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Peter Anvin" , Tony Luck , "Peter Zijlstra (Intel)" , Paolo Bonzini , Tom Lendacky , David Rientjes , Sean Christopherson Subject: Re: [RFC Part2 PATCH 01/30] x86: Add the host SEV-SNP initialization support To: Dave Hansen , linux-kernel@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org, linux-crypto@vger.kernel.org References: <20210324170436.31843-1-brijesh.singh@amd.com> <20210324170436.31843-2-brijesh.singh@amd.com> <696b8d42-8825-9df5-54a3-fa55f2d0f421@intel.com> <7cbafc72-f740-59b0-01f8-cd926ab7e010@amd.com> <8411ae2b-1a4a-d124-ffcb-ff351adac90e@intel.com> From: Brijesh Singh Message-ID: Date: Thu, 25 Mar 2021 12:41:21 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 In-Reply-To: <8411ae2b-1a4a-d124-ffcb-ff351adac90e@intel.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [70.112.153.56] X-ClientProxiedBy: SN6PR16CA0062.namprd16.prod.outlook.com (2603:10b6:805:ca::39) To SN6PR12MB2718.namprd12.prod.outlook.com (2603:10b6:805:6f::22) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from Brijeshs-MacBook-Pro.local (70.112.153.56) by SN6PR16CA0062.namprd16.prod.outlook.com (2603:10b6:805:ca::39) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3977.25 via Frontend Transport; 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>>>> + >>>> + if (rmptable_init()) { >>>> + setup_clear_cpu_cap(X86_FEATURE_SEV_SNP); >>>> + return 1; >>>> + } >>>> + >>>> + static_branch_enable(&snp_enable_key); >>>> + >>>> + return 0; >>>> +} >>> Could you explain a bit why 'snp_enable_key' is needed in addition to >>> X86_FEATURE_SEV_SNP? >> >> The X86_FEATURE_SEV_SNP indicates that hardware supports the feature -- >> this does not necessary means that SEV-SNP is enabled in the host. > I think you're confusing the CPUID bit that initially populates > X86_FEATURE_SEV_SNP with the X86_FEATURE bit. We clear X86_FEATURE bits > all the time for features that the kernel turns off, even while the > hardware supports it. Ah, yes I was getting mixed up. I will see if we can remove the snp_key_enabled and use the feature check. > Look at what we do in init_ia32_feat_ctl() for SGX, for instance. We > then go on to use X86_FEATURE_SGX at runtime to see if SGX was disabled, > even though the hardware supports it. > >>> For a lot of features, we just use cpu_feature_enabled(), which does >>> both compile-time and static_cpu_has(). This whole series seems to lack >>> compile-time disables for the code that it adds, like the code it adds >>> to arch/x86/mm/fault.c or even mm/memory.c. >> Noted, I will add the #ifdef  to make sure that its compiled out when >> the config does not have the AMD_MEM_ENCRYPTION enabled. > IS_ENABLED() tends to be nicer for these things. > > Even better is if you coordinate these with your X86_FEATURE_SEV_SNP > checks. Then, put X86_FEATURE_SEV_SNP in disabled-features.h, and you > can use cpu_feature_enabled(X86_FEATURE_SEV_SNP) as both a > (statically-patched) runtime *AND* compile-time check without an > explicit #ifdefs. I will try improve this in v2 and will try IS_ENABLED().