Commit f8636849 authored Feb 03, 2011 by Avi Kivity Committed by Marcelo Tosatti Mar 17, 2011

KVM: Fix race between nmi injection and enabling nmi window



The interrupt injection logic looks something like

  if an nmi is pending, and nmi injection allowed
    inject nmi
  if an nmi is pending
    request exit on nmi window

the problem is that "nmi is pending" can be set asynchronously by
the PIT; if it happens to fire between the two if statements, we
will request an nmi window even though nmi injection is allowed.  On
SVM, this has disasterous results, since it causes eflags.TF to be
set in random guest code.

The fix is simple; make nmi_pending synchronous using the standard
vcpu->requests mechanism; this ensures the code above is completely
synchronous wrt nmi_pending.

Signed-off-by: Avi Kivity <avi@redhat.com>

parent 217ece61

arch/x86/kvm/x86.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -360,8 +360,8 @@ void kvm_propagate_fault(struct kvm_vcpu vcpu, struct x86_exception fault)

		void kvm_inject_nmi(struct kvm_vcpu *vcpu)
		{
		kvm_make_request(KVM_REQ_NMI, vcpu);
		kvm_make_request(KVM_REQ_EVENT, vcpu);
		vcpu->arch.nmi_pending = 1;
		}
		EXPORT_SYMBOL_GPL(kvm_inject_nmi);

		@@ -5180,6 +5180,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
		r = 1;
		goto out;
		}
		if (kvm_check_request(KVM_REQ_NMI, vcpu))
		vcpu->arch.nmi_pending = true;
		}

		r = kvm_mmu_reload(vcpu);

include/linux/kvm_host.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -43,6 +43,7 @@
		#define KVM_REQ_DEACTIVATE_FPU 10
		#define KVM_REQ_EVENT 11
		#define KVM_REQ_APF_HALT 12
		#define KVM_REQ_NMI 13

		#define KVM_USERSPACE_IRQ_SOURCE_ID 0

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