kvm: x86: emulate monitor and mwait instructions as nop
Treat monitor and mwait instructions as nop, which is architecturally
correct (but inefficient) behavior. We do this to prevent misbehaving
guests (e.g. OS X <= 10.7) from crashing after they fail to check for
monitor/mwait availability via cpuid.
Since mwait-based idle loops relying on these nop-emulated instructions
would keep the host CPU pegged at 100%, do NOT advertise their presence
via cpuid, to prevent compliant guests from using them inadvertently.
Signed-off-by: Gabriel L. Somlo <somlo@cmu.edu>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 7f4f9c2..0b7d58d 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2770,12 +2770,6 @@
return 1;
}
-static int invalid_op_interception(struct vcpu_svm *svm)
-{
- kvm_queue_exception(&svm->vcpu, UD_VECTOR);
- return 1;
-}
-
static int task_switch_interception(struct vcpu_svm *svm)
{
u16 tss_selector;
@@ -3287,6 +3281,24 @@
return 1;
}
+static int nop_interception(struct vcpu_svm *svm)
+{
+ skip_emulated_instruction(&(svm->vcpu));
+ return 1;
+}
+
+static int monitor_interception(struct vcpu_svm *svm)
+{
+ printk_once(KERN_WARNING "kvm: MONITOR instruction emulated as NOP!\n");
+ return nop_interception(svm);
+}
+
+static int mwait_interception(struct vcpu_svm *svm)
+{
+ printk_once(KERN_WARNING "kvm: MWAIT instruction emulated as NOP!\n");
+ return nop_interception(svm);
+}
+
static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
[SVM_EXIT_READ_CR0] = cr_interception,
[SVM_EXIT_READ_CR3] = cr_interception,
@@ -3344,8 +3356,8 @@
[SVM_EXIT_CLGI] = clgi_interception,
[SVM_EXIT_SKINIT] = skinit_interception,
[SVM_EXIT_WBINVD] = emulate_on_interception,
- [SVM_EXIT_MONITOR] = invalid_op_interception,
- [SVM_EXIT_MWAIT] = invalid_op_interception,
+ [SVM_EXIT_MONITOR] = monitor_interception,
+ [SVM_EXIT_MWAIT] = mwait_interception,
[SVM_EXIT_XSETBV] = xsetbv_interception,
[SVM_EXIT_NPF] = pf_interception,
};