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Thu, 22 May 2025 14:44:57 +0000 Date: Thu, 22 May 2025 22:44:41 +0800 From: Chao Gao To: Sean Christopherson CC: , , , , , , , , , , , , , Ingo Molnar , Dave Hansen , "H. Peter Anvin" , Samuel Holland , "Mitchell Levy" , Kees Cook , "Stanislav Spassov" , Eric Biggers , "Nikolay Borisov" , Oleg Nesterov , "Vignesh Balasubramanian" Subject: Re: [PATCH v7 1/6] x86/fpu/xstate: Differentiate default features for host and guest FPUs Message-ID: References: <20250512085735.564475-1-chao.gao@intel.com> <20250512085735.564475-2-chao.gao@intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: KU0P306CA0080.MYSP306.PROD.OUTLOOK.COM (2603:1096:d10:2b::16) To CH3PR11MB8660.namprd11.prod.outlook.com (2603:10b6:610:1ce::13) 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: CH3PR11MB8660:EE_|BL3PR11MB6364:EE_ X-MS-Office365-Filtering-Correlation-Id: 656fd8e8-9940-4da3-da8d-08dd993f38c8 X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|366016; 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>> } >> >> +static void __init init_default_features(u64 kernel_max_features, u64 user_max_features) >> +{ >> + u64 kfeatures = kernel_max_features; >> + u64 ufeatures = user_max_features; >> + >> + /* Default feature sets should not include dynamic xfeatures. */ >> + kfeatures &= ~XFEATURE_MASK_USER_DYNAMIC; >> + ufeatures &= ~XFEATURE_MASK_USER_DYNAMIC; >> + >> + fpu_kernel_cfg.default_features = kfeatures; >> + fpu_user_cfg.default_features = ufeatures; >> + >> + guest_default_cfg.features = kfeatures; >> +} >> + >> /* >> * Enable and initialize the xsave feature. >> * Called once per system bootup. >> @@ -854,12 +873,8 @@ void __init fpu__init_system_xstate(unsigned int legacy_size) >> fpu_user_cfg.max_features = fpu_kernel_cfg.max_features; >> fpu_user_cfg.max_features &= XFEATURE_MASK_USER_SUPPORTED; >> >> - /* Clean out dynamic features from default */ >> - fpu_kernel_cfg.default_features = fpu_kernel_cfg.max_features; >> - fpu_kernel_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC; >> - >> - fpu_user_cfg.default_features = fpu_user_cfg.max_features; >> - fpu_user_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC; >> + /* Now, given maximum feature set, determine default values */ >> + init_default_features(fpu_kernel_cfg.max_features, fpu_user_cfg.max_features); > >Passing in max_features is rather odd. I assume the intent is to capture the >dependencies, but that falls apart by the end of series as the guest features >are initialized as: > > guest_default_cfg.features = kfeatures | xfeatures_mask_guest_supervisor(); > >where xfeatures_mask_guest_supervisor() sneakily consumes fpu_kernel_cfg.max_features, >the very field this patch deliberately avoids consuming directly. > > static inline u64 xfeatures_mask_guest_supervisor(void) > { > return fpu_kernel_cfg.max_features & XFEATURE_MASK_GUEST_SUPERVISOR; > } > Indeed, it is odd. And your suggestion looks good to me. Thanks. I will fix this and the comment issue you pointed out and post a new version.