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mx.microsoft.com 1; spf=pass smtp.mailfrom=intel.com; dmarc=pass action=none header.from=intel.com; dkim=pass header.d=intel.com; arc=none Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=intel.com; Received: from DS0PR11MB7529.namprd11.prod.outlook.com (2603:10b6:8:141::20) by LV8PR11MB8723.namprd11.prod.outlook.com (2603:10b6:408:1f8::14) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8835.28; Tue, 17 Jun 2025 06:42:52 +0000 Received: from DS0PR11MB7529.namprd11.prod.outlook.com ([fe80::d244:15cd:1060:941a]) by DS0PR11MB7529.namprd11.prod.outlook.com ([fe80::d244:15cd:1060:941a%7]) with mapi id 15.20.8835.027; Tue, 17 Jun 2025 06:42:52 +0000 Message-ID: Date: Tue, 17 Jun 2025 14:48:58 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH rfcv3 15/21] intel_iommu: Bind/unbind guest page table to host To: Nicolin Chen CC: "Duan, Zhenzhong" , Peter Xu , "qemu-devel@nongnu.org" , "alex.williamson@redhat.com" , "clg@redhat.com" , "eric.auger@redhat.com" , "mst@redhat.com" , "jasowang@redhat.com" , "ddutile@redhat.com" , "jgg@nvidia.com" , "shameerali.kolothum.thodi@huawei.com" , "joao.m.martins@oracle.com" , "clement.mathieu--drif@eviden.com" , "Tian, Kevin" , "Peng, Chao P" , Yi Sun , Marcel Apfelbaum , Paolo Bonzini , Richard Henderson , Eduardo Habkost References: <20250521111452.3316354-16-zhenzhong.duan@intel.com> <0f8087f4-0c97-440d-84d2-f3f017f81041@intel.com> <29f5f434-1fe3-4b5e-91d1-f153e1e98602@intel.com> <6f0cb11d-ab12-4ae1-98d0-eb44bb0a7f4f@intel.com> Content-Language: en-US From: Yi Liu In-Reply-To: Content-Type: text/plain; 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envelope-from=yi.l.liu@intel.com; helo=mgamail.intel.com X-Spam_score_int: -62 X-Spam_score: -6.3 X-Spam_bar: ------ X-Spam_report: (-6.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.892, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 2025/6/17 11:22, Nicolin Chen wrote: > On Mon, Jun 16, 2025 at 03:38:26PM +0800, Yi Liu wrote: >> On 2025/6/16 13:59, Nicolin Chen wrote: >>> On Thu, Jun 12, 2025 at 08:53:40PM +0800, Yi Liu wrote: >>>>>> That being said, IOMMU_NOTIFIER_IOTLB_EVENTS should not be needed >>>>>> for passthrough devices, right? >>>>> >>>>> No, even if x-flts=on is configured in QEMU cmdline, that only mean virtual vtd >>>>> supports stage-1 translation, guest still can choose to run in legacy mode(stage2), >>>>> e.g., with kernel cmdline intel_iommu=on,sm_off >>>>> >>>>> So before guest run, we don't know which kind of page table either stage1 or stage2 >>>>> for this VFIO device by guest. So we have to use iommu AS to catch stage2's MAP event >>>>> if guest choose stage2. >>>> >>>> @Zheznzhong, if guest decides to use legacy mode then vIOMMU should switch >>>> the MRs of the device's AS, hence the IOAS created by VFIO container would >>>> be switched to using the IOMMU_NOTIFIER_IOTLB_EVENTS since the MR is >>>> switched to IOMMU MR. So it should be able to support shadowing the guest >>>> IO page table. Hence, this should not be a problem. >>>> >>>> @Nicolin, I think your major point is making the VFIO container IOAS as a >>>> GPA IOAS (always return system AS in get_address_space op) and reusing it >>>> when setting nested translation. Is it? I think it should work if: >>>> 1) we can let the vfio memory listener filter out the RO pages per vIOMMU's >>>> request. >>> >>> Yes. >>> >>>> But I don't want the get_address_space op always return system >>>> AS as the reason mentioned by Zhenzhong above. >>> >>> So, you mean the VT-d model would need a runtime notification to >>> switch the address space of the VFIO ioas? >> >> It's not a notification. It's done by switching AS. Detail can be found >> in vtd_switch_address_space(). > > OK. I got confused about the "switch", thinking that was about > the get_address_space() call. yeah, not that call. The all magic is the MR enable/disable. This will switch to iommu MR hence the vfio_listener_region_add() will see the MR is iommu MR and register iommu notifier. >>> TBH, I am still unclear how many cases the VT-d model would need >>> support here :-/ >>> >>>> 2) we can disallow emulated/passthru devices behind the same pcie-pci >>>> bridge[1]. For emulated devices, AS should switch to iommu MR, while for >>>> passthru devices, it needs the AS stick with the system MR hence be able >>>> to keep the VFIO container IOAS as a GPA IOAS. To support this, let AS >>>> switch to iommu MR and have a separate GPA IOAS is needed. This separate >>>> GPA IOAS can be shared by all the passthru devices. >>> >>> Yea, ARM is doing in a similar way. >>> >>>> So basically, we are ok with your idea. But we should decide if it is >>>> necessary to support the topology in 2). I think this is a general >>>> question. TBH. I don't have much information to judge if it is valuable. >>>> Perhaps, let's hear from more people. >>> >>> I would be okay if VT-d decides to move on with its own listener, >>> if it turns out to be the relatively better case. But for ARM, I'd >>> like to see we can reuse the VFIO container IOAS. >> >> I didn't see a problem so far on this part. Have you seen any? > > Probably no functional problem with that internal listener. ARM > could work using one like that as well. The only problem is code > duplication. It's not ideal for everybody to have an internal S2 > listener while wasting the VFIO one. > > But given that VT-d has more complicated use cases like runtime > guest-level configuration that switches between nesting and non- > nesting modes, perhaps having an internal listener is a better > idea? I noticed there is quite a few duplication now (container/ioas/hwpt). let's see if anyone wants to put the emulated device and passthru devices under the same pci bridge. If no, let's avoid duplicating code. -- Regards, Yi Liu