Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.32 as permitted sender) client-ip=23.128.96.32;
Date:   Thu, 7 Dec 2023 16:42:26 +0800
From:   Chao Gao <chao.gao@intel.com>
To:     "Li, Xin3" <xin3.li@intel.com>
CC:     "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kselftest@vger.kernel.org" <linux-kselftest@vger.kernel.org>,
        "seanjc@google.com" <seanjc@google.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "corbet@lwn.net" <corbet@lwn.net>,
        "kys@microsoft.com" <kys@microsoft.com>,
        "haiyangz@microsoft.com" <haiyangz@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        "Cui, Dexuan" <decui@microsoft.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>, "hpa@zytor.com" <hpa@zytor.com>,
        "vkuznets@redhat.com" <vkuznets@redhat.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@intel.com>
Subject: Re: [PATCH v1 13/23] KVM: VMX: Handle VMX nested exception for FRED
Message-ID: <ZXGFcuwwmkBlqq5s@chao-email>
References: <20231108183003.5981-1-xin3.li@intel.com>
 <20231108183003.5981-14-xin3.li@intel.com>
 <ZVMkVmBPVfaMjDTL@chao-email>
 <SA1PR11MB67348D3637C2BC6B107C5CCAA8B1A@SA1PR11MB6734.namprd11.prod.outlook.com>
 <SA1PR11MB6734EFF17E15C68AAD12A227A884A@SA1PR11MB6734.namprd11.prod.outlook.com>
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <SA1PR11MB6734EFF17E15C68AAD12A227A884A@SA1PR11MB6734.namprd11.prod.outlook.com>
MIME-Version: 1.0
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
X-Spam-Status: No, score=-0.9 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED,
	DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,
	MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE
	autolearn=unavailable autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on agentk.vger.email
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (agentk.vger.email [0.0.0.0]); Thu, 07 Dec 2023 00:42:57 -0800 (PST)

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().