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Mon, 24 Jun 2024 08:02:31 +0000 Message-ID: <15590835-ed6a-44a5-94b5-663f159653cc@intel.com> Date: Mon, 24 Jun 2024 16:06:26 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] iommu/vt-d: Remove hardware automatic ATS dependency To: Lu Baolu , Joerg Roedel , "Kevin Tian" , Jacob Pan CC: Will Deacon , Robin Murphy , , References: <20240624052501.253405-1-baolu.lu@linux.intel.com> <20240624052501.253405-2-baolu.lu@linux.intel.com> Content-Language: en-US From: Yi Liu In-Reply-To: <20240624052501.253405-2-baolu.lu@linux.intel.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SGXP274CA0006.SGPP274.PROD.OUTLOOK.COM (2603:1096:4:b8::18) 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_|MW5PR11MB5930:EE_ X-MS-Office365-Filtering-Correlation-Id: 7e839446-052c-46d8-9ac3-08dc9423ff4f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230037|376011|1800799021|366013; 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However, when IOMMU is > running in the legacy mode, ATS could be automatically supported by the > hardware so that the OS has no need to support the ATS functionality. It seems like if VT-d hw is operating in legacy mode, ATS is enabled automatically? This is really suprising. Maybe I got it wrongly. Could you elaborate a bit? > This is a backward compatibility feature which enables older OSs. Since > Linux VT-d implementation has already supported ATS features for a long > time, there is no need to rely on this compatibility hardware. Remove it > to make the driver future-proof. > > Signed-off-by: Lu Baolu > --- > drivers/iommu/intel/iommu.c | 9 +-------- > 1 file changed, 1 insertion(+), 8 deletions(-) > > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c > index 07e394dfccc1..b63347c8bf5d 100644 > --- a/drivers/iommu/intel/iommu.c > +++ b/drivers/iommu/intel/iommu.c > @@ -3056,14 +3056,7 @@ static bool dmar_ats_supported(struct pci_dev *dev, struct intel_iommu *iommu) > dev = pci_physfn(dev); > satcu = dmar_find_matched_satc_unit(dev); > if (satcu) > - /* > - * This device supports ATS as it is in SATC table. > - * When IOMMU is in legacy mode, enabling ATS is done > - * automatically by HW for the device that requires > - * ATS, hence OS should not enable this device ATS > - * to avoid duplicated TLB invalidation. > - */ > - return !(satcu->atc_required && !sm_supported(iommu)); > + return true; > > for (bus = dev->bus; bus; bus = bus->parent) { > bridge = bus->self; -- Regards, Yi Liu