Commit bd3d1ec3 authored Feb 03, 2011 by Avi Kivity Committed by Marcelo Tosatti Mar 17, 2011

KVM: SVM: check for progress after IRET interception

When we enable an NMI window, we ask for an IRET intercept, since
the IRET re-enables NMIs. However, the IRET intercept happens before
the instruction executes, while the NMI window architecturally opens
afterwards.

To compensate for this mismatch, we only open the NMI window in the
following exit, assuming that the IRET has by then executed; however,
this assumption is not always correct; we may exit due to a host interrupt
or page fault, without having executed the instruction.

Fix by checking for forward progress by recording and comparing the IRET's
rip. This is somewhat of a hack, since an unchaging rip does not mean that
no forward progress has been made, but is the simplest fix for now.

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

parent f8636849

arch/x86/kvm/svm.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -135,6 +135,8 @@ struct vcpu_svm {

		u32 *msrpm;

		ulong nmi_iret_rip;

		struct nested_state nested;

		bool nmi_singlestep;
		@@ -2653,6 +2655,7 @@ static int iret_interception(struct vcpu_svm *svm)
		++svm->vcpu.stat.nmi_window_exits;
		clr_intercept(svm, INTERCEPT_IRET);
		svm->vcpu.arch.hflags \|= HF_IRET_MASK;
		svm->nmi_iret_rip = kvm_rip_read(&svm->vcpu);
		return 1;
		}

		@@ -3474,7 +3477,12 @@ static void svm_complete_interrupts(struct vcpu_svm *svm)

		svm->int3_injected = 0;

		if (svm->vcpu.arch.hflags & HF_IRET_MASK) {
		/*
		* If we've made progress since setting HF_IRET_MASK, we've
		* executed an IRET and can allow NMI injection.
		*/
		if ((svm->vcpu.arch.hflags & HF_IRET_MASK)
		&& kvm_rip_read(&svm->vcpu) != svm->nmi_iret_rip) {
		svm->vcpu.arch.hflags &= ~(HF_NMI_MASK \| HF_IRET_MASK);
		kvm_make_request(KVM_REQ_EVENT, &svm->vcpu);
		}

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