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Fri, 4 Sep 2026 20:59:37 +0000 Date: Fri, 4 Sep 2026 13:59:35 -0700 From: Peter Fang To: Tony Lindgren CC: Xiaoyao Li , Dave Hansen , Kiryl Shutsemau , "Rick Edgecombe" , Kuppuswamy Sathyanarayanan , Thomas Gleixner , Ingo Molnar , Borislav Petkov , , "H. Peter Anvin" , , , , Binbin Wu Subject: Re: [PATCH v3 4/4] virt: tdx-guest: Allocate Quote buffer dynamically Message-ID: References: <20260729122939.1340412-1-peter.fang@intel.com> <20260729122939.1340412-5-peter.fang@intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: BY5PR04CA0020.namprd04.prod.outlook.com (2603:10b6:a03:1d0::30) To CH3PR11MB435924.namprd11.prod.outlook.com (2603:10b6:610:34a::8) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH3PR11MB435924:EE_|MN2PR11MB4694:EE_ X-MS-Office365-Filtering-Correlation-Id: 1bbf3e59-0876-4d95-fe34-08df0ac76e36 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|23010399003|376014|7416014|1800799024|4143699003|56012099006|10067099003|11063799006|22082099003|18002099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH3PR11MB435924.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(366016)(23010399003)(376014)(7416014)(1800799024)(4143699003)(56012099006)(10067099003)(11063799006)(22082099003)(18002099003);DIR:OUT;SFP:1101; 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This size used to be fixed at 128 KB. > > > > > > The guest driver's Quote buffer is shared with the host VMM. The current > > > fixed size may be too small for Quotes using schemes such as > > > post-quantum cryptography (PQC), where larger certificate chains can > > > increase the Quote size significantly. > > > > > > Allocate the Quote buffer based on the reported limit. This avoids > > > wasting memory on platforms that do not require larger Quotes. Older > > > platforms fall back to the default 128 KB buffer. > > > > I think we need to justify why using the value reported by TDX module > > (i.e., QUOTE_MAX_SIZE) is safe. > > > > From "Intel TDX Module Extension for Quoting" spec, > > > > QUOTE_MAX_SIZE that specifies the maximum size of the buffer that must be > > allocated to contain the Intel TDX Quote received from Intel TDX Module. > > > > So, TDX module only guarantees that QUOTE_MAX_SIZE is big enough to hold > > the quote that is generated by the TDX module. But for the current tdx > > guest driver, it doesn't know how host will generate the quote. Host can > > generate the SGX-based quote and we need to justify the QUOTE_MAX_SIZE will > > be enough for such case. Thanks for pointing this out. I confirmed with the TDX security folks. The reported QUOTE_MAX_SIZE covers all possible quote types on the platform. If GetQuote gets routed to SGX and QUOTE_MAX_SIZE is too small for that, it's a TDX module bug. I'll add a comment and update the changelog. > > And can we assume the TDX module provided size does not change after init > with a TDX module update? Yep, it's safe to assume that.