KVM: x86: Harden against cpufreq

If cpufreq can't determine the CPU khz, or cpufreq is not compiled in,
we should fallback to the measured TSC khz.

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

1 files changed, 12 insertions, 4 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 098e7f886306..3cffa2cac70b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1348,8 +1348,12 @@ out:
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
         kvm_x86_ops->vcpu_load(vcpu, cpu);
-        if (unlikely(per_cpu(cpu_tsc_khz, cpu) == 0))
-                per_cpu(cpu_tsc_khz, cpu) = cpufreq_quick_get(cpu);
+        if (unlikely(per_cpu(cpu_tsc_khz, cpu) == 0)) {
+                unsigned long khz = cpufreq_quick_get(cpu);
+                if (!khz)
+                        khz = tsc_khz;
+                per_cpu(cpu_tsc_khz, cpu) = khz;
+        }
         kvm_request_guest_time_update(vcpu);
 }
 
@@ -3144,8 +3148,12 @@ static void kvm_timer_init(void)
         if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
                 cpufreq_register_notifier(&kvmclock_cpufreq_notifier_block,
                                           CPUFREQ_TRANSITION_NOTIFIER);
-                for_each_online_cpu(cpu)
-                        per_cpu(cpu_tsc_khz, cpu) = cpufreq_get(cpu);
+                for_each_online_cpu(cpu) {
+                        unsigned long khz = cpufreq_get(cpu);
+                        if (!khz)
+                                khz = tsc_khz;
+                        per_cpu(cpu_tsc_khz, cpu) = khz;
+                }
         } else {
                 for_each_possible_cpu(cpu)
                         per_cpu(cpu_tsc_khz, cpu) = tsc_khz;