On Fri, Sep 01, 2023, Jim Mattson wrote:
> Per the SDM, "When the local APIC handles a performance-monitoring
> counters interrupt, it automatically sets the mask flag in the LVT
> performance counter register."
>
> Add this behavior to KVM's local APIC emulation, to reduce the
> incidence of "dazed and confused" spurious NMI warnings in Linux
> guests (at least, those that use a PMI handler with "late_ack").
>
> Fixes: 23930f9521c9 ("KVM: x86: Enable NMI Watchdog via in-kernel PIT source")
> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
Tested-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
I see consistent number of PMIs and NMIs when running perf on an idle
VM.
> ---
> arch/x86/kvm/lapic.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index a983a16163b1..1a79ec54ae1e 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2743,6 +2743,8 @@ int kvm_apic_local_deliver(struct kvm_lapic *apic, int lvt_type)
> vector = reg & APIC_VECTOR_MASK;
> mode = reg & APIC_MODE_MASK;
> trig_mode = reg & APIC_LVT_LEVEL_TRIGGER;
> + if (lvt_type == APIC_LVTPC)
> + kvm_lapic_set_reg(apic, lvt_type, reg | APIC_LVT_MASKED);
> return __apic_accept_irq(apic, mode, vector, 1, trig_mode,
> NULL);
> }
> --
> 2.42.0.283.g2d96d420d3-goog
>
