[v3,11/16] KVM: x86: More precisely identify NMI from guest when handling PMI

Commit Message

Sean Christopherson Sept. 22, 2021, 12:05 a.m. UTC

Differntiate between IRQ and NMI for KVM's PMC overflow callback, which
was originally invoked in response to an NMI that arrived while the guest
was running, but was inadvertantly changed to fire on IRQs as well when
support for perf without PMU/NMI was added to KVM.  In practice, this
should be a nop as the PMC overflow callback shouldn't be reached, but
it's a cheap and easy fix that also better documents the situation.

Note, this also doesn't completely prevent false positives if perf
somehow ends up calling into KVM, e.g. an NMI can arrive in host after
KVM sets its flag.

Fixes: dd60d217062f ("KVM: x86: Fix perf timer mode IP reporting")
Signed-off-by: Sean Christopherson <[e-mail]>
---
 arch/x86/kvm/svm/svm.c |  2 +-
 arch/x86/kvm/vmx/vmx.c |  4 +++-
 arch/x86/kvm/x86.c     |  2 +-
 arch/x86/kvm/x86.h     | 13 ++++++++++---
 4 files changed, 15 insertions(+), 6 deletions(-)

Comments

Paolo Bonzini Sept. 22, 2021, 6:38 a.m. UTC | #1

On 22/09/21 02:05, Sean Christopherson wrote:
> Note, this also doesn't completely prevent false positives if perf
> somehow ends up calling into KVM, e.g. an NMI can arrive in host after
> KVM sets its flag.

s/calling into KVM/being called from KVM/ ?

Not sure about what you meant though.  The code is nice, so

Reviewed-by: Paolo Bonzini <[e-mail]>

Paolo

Patch

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 1a70e11f0487..0a0c01744b63 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3843,7 +3843,7 @@  static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
 	}
 
 	if (unlikely(svm->vmcb->control.exit_code == SVM_EXIT_NMI))
-		kvm_before_interrupt(vcpu);
+		kvm_before_interrupt(vcpu, KVM_HANDLING_NMI);
 
 	kvm_load_host_xsave_state(vcpu);
 	stgi();
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f19d72136f77..61a4f5ff2acd 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6344,7 +6344,9 @@  void vmx_do_interrupt_nmi_irqoff(unsigned long entry);
 static void handle_interrupt_nmi_irqoff(struct kvm_vcpu *vcpu,
 					unsigned long entry)
 {
-	kvm_before_interrupt(vcpu);
+	bool is_nmi = entry == (unsigned long)asm_exc_nmi_noist;
+
+	kvm_before_interrupt(vcpu, is_nmi ? KVM_HANDLING_NMI : KVM_HANDLING_IRQ);
 	vmx_do_interrupt_nmi_irqoff(entry);
 	kvm_after_interrupt(vcpu);
 }
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 24a6faa07442..412646b973bb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9676,7 +9676,7 @@  static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 	 * interrupts on processors that implement an interrupt shadow, the
 	 * stat.exits increment will do nicely.
 	 */
-	kvm_before_interrupt(vcpu);
+	kvm_before_interrupt(vcpu, KVM_HANDLING_IRQ);
 	local_irq_enable();
 	++vcpu->stat.exits;
 	local_irq_disable();
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index a9c107e7c907..9b26f9b09d2a 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -387,9 +387,16 @@  static inline bool kvm_cstate_in_guest(struct kvm *kvm)
 	return kvm->arch.cstate_in_guest;
 }
 
-static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu)
+enum kvm_intr_type {
+	/* Values are arbitrary, but must be non-zero. */
+	KVM_HANDLING_IRQ = 1,
+	KVM_HANDLING_NMI,
+};
+
+static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu,
+					enum kvm_intr_type intr)
 {
-	WRITE_ONCE(vcpu->arch.handling_intr_from_guest, 1);
+	WRITE_ONCE(vcpu->arch.handling_intr_from_guest, (u8)intr);
 }
 
 static inline void kvm_after_interrupt(struct kvm_vcpu *vcpu)
@@ -399,7 +406,7 @@  static inline void kvm_after_interrupt(struct kvm_vcpu *vcpu)
 
 static inline bool kvm_handling_nmi_from_guest(struct kvm_vcpu *vcpu)
 {
-	return !!vcpu->arch.handling_intr_from_guest;
+	return vcpu->arch.handling_intr_from_guest == KVM_HANDLING_NMI;
 }
 
 static inline bool kvm_pat_valid(u64 data)