KVM: x86: Warn about unstable TSC

If creating an SMP guest with unstable host TSC, issue a warning

Signed-off-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 699c6b89c1b4..a8dee58e8716 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5457,6 +5457,10 @@ void kvm_arch_vcpu_free(struct kvm_vcpu *vcpu)
 struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
                                                 unsigned int id)
 {
+        if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0)
+                printk_once(KERN_WARNING
+                "kvm: SMP vm created on host with unstable TSC; "
+                "guest TSC will not be reliable\n");
         return kvm_x86_ops->vcpu_create(kvm, id);
 }