Message-ID: <f5dad9e6-9824-ede1-e208-0e14c163a4f6@amd.com>
Date:   Fri, 17 Feb 2023 13:26:08 +0530
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101
 Thunderbird/102.7.2
Subject: Re: [PATCH v2 07/11] KVM: x86: add a delayed hardware NMI injection
 interface
To:     Sean Christopherson <seanjc@google.com>
Cc:     Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org,
        Sandipan Das <sandipan.das@amd.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        Jiaxi Chen <jiaxi.chen@linux.intel.com>,
        Babu Moger <babu.moger@amd.com>, linux-kernel@vger.kernel.org,
        Jing Liu <jing2.liu@intel.com>,
        Wyes Karny <wyes.karny@amd.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>
References: <20221129193717.513824-1-mlevitsk@redhat.com>
 <20221129193717.513824-8-mlevitsk@redhat.com> <Y9mWFlGdzoa8ZDW7@google.com>
 <a59505b3-5405-0409-bbf1-34466932c2c1@amd.com> <Y+PIdJZtCsGH2Sw3@google.com>
 <2b5994e2-15ba-dd57-285c-fb33827a5275@amd.com> <Y+1f/En6rvqoe6st@google.com>
 <Y+13N/Ky19VK0rzq@google.com>
Content-Language: en-US
From:   Santosh Shukla <santosh.shukla@amd.com>
In-Reply-To: <Y+13N/Ky19VK0rzq@google.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?a3U4K21rL09nKzZ6SHFPZDNQY293QmR1SVF2YW5zejJmdEt4bVFWYTZnZkNE?=
 =?utf-8?B?R3BtUHNKbnNxRUVQS2lKenRLb3ZjMVo3bDlXaGgxS2YxdXB3WEdiNzVSalYv?=
 =?utf-8?B?Uk8zWnNQY004SFBxMk0zN2pjMzFqamZXaEFGdU1qb2RyRE83ak1yc2o4bTJo?=
 =?utf-8?B?TUZROEY5Yjl3c3ZpcGo0MXA2MWxlTkE2eDlvL3g4Q2hUZVVFU2dvdTA0QUVU?=
 =?utf-8?B?N2svME5EVUdxY3M2YTlDVjZha0hKWVNrT2xSMEpNSWdQNU5iSzBOcXFjcWVV?=
 =?utf-8?B?Y0h6M1B2ZklObkNITE5wM3JwTWtLZjZMSlFkaU1ENlR6OGsrQ2IvUHl5RHUx?=
 =?utf-8?B?MXFEZmJZZVpPNDZtYTNGZXd0MDA4SXdLNWkrd25VZmMwTStSSzJLd1VQNHlZ?=
 =?utf-8?B?T0NrVjlBTFdpSkJOcDFmU3N5SUk1S1IwSk1YeDh0VjRXMzltK2tNSmhpaEht?=
 =?utf-8?B?MHczaEp6NjdBb05VUE5lRzA0Y3VIdEZCZitlNGFZM3lBVHFodDhFeGhnVWxu?=
 =?utf-8?B?cXFJMHZkS3dLcXFhUGVKVi9NbG5hYmFkdUdqOGRTbHFwTmhjek5naG1ycmZ0?=
 =?utf-8?B?eEJYQklXOWJjUU92STlKVThQTnRZdHJTTHN2aUh4WGo3RXVkQmI2TlhFSHgv?=
 =?utf-8?B?WmJjWFRUZDBPTVpmK2ZMNUJ4MXJmVW1FVzhmMVdMaFJtSXlBQ3VHUlpYNjh0?=
 =?utf-8?B?S2htajhXelNRNWRJRnRERjQ4M3oxVTFRMEloWkV5WDJUSHpNOHUyTUdqWjBp?=
 =?utf-8?B?ZmdSSHZzQm1Xc0xYd1ZiUUlybUlLWGhhOVBncHlxQWVnTGRiUWxEUFZzRGZY?=
 =?utf-8?B?NWp3bEJxS2RySVI1RlVIcDdyTkRCMW45cGNvclRzY1RPTitMN3lPVm13MFFU?=
 =?utf-8?B?VHdYN3VwMTdPTXVaeTlWcC8xaVF4WmtXKzcwWDg1MDBhZzNJOWxTU25DMTB5?=
 =?utf-8?B?Q1ZMNWxPU3NTVmQ1cnd1dEg3eUZ6N3IrT3BKbUJEMng2Q3pmb2V4UnVDbUdM?=
 =?utf-8?B?NXhlOXlKOFJ4Nk9pUEpGbGlNUURaN0l5MVZscUdHaHRaWkJJZkl2T0pzNkw4?=
 =?utf-8?B?bzFRNk1rREVqdnNkdzNXYnJ1R0pVL1BaOFVwT2hYalgvY0pySzh6bDVYYUps?=
 =?utf-8?B?TUJQdDRCYjczaktRREpTYUhldVRpU0RBYjZxbmJDZ29CT056YW1GOUoyQjVP?=
 =?utf-8?B?NGJiYSt6bG5VLzltSjE0cFlieEVLWEhFdXlORWhlNXVNZTRWdXVvdEREa25R?=
 =?utf-8?B?MnlMYnZhVzdOYU9wRHQ1cS9YaGkxS1BmbFNSd05mZUhVOUhmemV4SHFCaldt?=
 =?utf-8?B?WHlPNEQ3bS9TcXBWeWhFVUh2VWQ1ZDJLcnA4Si9JV3NocUU2NTFMOEVMWFFH?=
 =?utf-8?B?c3VoSDFRM2xTazB4SGZKN0p6ampkZ2w0QXdGU0MrYmJoVmxlS1lKWG1Ba3Fn?=
 =?utf-8?B?bHFLczJCaTk5SDRvU0lFWEl5VlU5U3B6Z1VtQlNJVUhYYTVadkc4cHdsbVVG?=
 =?utf-8?B?b21CUFNqMDhyU2c5c2xmUHVjdTV3dEdhU3piUWJ5MHR0dVFkdVpsalJNT1hH?=
 =?utf-8?B?TEpjMXIzMXQrTjE2eVhrN2NwVUx0LyttZkc0QjVMRzNlZU1qUldTNnRnZmw2?=
 =?utf-8?B?MzkzNWtDbEx3SEcxZHlzeVZMSnNuZ0NRaldxTHRIRmJMZnBwRisrVUlDem5Y?=
 =?utf-8?B?VnZFcFpZaFJJTzM0T0twbzFkZlBlY0hrZE5NWHBtWlovWm55QzFIUGtnQ3ox?=
 =?utf-8?B?c2JUS2tTc1BiYzBKUEhGY202blYvZXZaSy9jWFIzVHh3aTk0WXNyckk2Yy93?=
 =?utf-8?B?UVEyMmg2eFF6UUtjM2RSYnpNMFM4a0xWTlNJTkxCVWxka3JKRDRKM1BtSkJC?=
 =?utf-8?B?KzVPeDgyZVVpVGlldnBtRDJvZGJ2TXBoMHYwTmtvcFZ6TFpJS21TeVk1UDdx?=
 =?utf-8?B?Nm5IZmRJN0xrVFE4Tmg1VVpGVGpzMjVnUlZrQVBobXZseFJjWVJNMVJSOHJE?=
 =?utf-8?B?VmkvV0FCOXhicjUvaUVJU0UxQ2E4S0hiNk5wbHp5aDhlUFJ5WVNUS2g1d1E2?=
 =?utf-8?B?cE9lZjhuRkUxL3ZBeGhSMmExS2IwWmdYc3BkclBtQm5sRU9zY0ZCMGpIQUJC?=
 =?utf-8?Q?NP/v3YPH/XL3Naip7fLX7C1CJ?=
X-OriginatorOrg: amd.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 3f8ecb4a-d0be-44ef-cde8-08db10bc8906
X-MS-Exchange-CrossTenant-AuthSource: CY5PR12MB6323.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Feb 2023 07:56:54.3453
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: KMsSlNMibtzZiwwZjcVt/cIXtbHVOaJ/SO1Yqk8Q2pjcumKW6IGUfW/FuFUZ0yOnnXg6LQtLl0MxE2oc1FpzRg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW6PR12MB8706
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 2/16/2023 5:52 AM, Sean Christopherson wrote:
> On Wed, Feb 15, 2023, Sean Christopherson wrote:
>> On Tue, Feb 14, 2023, Santosh Shukla wrote:
>>> "
>>> V_NMI_MASK: Indicates whether virtual NMIs are masked. The processor will set V_NMI_MASK
>>> once it takes the virtual NMI. V_NMI_MASK is cleared when the guest successfully completes an
>>> IRET instruction or #VMEXIT occurs while delivering the virtual NMI
>>> "
>>>
>>> In my initial implementation I had changed V_NMI_MASK for the SMM scenario [1],
>>> This is also not required as HW will save the V_NMI/V_NMI_MASK on 
>>> SMM entry and restore them on RSM.
>>>
>>> That said the svm_{get,set}_nmi_mask will look something like:
> 
> ...
> 
>>>  static void svm_set_nmi_mask(struct kvm_vcpu *vcpu, bool masked)
>>>  {
>>>         struct vcpu_svm *svm = to_svm(vcpu);
>>>
>>> +       if (is_vnmi_enabled(svm))
>>> +               return;
>>> +
>>>         if (masked) {
>>>                 svm->nmi_masked = true;
>>>                 svm_set_iret_intercept(svm);
>>>
>>> is there any inputs on above approach?
>>
>> What happens if software clears the "NMIs are blocked" flag?  If KVM can't clear
>> the flag, then we've got problems.  E.g. if KVM emulates IRET or SMI+RSM.  And I
>> I believe there are use cases that use KVM to snapshot and reload vCPU state,
>> e.g. record+replay?, in which case KVM_SET_VCPU_EVENTS needs to be able to adjust
>> NMI blocking too.
> 
> Actually, what am I thinking.  Any type of state save/restore will need to stuff
> NMI blocking.  E.g. live migration of a VM that is handling an NMI (V_NMI_MASK=1)
> _and_ has a pending NMI (V_NMI=1) absolutely needs to set V_NMI_MASK=1 on the dest,
> otherwise the pending NMI will get serviced when the guest expects NMIs to be blocked.

Sure, Make sense. Will include V_NMI_BLOCKING_MASK set/clear in svm_set_nmi_mask() in v3
and will soon share patches for review.

Thanks.