linux-kernel - Re: [PATCH] KVM: SVM: vNMI pending bit is V_NMI_PENDING_MASK not V_NMI_BLOCKING

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Message-ID: <0c897867-42cb-60b0-aca7-7c8136411e1a@maciej.szmigiero.name>
Date:   Thu, 1 Jun 2023 20:05:25 +0200
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Santosh Shukla <santosh.shukla@....com>, vkuznets@...hat.com,
        jmattson@...gle.com, thomas.lendacky@....com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: SVM: vNMI pending bit is V_NMI_PENDING_MASK not
 V_NMI_BLOCKING_MASK

On 1.06.2023 20:04, Sean Christopherson wrote:
> On Thu, Jun 01, 2023, Maciej S. Szmigiero wrote:
>> On 19.05.2023 17:51, Sean Christopherson wrote:
>>> On Fri, May 19, 2023, Maciej S. Szmigiero wrote:
>>>> From: "Maciej S. Szmigiero" <maciej.szmigiero@...cle.com>
>>>>
>>>> While testing Hyper-V enabled Windows Server 2019 guests on Zen4 hardware
>>>> I noticed that with vCPU count large enough (> 16) they sometimes froze at
>>>> boot.
>>>> With vCPU count of 64 they never booted successfully - suggesting some kind
>>>> of a race condition.
>>>>
>>>> Since adding "vnmi=0" module parameter made these guests boot successfully
>>>> it was clear that the problem is most likely (v)NMI-related.
>>>>
>>>> Running kvm-unit-tests quickly showed failing NMI-related tests cases, like
>>>> "multiple nmi" and "pending nmi" from apic-split, x2apic and xapic tests
>>>> and the NMI parts of eventinj test.
>>>>
>>>> The issue was that once one NMI was being serviced no other NMI was allowed
>>>> to be set pending (NMI limit = 0), which was traced to
>>>> svm_is_vnmi_pending() wrongly testing for the "NMI blocked" flag rather
>>>> than for the "NMI pending" flag.
>>>>
>>>> Fix this by testing for the right flag in svm_is_vnmi_pending().
>>>> Once this is done, the NMI-related kvm-unit-tests pass successfully and
>>>> the Windows guest no longer freezes at boot.
>>>>
>>>> Fixes: fa4c027a7956 ("KVM: x86: Add support for SVM's Virtual NMI")
>>>> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@...cle.com>
>>>
>>> Reviewed-by: Sean Christopherson <seanjc@...gle.com>
>>>
>>
>> I can't see this in kvm/kvm.git trees or the kvm-x86 ones on GitHub -
>> is this patch planned to be picked up for -rc5 soon?
>>
>> Technically, just knowing the final commit id would be sufficit for my
>> purposes.
> 
> If Paolo doesn't pick it up by tomorrow, I'll apply it and send a fixes pull
> request for -rc5.

Thanks Sean.