KVM: x86: Explicitly disable TSC scaling without CONSTANT_TSC

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>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 0f3b59da0d4a891431b9474c575552a133407026..4d3ec1c3231e3465b7f6d34fc8a7c5cd9cbe2cc7 100644 (file)
--- 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 6780313914f86cef1cfad93f860afdd854632aee..bee830adf744436856f61804d62a73221bb85a55 100644 (file)
--- 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;