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Fri, 11 Apr 2025 17:37:41 +0000 Message-ID: <7d1330e3-a0f0-4a4c-a487-46304822e0fd@intel.com> Date: Fri, 11 Apr 2025 12:37:33 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/5] x86/tdx: tdx_mcall_get_report0: Return -EBUSY on TDCALL_OPERAND_BUSY error To: Dan Williams , "Kirill A. Shutemov" , Dave Hansen , Thomas Gleixner , Ingo Molnar , Borislav Petkov , , "H. Peter Anvin" CC: , , "Dionna Amalie Glaze" , Guorui Yu , James Bottomley , Dan Middleton , Mikko Ylinen , Sathyanarayanan Kuppuswamy References: <20250407-tdx-rtmr-v3-0-54f17bc65228@intel.com> <20250407-tdx-rtmr-v3-4-54f17bc65228@intel.com> <67f601e35845f_720529475@dwillia2-xfh.jf.intel.com.notmuch> Content-Language: en-US From: "Xing, Cedric" In-Reply-To: <67f601e35845f_720529475@dwillia2-xfh.jf.intel.com.notmuch> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR13CA0082.namprd13.prod.outlook.com (2603:10b6:a03:2c4::27) To DS7PR11MB6269.namprd11.prod.outlook.com (2603:10b6:8:97::14) Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR11MB6269:EE_|LV2PR11MB6047:EE_ X-MS-Office365-Filtering-Correlation-Id: 028410b9-0577-4033-b3e4-08dd791f8f1c 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|366016|1800799024; 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This enables the caller to retry obtaining a >> TDREPORT later if another VCPU is extending an RTMR concurrently. > > Can this not be prevented by proper locking? Otherwise this type of > collision sounds like a kernel bug, not something that should escape to > userspace. > Yes, -EBUSY should never happen with proper locking, which however is implemented in the upper layer. Similarly, -EINVAL will also indicate a kernel bug but is left for the upper layer to handle. > I.e. userspace can not reasonably know when it is safe to retry, so take > locks to ensure forward progress. tdx-guest does WARN() on errors. There are no other users of this function currently. Returning an error, however, will allow different error handling in the future (e.g., retry instead of WARN on -EBUSY).