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Tue, 29 Sep 2026 16:03:31 +0000 Date: Tue, 29 Sep 2026 09:03:28 -0700 From: Peter Fang To: "Edgecombe, Rick P" CC: "kvm@vger.kernel.org" , "Li, Xiaoyao" , "linux-coco@lists.linux.dev" , "Hansen, Dave" , "dave.hansen@linux.intel.com" , "kas@kernel.org" , "seanjc@google.com" , "mingo@redhat.com" , "linux-kernel@vger.kernel.org" , "binbin.wu@linux.intel.com" , "tony.lindgren@linux.intel.com" , "hpa@zytor.com" , "tglx@kernel.org" , "bp@alien8.de" , "Bityutskiy, Artem" , "sathyanarayanan.kuppuswamy@linux.intel.com" , "x86@kernel.org" Subject: Re: [PATCH v5 4/6] virt: tdx-guest: Add a helper for the Quote buffer size Message-ID: References: <20260928100913.2265687-1-peter.fang@intel.com> <20260928100913.2265687-5-peter.fang@intel.com> <0c6bc71f-53fb-4240-83a3-c52d090044d3@intel.com> <42975a72efc3a0f96200c065cb86970e8f452625.camel@intel.com> <1d20a787ac6c51e923c96b18a8c44fe8e7dd6d0d.camel@intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1d20a787ac6c51e923c96b18a8c44fe8e7dd6d0d.camel@intel.com> X-ClientProxiedBy: SJ0PR05CA0104.namprd05.prod.outlook.com (2603:10b6:a03:334::19) To CH3PR11MB435924.namprd11.prod.outlook.com (2603:10b6:610:34a::8) 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: CH3PR11MB435924:EE_|MN2PR11MB4662:EE_ X-MS-Office365-Filtering-Correlation-Id: 93832675-2773-47d9-dc2f-08df1e43350b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|23010399003|1800799024|7416014|376014|56012099006|10067099003|11063799006|4143699003|18002099003|22082099003; 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Why is it doing what it is > > > > doing? This should also explain why it is page-aligning and caching > > > > things. > > > > > > I'm not sure it actually needs to be. It shortens the math in the places > > > where it needs to calculate the pages. And then in tdx_report_new_locked() > > > it skips zeroing the whole buffer (not sure why to zero the buffer actually. > > > Seems it > > > > I talked to the TDX security folks and this seems to be a hygiene thing. > > ??? I was also confused about the zeroing in tdx_report_new_locked(), so I asked around and the answer was "it's good practice to zero the buffer before use". So I don't think there was a security reason behind this zeroing. > > > Skipping the zeroing shouldn't pose a security risk. > > It is allocated __GFP_ZERO so today the whole thing already gets zeroed before > being set shared. After that it is a shared buffer and host can read/write it as > much as they want. Agreed.