linux-kernel - Re: [PATCH 0/8] KVM: x86: Fix ICR handling when x2AVIC is active

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Message-ID: <Zpr7bRMdinPsPWBU@google.com>
Date: Fri, 19 Jul 2024 16:49:01 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Maxim Levitsky <mlevitsk@...hat.com>, Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: Re: [PATCH 0/8] KVM: x86: Fix ICR handling when x2AVIC is active

On Fri, Jul 19, 2024, Sean Christopherson wrote:
> I made the mistake of expanding my testing to run with and without AVIC
> enabled, and to my surprise (wow, sarcasm), x2AVIC failed hard on the
> xapic_state_test due to ICR issues.
> 
> AFAICT, the issue is that AMD splits the 64-bit ICR into the legacy ICR
> and ICR2 fields when storing the ICR in the vAPIC (apparently "it's a
> single 64-bit register" is open to intepretation).  Aside from causing
> the selftest failure and potential live migration issues, botching the
> format is quite bad, as KVM will mishandle incomplete virtualized IPIs,
> e.g. generate IRQs to the wrong vCPU, drop IRQs, etc.
> 
> Patch 1 fixes are rather annoying wart where the xapic_state *deliberately*
> skips reserved bit tests to work around a KVM bug.  *sigh*
> 
> I couldn't find anything definitive in the APM, my findings are based on
> testing on Genoa.
>  
> Sean Christopherson (8):
>   KVM: x86: Enforce x2APIC's must-be-zero reserved ICR bits
>   KVM: x86: Move x2APIC ICR helper above kvm_apic_write_nodecode()
>   KVM: x86: Re-split x2APIC ICR into ICR+ICR2 for AMD (x2AVIC)
>   KVM: selftests: Open code vcpu_run() equivalent in guest_printf test
>   KVM: selftests: Report unhandled exceptions on x86 as regular guest
>     asserts
>   KVM: selftests: Add x86 helpers to play nice with x2APIC MSR #GPs
>   KVM: selftests: Skip ICR.BUSY test in xapic_state_test if x2APIC is
>     enabled
>   KVM: selftests: Test x2APIC ICR reserved bits

Gah, ignore this version, I managed to hit send in the middle of a rebase and
left off two patches.  I'll post a v2 to minimize confusion.