From: David Woodhouse dwmw@amazon.co.uk
KVM does make an attempt to cope with non-constant TSC, and has notifiers to handle host TSC frequency changes. However, it *only* adjusts the KVM clock, and doesn't adjust TSC frequency scaling when the host changes.
This is presumably because non-constant TSCs were fixed in hardware long before TSC scaling was implemented, so there should never be real CPUs which have TSC scaling but *not* CONSTANT_TSC.
Such a combination could potentially happen in some odd L1 nesting environment, but it isn't worth trying to support it. Just make the dependency explicit.
Signed-off-by: David Woodhouse dwmw@amazon.co.uk Reviewed-by: Paul Durrant paul@xen.org --- arch/x86/kvm/svm/svm.c | 3 ++- arch/x86/kvm/vmx/vmx.c | 2 +- 2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 0f3b59da0d4a..4d3ec1c3231e 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -5202,7 +5202,8 @@ static __init int svm_hardware_setup(void) kvm_enable_efer_bits(EFER_FFXSR);
if (tsc_scaling) { - if (!boot_cpu_has(X86_FEATURE_TSCRATEMSR)) { + if (!boot_cpu_has(X86_FEATURE_TSCRATEMSR) || + !boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) { tsc_scaling = false; } else { pr_info("TSC scaling supported\n"); diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 6780313914f8..bee830adf744 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -8428,7 +8428,7 @@ __init int vmx_hardware_setup(void) if (!enable_apicv || !cpu_has_vmx_ipiv()) enable_ipiv = false;
- if (cpu_has_vmx_tsc_scaling()) + if (cpu_has_vmx_tsc_scaling() && boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) kvm_caps.has_tsc_control = true;
kvm_caps.max_tsc_scaling_ratio = KVM_VMX_TSC_MULTIPLIER_MAX;