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Bae" Subject: Re: [PATCH v8 03/20] KVM: x86: Support APX state for XSAVE ABI To: CC: References: <20260930210750.1487547-1-chang.seok.bae@intel.com> <20260930210750.1487547-4-chang.seok.bae@intel.com> <20260930215732.4F6A51F00898@smtp.kernel.org> Content-Language: en-US In-Reply-To: <20260930215732.4F6A51F00898@smtp.kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY1P220CA0007.NAMP220.PROD.OUTLOOK.COM (2603:10b6:a03:59d::13) To DS0PR11MB7925.namprd11.prod.outlook.com (2603:10b6:8:f8::18) 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: DS0PR11MB7925:EE_|LVXPR11MB9708:EE_ X-MS-Office365-Filtering-Correlation-Id: e795b5c3-e128-4f0a-0e95-08df1ffa0fbf X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|366016|1800799024|376014|18002099003|22082099003|56012099006|4143699003|10067099003|11063799006; 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>> + >> + if (!(xstate->xsave.header.xfeatures & XFEATURE_MASK_APX)) >> + return 0; > > [Severity: High] > Does this early return leave stale values in the APX registers instead of > initializing them to zero? The comment repeats the concern from: https://lore.kernel.org/kvm/761b969a-2d2c-4233-b3ed-2f0f35f04864@intel.com/ I think my previous comment explains the intended behavior: This matches the existing XSAVE uABI semantics. XSTATE_BV specifies which state components are being updated. If userspace wants to zero the APX state, it must include the APX bit in XSTATE_BV; omitting the bit means "leave this component unchanged", just like the generic XSAVE copy path. Thanks, Chang