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client-ip=165.204.84.17; helo=satlexmb07.amd.com; pr=C Received: from satlexmb07.amd.com (165.204.84.17) by BN3PEPF0000B074.mail.protection.outlook.com (10.167.243.119) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.181.6 via Frontend Transport; Wed, 1 Jul 2026 16:39:40 +0000 Received: from satlexmb10.amd.com (10.181.42.219) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.41; Wed, 1 Jul 2026 11:39:40 -0500 Received: from satlexmb07.amd.com (10.181.42.216) by satlexmb10.amd.com (10.181.42.219) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.41; Wed, 1 Jul 2026 11:39:40 -0500 Received: from [172.31.184.125] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server id 15.2.2562.41 via Frontend Transport; Wed, 1 Jul 2026 11:39:29 -0500 Message-ID: <8477525d-55ad-4fc4-b7c6-05bab3d7a861@amd.com> Date: Wed, 1 Jul 2026 22:09:28 +0530 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 3/6] x86/sev: Disable CPU hotplug while SNP is active To: Jethro Beekman , Ashish Kalra , , , , , , , , , , , , CC: , , , , , , , , , , , , , , , , , , , , References: <205a5259f9fd353dc0ca6b00565c8175a96768c7.1782841284.git.ashish.kalra@amd.com> <80f3f279-d70e-44d7-a179-c52068115e46@fortanix.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <80f3f279-d70e-44d7-a179-c52068115e46@fortanix.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: uD9BHyKly7gaZ4fFClXwFgLBsEcUPLMvK65o5akj8p+wMyTDhMDLs7cXJrup+yt/dC1XCC2YgzK9w2pMqAy67CoCLh3khFV1v3woFE2S8LlF/gN+xbmELP3WKhj1tv3hXuhHOw/QmC8Bf2Wcakz8bugXQySrC7R2/F0OXl2IMLtICzefz1RmaAF/9A/xeyQKL0xuACitQx7rkwgA6boeC/uiwZpENrJVfjO58h31wvghORwTEk4wSaDhGrY7bmIRMUOY8g5+yfVQfJlDqKcX4vCNzSMsQrcFwGVdnm21QJhAUtgB5zx0JV+f+75yJ911UeKVYVxLhNwVOVRVaX/DHgL29D5JWdWk65fYbzPqzCJLcI4YwavzjhgL3t1g5H0VdEsOzp+XzdItxe5akzFSjRb87xXMgfSBYswOuZLbF4rEs3hYnHQ7Fnt+3l7QofxI X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Jul 2026 16:39:40.8085 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: befb62dd-f114-427e-2abe-08ded78f591a X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN3PEPF0000B074.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB6387 Hello Jethro, On 7/1/2026 3:10 PM, Jethro Beekman wrote: > I don't believe my concern has been addressed > > https://lore.kernel.org/lkml/0df3b665-3a9c-4c46-a7aa-14388e8e1577@fortanix.com/ Quoting your question: > I think this is too broad. If I have a hypervisor that supports SNP > virtualization, a (non-confidential) L1 guest running Linux should > still support CPU hotplug while also running confidential L2 guests. Ashish, Tom, correct me if I'm wrong, but I don't think KVM exposes SNP support to L1, at least as per https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kvm/cpuid.c?h=v7.2-rc1#n1221 and only SNP initialization disables hotplug - not the other variants. L1, running a confidential guest (SEV/SEV-ES) should still be able to support hotplug since it doesn't go through SNP init. Only the base hypervisor can setup the RMP tables and go through snp_prepare(). Also bsp_determine_snp() should clear CC_ATTR_HOST_SEV_SNP if it detects X86_FEATURE_HYPERVISOR so I don't see how this can be a problem for hotplug in L1. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/cpu/amd.c?h=v7.2-rc1#n368 -- Thanks and Regards, Prateek