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

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Date:   Thu, 1 Jun 2023 11:04:43 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
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 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.