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SubjectRe: [PATCH 19/19] Revert "KVM: SVM: Do not throw warning when calling avic_vcpu_load on a running vcpu"
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On Wed, 2022-08-31 at 00:35 +0000, Sean Christopherson wrote:
> Turns out that some warnings exist for good reasons. Restore the warning
> in avic_vcpu_load() that guards against calling avic_vcpu_load() on a
> running vCPU now that KVM avoids doing so when switching between x2APIC
> and xAPIC. The entire point of the WARN is to highlight that KVM should
> not be reloading an AVIC.
>
> Opportunistically convert the WARN_ON() to WARN_ON_ONCE() to avoid
> spamming the kernel if it does fire.
>
> This reverts commit c0caeee65af3944b7b8abbf566e7cc1fae15c775.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/svm/avic.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index b2033a56010c..3c300113d40b 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -1080,6 +1080,7 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> return;
>
> entry = READ_ONCE(*(svm->avic_physical_id_cache));
> + WARN_ON_ONCE(entry & AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK);
>
> entry &= ~AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK;
> entry |= (h_physical_id & AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK);

Note that this warning was removed because it would trigger wheh x2avic code would switch
between xapic and x2apic.

I do agree 100% that this warning is useful.

Best regards,
Maxim Levitsky

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