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>
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 4fbab24..d9bec5e 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1149,9 +1149,9 @@
  * 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 @@
 		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 @@
 {
 	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 @@
 		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;
 }