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b=z1qRNk42ff0gBEy4zYlErQa/u4Cv7mCx6wGIYQaWnScSGEhT75whOwhXI75KpbZzEi/ytgmuWqPs4gnsXtwlCrEYg69BYL2kCx3RDNdW8/huUC9ARcGsG21Q/OqG8a6SK6l/zyn74ka1OEjLxb8Dgd66NdcYSmIIDbB1dRWZckQ= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from DS7PR12MB5766.namprd12.prod.outlook.com (2603:10b6:8:75::12) by CH2PR12MB4119.namprd12.prod.outlook.com (2603:10b6:610:aa::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.270.15; Thu, 30 Jul 2026 11:26:45 +0000 Received: from DS7PR12MB5766.namprd12.prod.outlook.com ([fe80::222:966a:d65d:d08e]) by DS7PR12MB5766.namprd12.prod.outlook.com ([fe80::222:966a:d65d:d08e%3]) with mapi id 15.21.0270.009; Thu, 30 Jul 2026 11:26:45 +0000 Message-ID: <08f2e48e-6e98-4fde-af71-cb8cde666bdf@amd.com> Date: Thu, 30 Jul 2026 16:56:37 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] iommu/amd: Force identity mode for selected GPUs only To: Mario Limonciello , "Kuehling, Felix" , Jason Gunthorpe , "Deucher, Alexander" Cc: iommu@lists.linux.dev, joro@8bytes.org, linux-pci@vger.kernel.org, will@kernel.org, robin.murphy@arm.com, suravee.suthikulpanit@amd.com, bhelgaas@google.com, Amandeep Kaur Longia References: <20260723061548.10187-1-vasant.hegde@amd.com> <20260723061548.10187-3-vasant.hegde@amd.com> <838281e9-8ee7-433a-b06c-68675e9b285f@amd.com> <2f400c7f-eada-45e3-9079-7b5727ecb5c3@amd.com> Content-Language: en-US From: Vasant Hegde In-Reply-To: Content-Type: text/plain; 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> > -       /* > -        * Do not identity map IOMMUv2 capable devices when: > -        *  - memory encryption is active, because some of those devices > -        *    (AMD GPUs) don't have the encryption bit in their DMA-mask > -        *    and require remapping. > -        *  - SNP is enabled, because it prohibits DTE[Mode]=0. > -        */ > -       if (pdev_pasid_supported(dev_data) && > -           !cc_platform_has(CC_ATTR_MEM_ENCRYPT) && > -           !amd_iommu_snp_en) { > -               return IOMMU_DOMAIN_IDENTITY; > -       } > - >         return 0; >  } > > The flicking is reminencent of issues moving BOs between VRAM and GTT from a few > years ago. > > So I don't think it can be dropped (just) yet. Based on discussion so far in this thread and the link Mario shared earlier [1]: - We still need identity mapping for APUs. I will fine tune the patch based on the discussion in this thread. - Its fine to drop SNP check - I am still not sure its safe to drop SME check (CC_ATTR_MEM_ENCRYPT) Because here were are putting all APUs in identity mode. Commit ea68573d408f explicitly error out for RAVEN and some of the older APU platform didn't support SME. But not sure about newer ones. So I am inclined to keep SME check for now. Once this patch stabilized we can revisit the SME check? [1] https://lore.kernel.org/all/20200824105415.21000-1-joro@8bytes.org/ -Vasant