Re: [PATCH 07/15] KVM: Use dedicated flag to track if KVM is handling an NMI from guest
From: Sean Christopherson <seanjc@google.com>
Date: 2021-08-27 14:58:43
Also in:
kvmarm, linux-arm-kernel, linux-perf-users, linux-riscv, lkml, xen-devel
On Fri, Aug 27, 2021, Peter Zijlstra wrote:
On Thu, Aug 26, 2021 at 05:57:10PM -0700, Sean Christopherson wrote:quoted
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index 5cedc0e8a5d5..4c5ba4128b38 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h@@ -395,9 +395,10 @@ static inline void kvm_unregister_perf_callbacks(void) DECLARE_PER_CPU(struct kvm_vcpu *, current_vcpu); -static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu) +static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu, bool is_nmi) { __this_cpu_write(current_vcpu, vcpu); + WRITE_ONCE(vcpu->arch.handling_nmi_from_guest, is_nmi); kvm_register_perf_callbacks(); }@@ -406,6 +407,7 @@ static inline void kvm_after_interrupt(struct kvm_vcpu *vcpu) { kvm_unregister_perf_callbacks(); + WRITE_ONCE(vcpu->arch.handling_nmi_from_guest, false); __this_cpu_write(current_vcpu, NULL); }Does this rely on kvm_{,un}register_perf_callback() being a function call and thus implying a sequence point to order the stores?
No, I'm just terrible at remembering which macros provide what ordering guarantees, i.e. I was thinking WRITE_ONCE provided guarantees against compiler reordering.