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Sampat" Subject: Re: [PATCH v3 2/2] x86/sev: Add support to unaccept memory after hot-remove To: Kiryl Shutsemau , Dave Hansen Cc: linux-mm@kvack.org, linux-coco@lists.linux.dev, x86@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, ardb@kernel.org, akpm@linux-foundation.org, david@kernel.org, osalvador@suse.de, thomas.lendacky@amd.com, michael.roth@amd.com References: <20260128204105.508855-1-prsampat@amd.com> <20260128204105.508855-3-prsampat@amd.com> <16aa84a9-83ce-4748-bc73-ccf5cb6ce376@intel.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SN6PR05CA0024.namprd05.prod.outlook.com (2603:10b6:805:de::37) To CH3PR12MB8660.namprd12.prod.outlook.com (2603:10b6:610:177::5) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH3PR12MB8660:EE_|CY8PR12MB8338:EE_ X-MS-Office365-Filtering-Correlation-Id: a74230e5-e669-48ca-4b39-08de5f5c8334 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|366016|1800799024; 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Sampat wrote: >>> +static inline void arch_unaccept_memory(phys_addr_t start, phys_addr_t end) >>> +{ >>> + if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP)) { >>> + snp_unaccept_memory(start, end); >>> + } else { >>> + panic("Cannot unaccept memory: unknown platform\n"); >>> + } >>> +} >> >> This panic() is pretty nasty. >> >> Can't we just disable memory hotplug up front if it's: >> >> !cc_platform_has(CC_ATTR_GUEST_SEV_SNP) >> >> ? > > I don't understand SEV-SNP situation, but I don't think we need to do > anything on unplug for TDX. We should expect the unplugged memory to be > removed from SEPT. If VMM doesn't do this, it is effectively DoS and we > don't protect against DoS in CoCo. > > Converting the memory to shared will do no good for us. In that case a fall through for TDX (with a comment explaining why) and panic for rest may be the way to go? >