31, 2025 at 05:08:28PM +0100, Eric Auger wrote: >> Hi, >> >> >> On 1/31/25 4:23 PM, Shameerali Kolothum Thodi wrote: >>>> -----Original Message----- >>>> From: Jason Gunthorpe >>>> Sent: Friday, January 31, 2025 2:54 PM >>>> To: Shameerali Kolothum Thodi >>>> Cc: Daniel P. Berrangé ; qemu-arm@nongnu.org; >>>> qemu-devel@nongnu.org; eric.auger@redhat.com; >>>> peter.maydell@linaro.org; nicolinc@nvidia.com; ddutile@redhat.com; >>>> Linuxarm ; Wangzhou (B) >>>> ; jiangkunkun ; >>>> Jonathan Cameron ; >>>> zhangfei.gao@linaro.org; Nathan Chen >>>> Subject: Re: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable >>>> nested SMMUv3 >>>> >>>> On Fri, Jan 31, 2025 at 02:39:53PM +0000, Shameerali Kolothum Thodi >>>> wrote: >>>> >>>>>>> And Qemu does some checking to make sure that the device is indeed >>>>>> associated >>>>>>> with the specified phys-smmuv3. This can be done going through the >>>>>> sysfs path checking >>>>>>> which is what I guess libvirt is currently doing to populate the >>>> topology. >>>>>> So basically >>>>>>> Qemu is just replicating that to validate again. >>>>>> I would prefer that iommufd users not have to go out to sysfs.. >>>>>> >>>>>>> Or another option is extending the IOMMU_GET_HW_INFO IOCTL to >>>>>> return the phys >>>>>>> smmuv3 base address which can avoid going through the sysfs. >>>>>> It also doesn't seem great to expose a physical address. But we could >>>>>> have an 'iommu instance id' that was a unique small integer? >>>>> Ok. But how the user space can map that to the device? >>>> Why does it need to? >>>> >>>> libvirt picks some label for the vsmmu instance, it doesn't matter >>>> what the string is. >>>> >>>> qemu validates that all of the vsmmu instances are only linked to PCI >>>> device that have the same iommu ID. This is already happening in the >>>> kernel, it will fail attaches to mismatched instances. >>>> >>>> Nothing further is needed? >>> -device pxb-pcie,id=pcie.1,bus_nr=8,bus=pcie.0 \ >>> -device pcie-root-port,id=pcie.port1,bus=pcie.1,chassis=1 \ >>> -device arm-smmuv3-accel,bus=pcie.1,id=smmuv1 \ >> I don't get what is the point of adding such an id if it is not >> referenced anywhere? > Every QDev device instance has an 'id' property - if you don't > set one explicitly, QEMU will generate one internally. Libvirt > will always set the 'id' property to avoid the internal auto- > generated IDs, as it wants full knowledge of naming. OK thank you for the explanation Eric > > With regards, > Daniel