The Linux TSC calibration procedure is subject to small variations
(its common to see +-1 kHz difference between reboots on a given CPU, for example).
So migrating a guest between two hosts with identical processor can fail, in case
of a small variation in calibrated TSC between them.
Allow a conservative 250ppm error between host TSC and VM TSC frequencies,
rather than requiring an exact match. NTP daemon in the guest can
correct this difference.
Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3156e25..39a6664 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1772,6 +1772,8 @@ static int set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz, bool scale)
/* TSC scaling supported? */
if (!kvm_has_tsc_control) {
+ if (!scale)
+ return 0;
if (user_tsc_khz > tsc_khz) {
vcpu->arch.tsc_catchup = 1;
vcpu->arch.tsc_always_catchup = 1;
@@ -4473,7 +4475,8 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
r = -EINVAL;
user_tsc_khz = (u32)arg;
- if (user_tsc_khz >= kvm_max_guest_tsc_khz)
+ if (kvm_has_tsc_control &&
+ user_tsc_khz >= kvm_max_guest_tsc_khz)
goto out;
if (user_tsc_khz == 0)
