linux-kernel - Re: [PATCH v3] KVM: x86: Allow APICv APIC ID inhibit to be cleared

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Message-ID: <Y3es/yLTo1dXSzAF@google.com>
Date:   Fri, 18 Nov 2022 16:04:15 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Greg Edwards <gedwards@....com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH v3] KVM: x86: Allow APICv APIC ID inhibit to be cleared

On Thu, Nov 17, 2022, Greg Edwards wrote:
> Legacy kernels prior to commit 4399c03c6780 ("x86/apic: Remove
> verify_local_APIC()") write the APIC ID of the boot CPU twice to verify
> a functioning local APIC.  This results in APIC acceleration inhibited
> on these kernels for reason APICV_INHIBIT_REASON_APIC_ID_MODIFIED.
> 
> Allow the APICV_INHIBIT_REASON_APIC_ID_MODIFIED inhibit reason to be
> cleared if/when all APICs in xAPIC mode set their APIC ID back to the
> expected vcpu_id value.
> 
> Fold the functionality previously in kvm_lapic_xapic_id_updated() into
> kvm_recalculate_apic_map(), as this allows examining all APICs in one
> pass.
> 
> Fixes: 3743c2f02517 ("KVM: x86: inhibit APICv/AVIC on changes to APIC ID or APIC base")
> Signed-off-by: Greg Edwards <gedwards@....com>
> ---

Reviewed-by: Sean Christopherson <seanjc@...gle.com>