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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by SN1PEPF000252A3.mail.protection.outlook.com (10.167.242.10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8489.16 via Frontend Transport; Tue, 25 Feb 2025 19:45:12 +0000 Received: from [10.236.185.178] (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Tue, 25 Feb 2025 13:45:09 -0600 Message-ID: <6c497385-6447-4d81-8d93-20c46cad29f9@amd.com> Date: Tue, 25 Feb 2025 13:45:04 -0600 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 01/10] KVM: SEV: Disable SEV-SNP support on initialization failure To: Tom Lendacky , , , , , CC: , , , , , , , , , , , , References: <20250221210200.244405-1-prsampat@amd.com> <20250221210200.244405-2-prsampat@amd.com> <88fc49a9-d801-5d8f-f156-28fa06910cd6@amd.com> <9480ce1b-2c35-499c-b60f-1c02ea9cdc16@amd.com> Content-Language: en-US From: "Pratik R. 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Sampat wrote: >> On 2/25/2025 10:41 AM, Pratik R. Sampat wrote: >>> Hi Tom, >>> >>> On 2/24/2025 3:28 PM, Tom Lendacky wrote: >>>> On 2/21/25 15:01, Pratik R. Sampat wrote: >>>>> During platform init, SNP initialization may fail for several reasons, >>>>> such as firmware command failures and incompatible versions. However, >>>>> the KVM capability may continue to advertise support for it. Export this >>>>> information to KVM and withdraw SEV-SNP support if has not been >>>>> successfully initialized. >>>> >>>> Hmmm... rather than creating a new API, can you just issue an >>>> SNP_PLATFORM_STATUS command and see if the SNP is not in the UNINIT state? >>>> >>> >>> Although reading sev->snp_initialized is probably cheaper to do, it is >>> cleaner to query the platform status. >>> >>> Querying SNP_PLATFORM_STATUS requires the pages to transition to >>> firmware-owned and back, and the helpers for it are implemented within >>> sev-dev.c. So, similar to sev_platform_status(), I'm thinking it is >>> probably better to create the snp_platform_status() API as well and use >>> that within KVM to check the state. >>> >> >> Although I am guessing the initial intent was to not have an API exposed >> at all from CCP and only make the SNP_PLATFORM_STATUS call instead? >> >> Since that may not be cleanly possible (we have helpers for page state >> conversions such as rmp_mark_pages_firmware() in ccp) without >> duplicating functionality in KVM as well, I guess the question really >> boils down to whether we export the cheaper snp_initialized() or the >> snp_platform_status() API instead? > > Taking a closer look, we do already have APIs that KVM uses to allocate > firmware pages (output pages for SNP APIs) that can be used: > snp_alloc_firmware_page() and snp_free_firmware_page(). > > I think that should be enough to use sev_do_cmd() to perform the > SEV_CMD_SNP_PLATFORM_STATUS command without exposing a new API. > Ah, I had missed that! Calling the SNP_PLATFORM_STATUS this way works. Pratik > Thanks, > Tom > >> >> Thanks again! >> Pratik