[RFC PATCH v2 2/2] add support for Hyper-V invariant TSC

[Vadim Rozenfeld <vrozenfe@redhat.com>]

The following patch allows to activate a partition reference 
time enlightenment that is based on the host platform's support 
for an Invariant Time Stamp Counter (iTSC).
NOTE: This code will survive migration due to lack of VM stop/resume
handlers, when offset, scale and sequence should be
readjusted. 

---
 arch/x86/kvm/x86.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9645dab..b423fe4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1838,7 +1838,6 @@ static int set_msr_hyperv_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 		u64 gfn;
 		unsigned long addr;
 		HV_REFERENCE_TSC_PAGE tsc_ref;
-		tsc_ref.TscSequence = 0;
 		if (!(data & HV_X64_MSR_TSC_REFERENCE_ENABLE)) {
 			kvm->arch.hv_tsc_page = data;
 			break;
@@ -1848,6 +1847,11 @@ static int set_msr_hyperv_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 				HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT);
 		if (kvm_is_error_hva(addr))
 			return 1;
+		tsc_ref.TscSequence =
+				boot_cpu_has(X86_FEATURE_CONSTANT_TSC) ? 1 : 0;
+		tsc_ref.TscScale =
+				((10000LL << 32) / vcpu->arch.virtual_tsc_khz) << 32;
+		tsc_ref.TscOffset = 0;
 		if (__copy_to_user((void __user *)addr, &tsc_ref, sizeof(tsc_ref)))
 			return 1;
 		mark_page_dirty(kvm, gfn);
-- 
1.8.1.2