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Wed, 6 Nov 2024 08:41:11 +0000 Message-ID: Date: Wed, 6 Nov 2024 16:45:47 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 02/13] iommu/vt-d: Add a helper to flush cache for updating present pasid entry To: "Tian, Kevin" , "joro@8bytes.org" , "jgg@nvidia.com" , "baolu.lu@linux.intel.com" CC: "alex.williamson@redhat.com" , "eric.auger@redhat.com" , "nicolinc@nvidia.com" , "kvm@vger.kernel.org" , "chao.p.peng@linux.intel.com" , "iommu@lists.linux.dev" , "Duan, Zhenzhong" , "vasant.hegde@amd.com" , "will@kernel.org" References: <20241104131842.13303-1-yi.l.liu@intel.com> <20241104131842.13303-3-yi.l.liu@intel.com> Content-Language: en-US From: Yi Liu In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SG2PR06CA0188.apcprd06.prod.outlook.com (2603:1096:4:1::20) To DS0PR11MB7529.namprd11.prod.outlook.com (2603:10b6:8:141::20) Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7529:EE_|SJ0PR11MB5792:EE_ X-MS-Office365-Filtering-Correlation-Id: 616d615e-c7a7-4508-ab5d-08dcfe3ec45e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016|7416014; 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Hence, add a helper for it. Per the >> VT-d spec, the changes to the fields other than SSADE and P bit can >> share the same code. So intel_pasid_setup_page_snoop_control() is the >> first user of this helper. > > No hw spec would ever talk about coding sharing in sw implementation. yes, it's just sw choice. > and according to the following context the fact is just that two flows > between RID and PASID are similar so you decide to create a common > helper for both. I'm not quite getting why RID is related. This is only about the cache flush per pasid entry updating. >> >> No functional change is intended. >> >> Signed-off-by: Yi Liu >> --- >> drivers/iommu/intel/pasid.c | 54 ++++++++++++++++++++++++------------- >> 1 file changed, 36 insertions(+), 18 deletions(-) >> >> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c >> index 977c4ac00c4c..81d038222414 100644 >> --- a/drivers/iommu/intel/pasid.c >> +++ b/drivers/iommu/intel/pasid.c >> @@ -286,6 +286,41 @@ static void pasid_flush_caches(struct intel_iommu >> *iommu, >> } >> } >> >> +/* >> + * This function is supposed to be used after caller updates the fields >> + * except for the SSADE and P bit of a pasid table entry. It does the >> + * below: >> + * - Flush cacheline if needed >> + * - Flush the caches per the guidance of VT-d spec 5.0 Table 28. > > while at it please add the name for the table. sure. > >> + * ”Guidance to Software for Invalidations“ >> + * >> + * Caller of it should not modify the in-use pasid table entries. > > I'm not sure about this statement. As long as the change doesn't > impact in-fly DMAs it's always the caller's right for whether to do it. > > actually based on the main intention of supporting replace it's > quite possible. This comment is mainly due to the clflush_cache_range() within this helper. If caller modifies the pte content, it will need to call this again. > otherwise this looks good, > > Reviewed-by: Kevin Tian -- Regards, Yi Liu