KVM: x86: Convert TSC writes to TSC offset writes

Change svm / vmx to be the same internally and write TSC offset
instead of bare TSC in helper functions.  Isolated as a single
patch to contain code movement.

Signed-off-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/svm.c

@@ -701,6 +701,20 @@ static void init_sys_seg(struct vmcb_seg *seg, uint32_t type)
 	seg->base = 0;
 }
 
+static void svm_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+	u64 g_tsc_offset = 0;
+
+	if (is_nested(svm)) {
+		g_tsc_offset = svm->vmcb->control.tsc_offset -
+			       svm->nested.hsave->control.tsc_offset;
+		svm->nested.hsave->control.tsc_offset = offset;
+	}
+
+	svm->vmcb->control.tsc_offset = offset + g_tsc_offset;
+}
+
 static void init_vmcb(struct vcpu_svm *svm)
 {
 	struct vmcb_control_area *control = &svm->vmcb->control;
@@ -901,7 +915,7 @@ static struct kvm_vcpu *svm_create_vcpu(struct kvm *kvm, unsigned int id)
 	svm->vmcb_pa = page_to_pfn(page) << PAGE_SHIFT;
 	svm->asid_generation = 0;
 	init_vmcb(svm);
-	svm->vmcb->control.tsc_offset = 0-native_read_tsc();
+	svm_write_tsc_offset(&svm->vcpu, 0-native_read_tsc());
 
 	err = fx_init(&svm->vcpu);
 	if (err)
@@ -2566,20 +2580,9 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, unsigned ecx, u64 data)
 	struct vcpu_svm *svm = to_svm(vcpu);
 
 	switch (ecx) {
-	case MSR_IA32_TSC: {
-		u64 tsc_offset = data - native_read_tsc();
-		u64 g_tsc_offset = 0;
-
-		if (is_nested(svm)) {
-			g_tsc_offset = svm->vmcb->control.tsc_offset -
-				       svm->nested.hsave->control.tsc_offset;
-			svm->nested.hsave->control.tsc_offset = tsc_offset;
-		}
-
-		svm->vmcb->control.tsc_offset = tsc_offset + g_tsc_offset;
-
+	case MSR_IA32_TSC:
+		svm_write_tsc_offset(vcpu, data - native_read_tsc());
 		break;
-	}
 	case MSR_STAR:
 		svm->vmcb->save.star = data;
 		break;

arch/x86/kvm/vmx.c

@@ -1149,9 +1149,9 @@ static u64 guest_read_tsc(void)
  * writes 'guest_tsc' into guest's timestamp counter "register"
  * guest_tsc = host_tsc + tsc_offset ==> tsc_offset = guest_tsc - host_tsc
  */
-static void guest_write_tsc(u64 guest_tsc, u64 host_tsc)
+static void vmx_write_tsc_offset(u64 offset)
 {
-	vmcs_write64(TSC_OFFSET, guest_tsc - host_tsc);
+	vmcs_write64(TSC_OFFSET, offset);
 }
 
 /*
@@ -1255,7 +1255,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
 		break;
 	case MSR_IA32_TSC:
 		rdtscll(host_tsc);
-		guest_write_tsc(data, host_tsc);
+		vmx_write_tsc_offset(data - host_tsc);
 		break;
 	case MSR_IA32_CR_PAT:
 		if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT) {
@@ -2512,7 +2512,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
 {
 	u32 host_sysenter_cs, msr_low, msr_high;
 	u32 junk;
-	u64 host_pat, tsc_this;
+	u64 host_pat;
 	unsigned long a;
 	struct desc_ptr dt;
 	int i;
@@ -2653,8 +2653,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
 		vmx->vcpu.arch.cr4_guest_owned_bits |= X86_CR4_PGE;
 	vmcs_writel(CR4_GUEST_HOST_MASK, ~vmx->vcpu.arch.cr4_guest_owned_bits);
 
-	tsc_this = native_read_tsc();
-	guest_write_tsc(0, tsc_this);
+	vmx_write_tsc_offset(0-native_read_tsc());
 
 	return 0;
 }