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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 SJ0PR11MB4798.namprd11.prod.outlook.com (2603:10b6:a03:2d5::12) by IA0PR11MB8398.namprd11.prod.outlook.com (2603:10b6:208:487::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9412.9; Thu, 11 Dec 2025 10:57:40 +0000 Received: from SJ0PR11MB4798.namprd11.prod.outlook.com ([fe80::d946:6abf:6e7e:fd1e]) by SJ0PR11MB4798.namprd11.prod.outlook.com ([fe80::d946:6abf:6e7e:fd1e%7]) with mapi id 15.20.9412.005; Thu, 11 Dec 2025 10:57:39 +0000 Message-ID: <4618ef6c-9f54-45bf-a95c-5f813f9a2365@intel.com> Date: Thu, 11 Dec 2025 19:04:24 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 02/23] intel_iommu: Delete RPS capability related supporting code To: Jason Wang , Zhenzhong Duan CC: , , , , , , , , , , , , , References: <20251117093729.1121324-1-zhenzhong.duan@intel.com> <20251117093729.1121324-3-zhenzhong.duan@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: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 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_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 2025/12/11 16:22, Jason Wang wrote: > On Mon, Nov 17, 2025 at 5:38 PM Zhenzhong Duan wrote: >> >> RID-PASID Support(RPS) is not set in vIOMMU ECAP register, the supporting >> code is there but never takes effect. >> >> Meanwhile, according to VTD spec section 3.4.3: >> "Implementations not supporting RID_PASID capability (ECAP_REG.RPS is 0b), >> use a PASID value of 0 to perform address translation for requests without >> PASID." >> >> We should delete the supporting code which fetches RID_PASID field from >> scalable context entry and use 0 as RID_PASID directly, because RID_PASID >> field is ignored if no RPS support according to spec. >> >> This simplifies the code and doesn't bring any penalty. >> >> Suggested-by: Yi Liu >> Signed-off-by: Zhenzhong Duan >> --- > > Is the feature deprecated in the spec? If not, it should be still > better to enable it. Hi Jason, The feature is still in the spec. However, using PASID#0 for the requests without pasid is aligned across vendors. So the linux iommu subsystem uses PASID#0 to differentiate the pasid path and non-pasid path like below: commit bc06f7f66de404ae6323963361fe4e2f5f71a1e5 Author: Yi Liu Date: Fri Mar 21 10:19:26 2025 -0700 iommufd/device: Only add reserved_iova in non-pasid path As the pasid is passed through the attach/replace/detach helpers, it is necessary to ensure only the non-pasid path adds reserved_iova. Link: https://patch.msgid.link/r/20250321171940.7213-5-yi.l.liu@intel.com Reviewed-by: Jason Gunthorpe Reviewed-by: Kevin Tian Reviewed-by: Nicolin Chen Reviewed-by: Lu Baolu Signed-off-by: Yi Liu Tested-by: Nicolin Chen Signed-off-by: Jason Gunthorpe diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c index 7051feda2fab..4625f084f7d0 100644 --- a/drivers/iommu/iommufd/device.c +++ b/drivers/iommu/iommufd/device.c @@ -483,6 +483,7 @@ int iommufd_hw_pagetable_attach(struct iommufd_hw_pagetable *hwpt, struct iommufd_device *idev, ioasid_t pasid) { struct iommufd_hwpt_paging *hwpt_paging = find_hwpt_paging(hwpt); + bool attach_resv = hwpt_paging && pasid == IOMMU_NO_PASID; int rc; So even though intel hardware report RPS=1, the linux intel iommu driver uses PASID#0 as rid_pasid and ignores the RPS value. So I don't think we will ever report RPS=1 to VM. Also, as Zhenzhong's commit message states, current vIOMMU does not report RPS, the logic to retrieve rid_pasid from context entry is not necessary as well. Based on the fact, I think it is nice to drop the support. Please let us know if you have other ideas. Regards, Yi Liu