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Peter Anvin" , Andy Lutomirski , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Paolo Bonzini , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, loongarch@lists.linux.dev, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Kan Liang , Yongwei Ma , Mingwei Zhang , Xiong Zhang , Sandipan Das , Dapeng Mi Content-Type: text/plain; charset="us-ascii" On Fri, Aug 15, 2025, Peter Zijlstra wrote: > On Wed, Aug 06, 2025 at 12:56:31PM -0700, Sean Christopherson wrote: > > > @@ -2727,6 +2739,21 @@ static struct pmu pmu = { > > .filter = x86_pmu_filter, > > }; > > > > +void arch_perf_load_guest_context(unsigned long data) > > +{ > > + u32 masked = data & APIC_LVT_MASKED; > > + > > + apic_write(APIC_LVTPC, > > + APIC_DM_FIXED | PERF_GUEST_MEDIATED_PMI_VECTOR | masked); > > + this_cpu_write(x86_guest_ctx_loaded, true); > > +} > > I'm further confused, why would this ever be masked? The idea is to match the guest's LVTPC state so that KVM doesn't trigger IRQ VM-Exits on counter overflow when the guest's LVTPC is masked.