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Wed, 11 Sep 2024 22:55:45 +0000 Message-ID: Date: Thu, 12 Sep 2024 10:55:39 +1200 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 09/21] KVM: TDX: Retry seamcall when TDX_OPERAND_BUSY with operand SEPT To: "Edgecombe, Rick P" , "seanjc@google.com" CC: "Yao, Yuan" , "linux-kernel@vger.kernel.org" , "isaku.yamahata@gmail.com" , "Zhao, Yan Y" , "pbonzini@redhat.com" , "kvm@vger.kernel.org" , "nik.borisov@suse.com" , "dmatlack@google.com" References: <20240904030751.117579-1-rick.p.edgecombe@intel.com> <20240904030751.117579-10-rick.p.edgecombe@intel.com> <6449047b-2783-46e1-b2a9-2043d192824c@redhat.com> <72ef77d580d2f16f0b04cbb03235109f5bde48dd.camel@intel.com> <8618bce9-8c76-4048-8264-dfd6afc82bc6@intel.com> <5f7ee34ca34bdfcc9bf8644b66d05b10cc2d42af.camel@intel.com> Content-Language: en-US From: "Huang, Kai" In-Reply-To: <5f7ee34ca34bdfcc9bf8644b66d05b10cc2d42af.camel@intel.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SJ0PR03CA0009.namprd03.prod.outlook.com (2603:10b6:a03:33a::14) To BL1PR11MB5978.namprd11.prod.outlook.com (2603:10b6:208:385::18) 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: BL1PR11MB5978:EE_|PH7PR11MB7551:EE_ X-MS-Office365-Filtering-Correlation-Id: 13a672c0-6405-4dc0-a198-08dcd2b4defe X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016; 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A sept locking related busy, maybe. But there are other > things going on that return BUSY. I thought we are talking about SEPT locking here. For BUSY in general yeah it tries to grab other locks too (e.g., share lock of TDR/TDCS/TDVPS etc) but those are impossible to contend in the current KVM TDX implementation I suppose? Perhaps we need to look more to make sure. > >> A normal EPT violation _COULD_ mean >> mitigation is already active, but AFAICT we don't have a way to tell >> that in the EPT violation. >> >>> and can KVM rely on HOST_PRIORITY to be set if KVM >>> runs afoul of the zero-step mitigation? >> >> I think HOST_PRIORITY is always set if SEPT SEAMCALLs fails with BUSY. > > What led you to think this? It seemed more limited to me. I interpreted from the spec (chapter 18.1.4 Concurrency Restrictions with Host Priority). But looking at the module public code, it seems only when the lock can be contended from the guest the HOST_PRIORITY will be set when host fails to grab the lock (see acquire_sharex_lock_hp_ex() and acquire_sharex_lock_hp_sh()), which makes sense anyway.