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David Alan Gilbert" , tony.luck@intel.com, marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com Subject: Re: [PATCH v6 14/42] x86/sev: Register GHCB memory when SEV-SNP is active To: Borislav Petkov References: <20211008180453.462291-1-brijesh.singh@amd.com> <20211008180453.462291-15-brijesh.singh@amd.com> From: Brijesh Singh Message-ID: <47815dd4-f9ac-b141-2852-8f48c8299a5e@amd.com> Date: Thu, 4 Nov 2021 10:26:56 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MN2PR02CA0018.namprd02.prod.outlook.com (2603:10b6:208:fc::31) To SN6PR12MB2718.namprd12.prod.outlook.com (2603:10b6:805:6f::22) Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Received: from [10.236.30.107] (165.204.77.1) by MN2PR02CA0018.namprd02.prod.outlook.com (2603:10b6:208:fc::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4669.10 via Frontend Transport; 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I am thinking to add >> function to register the GHCB from the early_setup_idt() >> >> early_setup_idt() >> { >> ... >> if (IS_ENABLED(CONFIG_MEM_ENCRYPT)) >> sev_snp_register_ghcb() >> ... >> } >> >> The above will cover the APs > > That will cover the APs during early boot as that is being called from > asm. > >> and for BSP case I can call the same function just after the final IDT >> is loaded > > Why after and not before? > I just looked at load_current_idt() and we should not get #VC before loading the new idt, so, its safe to do is before. >> cpu_init_exception_handling() >> { >> ... >> ... >> /* Finally load the IDT */ >> load_current_idt(); >> >> if (IS_ENABLED(CONFIG_MEM_ENCRYPT)) >> sev_snp_register_ghcb() >> >> } > > That is also called on the APs - not only the BSP. trap_init() calls it > from start_kernel() which is the BSP and cpu_init_secondary() calls it > too, which is ofc the APs. > > I guess that should be ok since you're calling the same function from > both but WTH do I know... > For AP case, we will be registering the same GHCB GPA twice, that should not be an issue. The GHCB spec does not restrict us on registering the GPA twice. Of course, the current patch does not suffer with it. Let me know your preference. thanks