linux-kernel - Re: [PATCH 0/7] Virtual NMI feature

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Message-ID: <fd73f376-345d-6f58-987d-cca203e06cad@amd.com>
Date:   Wed, 8 Jun 2022 13:53:37 +0530
From:   "Shukla, Santosh" <santosh.shukla@....com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/7] Virtual NMI feature



On 6/7/2022 4:31 AM, Jim Mattson wrote:
> On Thu, Jun 2, 2022 at 7:26 AM Santosh Shukla <santosh.shukla@....com> wrote:
>>
>> Currently, NMI is delivered to the guest using the Event Injection
>> mechanism [1]. The Event Injection mechanism does not block the delivery
>> of subsequent NMIs. So the Hypervisor needs to track the NMI delivery
>> and its completion(by intercepting IRET) before sending a new NMI.
>>
>> Virtual NMI (VNMI) allows the hypervisor to inject the NMI into the guest
>> w/o using Event Injection mechanism meaning not required to track the
>> guest NMI and intercepting the IRET. To achieve that,
>> VNMI feature provides virtualized NMI and NMI_MASK capability bits in
>> VMCB intr_control -
>> V_NMI(11) - Indicates whether a virtual NMI is pending in the guest.
>> V_NMI_MASK(12) - Indicates whether virtual NMI is masked in the guest.
>> V_NMI_ENABLE(26) - Enables the NMI virtualization feature for the guest.
>>
>> When Hypervisor wants to inject NMI, it will set V_NMI bit, Processor will
>> clear the V_NMI bit and Set the V_NMI_MASK which means the Guest is
>> handling NMI, After the guest handled the NMI, The processor will clear
>> the V_NMI_MASK on the successful completion of IRET instruction
>> Or if VMEXIT occurs while delivering the virtual NMI.
>>
>> To enable the VNMI capability, Hypervisor need to program
>> V_NMI_ENABLE bit 1.
>>
>> The presence of this feature is indicated via the CPUID function
>> 0x8000000A_EDX[25].
>>
>> Testing -
>> * Used qemu's `inject_nmi` for testing.
>> * tested with and w/o AVIC case.
>> * tested with kvm-unit-test
>>
>> Thanks,
>> Santosh
>> [1] https://www.amd.com/system/files/TechDocs/40332.pdf
>> ch-15.20 - "Event Injection".
>>
>> Santosh Shukla (7):
>>   x86/cpu: Add CPUID feature bit for VNMI
>>   KVM: SVM: Add VNMI bit definition
>>   KVM: SVM: Add VNMI support in get/set_nmi_mask
>>   KVM: SVM: Report NMI not allowed when Guest busy handling VNMI
>>   KVM: SVM: Add VNMI support in inject_nmi
>>   KVM: nSVM: implement nested VNMI
>>   KVM: SVM: Enable VNMI feature
>>
>>  arch/x86/include/asm/cpufeatures.h |  1 +
>>  arch/x86/include/asm/svm.h         |  7 +++++
>>  arch/x86/kvm/svm/nested.c          |  8 +++++
>>  arch/x86/kvm/svm/svm.c             | 47 ++++++++++++++++++++++++++++--
>>  arch/x86/kvm/svm/svm.h             |  1 +
>>  5 files changed, 62 insertions(+), 2 deletions(-)
>>
>> --
>> 2.25.1
> 
> When will we see vNMI support in silicon? Genoa?
> 
> Where is this feature officially documented? Is there an AMD64
> equivalent of the "Intel Architecture Instruction Set Extensions and
> Future Features" manual?

Hi Jim,

A new revision of the Architecture programmers manual (APM) is slated
to be release soon and that is going to have all the details for
the above questions.

Thanks,
Santosh