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Thu, 7 Dec 2023 08:42:40 +0000 Date: Thu, 7 Dec 2023 16:42:26 +0800 From: Chao Gao To: "Li, Xin3" CC: "kvm@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-hyperv@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "seanjc@google.com" , "pbonzini@redhat.com" , "corbet@lwn.net" , "kys@microsoft.com" , "haiyangz@microsoft.com" , "wei.liu@kernel.org" , "Cui, Dexuan" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "vkuznets@redhat.com" , "peterz@infradead.org" , "Shankar, Ravi V" Subject: Re: [PATCH v1 13/23] KVM: VMX: Handle VMX nested exception for FRED Message-ID: References: <20231108183003.5981-1-xin3.li@intel.com> <20231108183003.5981-14-xin3.li@intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: SI2PR01CA0050.apcprd01.prod.exchangelabs.com (2603:1096:4:193::21) To CH3PR11MB8660.namprd11.prod.outlook.com (2603:10b6:610:1ce::13) 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: CH3PR11MB8660:EE_|IA1PR11MB7854:EE_ X-MS-Office365-Filtering-Correlation-Id: 03f54bcb-62fe-4813-8a0b-08dbf700781e 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; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?m+FzD0dX7jSCYMLPwVL6kA4XWP4UPhv0hEo7W9x086U4FRWX5aMHxxEjKKlD?= =?us-ascii?Q?P93nHodfmsCpaEQvpwjnwPKWP+JT0LxmS3QbXXWeI5XJcBOosmtlttavr6AQ?= =?us-ascii?Q?u+TMkSWHoTK7lLivru4ekQHU0cQFhOupCXaDFKdJ2j/62G/qDYjpBDD3J85m?= =?us-ascii?Q?kRa/m2itUhe1KRkwjaJBTJcU8WA+XaFrn6dzcR+OfO7qjNFEyADReHMHsaR+?= =?us-ascii?Q?nfGkBMPMusul4BSVb57H4xeaol4unYVLV46waFYV4bSojUHaWgUI7m98by05?= =?us-ascii?Q?C3rZulEE8DU8Z90RjGOyRahGg7oaAXkBGkXvrLTqdU8edryg7RT0UgViygyl?= =?us-ascii?Q?JngZF+bLZrtB0EXhlKIpJah1+or4Ipb/V/nT3Fr3b9xnC5krgxw+D7X43y3Q?= =?us-ascii?Q?+gTnDaKJ6Fnpk7E8KvIvq03c4gdpHbu7JXyySrKDbIfzwcVCDb/rcUrGU/Xb?= =?us-ascii?Q?67Hd9sH1WhIKb58/tW8ldmlg+NOdsCnXwYxGiCWfggWP5MToOJzNTlnLUOA1?= =?us-ascii?Q?ntiNsQNR9AYHMOD8QG+iyRVi9/xGqEZ8aEkOYlovu1G2HNx6hwwhAuvvgjlg?= =?us-ascii?Q?7XGFrilSC7XsdzAD8boM87r+pk7l4AY5COS41gxet7oc+11uOQtIFWpf/dFM?= =?us-ascii?Q?7BpNZ0jwUU1uWbAiP+ZnAUfo9OPTQ47FbsS7gA/c6ITUJSfhnFHFIN3gLCw4?= =?us-ascii?Q?SrUxmYr5s62js7ckb5sFdy1J20pyhC27MBNaR1BdMnp4ARvmxC/cZAILonDF?= =?us-ascii?Q?0R5GS75fVYoFXV0L1Y2dCHjcJObBg7ZhUVoV8XTPf6TvGF/2rPFL0NCjeNAg?= =?us-ascii?Q?oAO/OjWUhB1TeFgSPB8boTWmcNBa3rc7Isv2YFdMzPdzLctjbu6lMCK0wJKT?= =?us-ascii?Q?AWPDfTTYpJ0HGOfyXTOA96tct1q3sXNeA8nkVxdpO6vitpGXp/hZGSkLWzgr?= =?us-ascii?Q?NwDKEwdVVOvuo6s5wSplh5BQKYzVp7WMY3TUxtrnvkgsa2ZfjWv0WomxzCaR?= =?us-ascii?Q?yTh5H5K9Nh76O1Gvs/eYd4n7SGWMO+CWqLiDaUkt5A+01bGhKEsu7QpUmDzI?= =?us-ascii?Q?DPYSkFI4uqZ01L6E87Y6qYq+GKf9G/kTaOlss2h0Uy8AL6qwNCCE3UVl8Eby?= =?us-ascii?Q?P+LOMGJvD93PialelM5gHmoRravxcoX8hEmpGsLHqUKB9OPfDOZNDuN4bVBq?= =?us-ascii?Q?tjTVUPLghHbXheFGUwROJkVBcUKLzemTG85o/6R2+m4HG562d90WqJDhMkye?= =?us-ascii?Q?BsSkmxwLftOT2l0TOzFzER78B0yf42Xz9xwGwEpc4AMkT9J8bCZTAq6aEYl2?= =?us-ascii?Q?3L2Hgn7hS+v17X4DIIfU01k8ZBTZLsWQbgCxrYbTquea7m7iK8yN83h12/SZ?= =?us-ascii?Q?ZLeKRaofYcv3cqsTsbxliMBJrJT3t1kYp+DBlLBDlp8MqjT9N7+iGhmV1BtE?= =?us-ascii?Q?Z1FYWbpeCdxnA5NjehWTkpMwGKc/xxcBtuPK/HINdJ6/AFeeu98Fnh0toXnU?= =?us-ascii?Q?KLtolLwgIYSmLHRuJCMUQ1h7xqsm6Udn1XkFUkkNZt6pby3wHbTu4+QZLB+x?= =?us-ascii?Q?Nv7Lq3mmF7ESph7Fl3EdAJbH+y/23qhLA1A/JbgJ?= X-MS-Exchange-CrossTenant-Network-Message-Id: 03f54bcb-62fe-4813-8a0b-08dbf700781e X-MS-Exchange-CrossTenant-AuthSource: CH3PR11MB8660.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Dec 2023 08:42:39.2483 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: xTYNz6Ug9m7T6FUcx7NEyQYtQ/dBSLDDfKDLSsljypZDTamECOcuHhoAPoE5p7aYJhURwNCAqsUVzaL0hp+xeA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR11MB7854 X-OriginatorOrg: intel.com On Wed, Dec 06, 2023 at 04:37:39PM +0800, Li, Xin3 wrote: >> Subject: RE: [PATCH v1 13/23] KVM: VMX: Handle VMX nested exception for FRED >> >> > >+ if (idt_vectoring_info & >> VECTORING_INFO_DELIVER_CODE_MASK) >> > >+ kvm_requeue_exception_e(vcpu, vector, >> > vmcs_read32(error_code_field), >> > >+ idt_vectoring_info & >> > INTR_INFO_NESTED_EXCEPTION_MASK); >> > >+ else >> > >+ kvm_requeue_exception(vcpu, vector, >> > >+ idt_vectoring_info & >> > INTR_INFO_NESTED_EXCEPTION_MASK); >> > >> > Exiting-event identification can also have bit 13 set, indicating a >> > nested exception encountered and caused VM-exit. when reinjecting the >> > exception to guests, kvm needs to set the "nested" bit, right? I >> > suspect some changes to e.g., handle_exception_nmi() are needed. >> >> The current patch relies on kvm_multiple_exception() to do that. But TBH, I'm >> not sure it can recognize all nested cases. I probably should revisit it. > >So the conclusion is that kvm_multiple_exception() is smart enough, and >a VMM doesn't have to check bit 13 of the Exiting-event identification. > >In FRED spec 5.0, section 9.2 - New VMX Feature: VMX Nested-Exception >Support, there is a statement at the end of Exiting-event identification: > >(The value of this bit is always identical to that of the valid bit of >the original-event identification field.) > >It means that even w/o VMX Nested-Exception support, a VMM already knows >if an exception is a nested exception encountered during delivery of >another event in an exception caused VM exit (exit reason 0). This is >done in KVM through reading IDT_VECTORING_INFO_FIELD and calling >vmx_complete_interrupts() immediately after VM exits. > >vmx_complete_interrupts() simply queues the original exception if there is >one, and later the nested exception causing the VM exit could be cancelled >if it is a shadow page fault. However if the shadow page fault is caused >by a guest page fault, KVM injects it as a nested exception to have guest >fix its page table. > >I will add comments about this background in the next iteration. is it possible that the CPU encounters an exception and causes VM-exit during injecting an __interrupt__? in this case, no __exception__ will be (re-)queued by vmx_complete_interrupts().