1 files changed, 41 insertions, 5 deletions

diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index b3c13cb898..6adbff3d74 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -740,26 +740,62 @@ static bool hyperv_enabled(X86CPU *cpu)
          cpu->hyperv_features || cpu->hyperv_passthrough);
 }
 
+/*
+ * Check whether target_freq is within conservative
+ * ntp correctable bounds (250ppm) of freq
+ */
+static inline bool freq_within_bounds(int freq, int target_freq)
+{
+        int max_freq = freq + (freq * 250 / 1000000);
+        int min_freq = freq - (freq * 250 / 1000000);
+
+        if (target_freq >= min_freq && target_freq <= max_freq) {
+                return true;
+        }
+
+        return false;
+}
+
 static int kvm_arch_set_tsc_khz(CPUState *cs)
 {
     X86CPU *cpu = X86_CPU(cs);
     CPUX86State *env = &cpu->env;
-    int r;
+    int r, cur_freq;
+    bool set_ioctl = false;
 
     if (!env->tsc_khz) {
         return 0;
     }
 
-    r = kvm_check_extension(cs->kvm_state, KVM_CAP_TSC_CONTROL) ?
+    cur_freq = kvm_check_extension(cs->kvm_state, KVM_CAP_GET_TSC_KHZ) ?
+               kvm_vcpu_ioctl(cs, KVM_GET_TSC_KHZ) : -ENOTSUP;
+
+    /*
+     * If TSC scaling is supported, attempt to set TSC frequency.
+     */
+    if (kvm_check_extension(cs->kvm_state, KVM_CAP_TSC_CONTROL)) {
+        set_ioctl = true;
+    }
+
+    /*
+     * If desired TSC frequency is within bounds of NTP correction,
+     * attempt to set TSC frequency.
+     */
+    if (cur_freq != -ENOTSUP && freq_within_bounds(cur_freq, env->tsc_khz)) {
+        set_ioctl = true;
+    }
+
+    r = set_ioctl ?
         kvm_vcpu_ioctl(cs, KVM_SET_TSC_KHZ, env->tsc_khz) :
         -ENOTSUP;
+
     if (r < 0) {
         /* When KVM_SET_TSC_KHZ fails, it's an error only if the current
          * TSC frequency doesn't match the one we want.
          */
-        int cur_freq = kvm_check_extension(cs->kvm_state, KVM_CAP_GET_TSC_KHZ) ?
-                       kvm_vcpu_ioctl(cs, KVM_GET_TSC_KHZ) :
-                       -ENOTSUP;
+        cur_freq = kvm_check_extension(cs->kvm_state, KVM_CAP_GET_TSC_KHZ) ?
+                   kvm_vcpu_ioctl(cs, KVM_GET_TSC_KHZ) :
+                   -ENOTSUP;
         if (cur_freq <= 0 || cur_freq != env->tsc_khz) {
             warn_report("TSC frequency mismatch between "
                         "VM (%" PRId64 " kHz) and host (%d kHz), "