kvm: kvmclock: use get_cpu() and put_cpu()

We can use get_cpu() and put_cpu() to replace
preempt_disable()/cpu = smp_processor_id() and
preempt_enable() for slightly better code.
Signed-off-by: NTiejun Chen <tiejun.chen@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kernel/kvmclock.c

@@ -59,13 +59,12 @@ static void kvm_get_wallclock(struct timespec *now)
 
 	native_write_msr(msr_kvm_wall_clock, low, high);
 
-	preempt_disable();
-	cpu = smp_processor_id();
+	cpu = get_cpu();
 
 	vcpu_time = &hv_clock[cpu].pvti;
 	pvclock_read_wallclock(&wall_clock, vcpu_time, now);
 
-	preempt_enable();
+	put_cpu();
 }
 
 static int kvm_set_wallclock(const struct timespec *now)
@@ -107,11 +106,10 @@ static unsigned long kvm_get_tsc_khz(void)
 	int cpu;
 	unsigned long tsc_khz;
 
-	preempt_disable();
-	cpu = smp_processor_id();
+	cpu = get_cpu();
 	src = &hv_clock[cpu].pvti;
 	tsc_khz = pvclock_tsc_khz(src);
-	preempt_enable();
+	put_cpu();
 	return tsc_khz;
 }
 
@@ -284,23 +282,22 @@ int __init kvm_setup_vsyscall_timeinfo(void)
 
 	size = PAGE_ALIGN(sizeof(struct pvclock_vsyscall_time_info)*NR_CPUS);
 
-	preempt_disable();
-	cpu = smp_processor_id();
+	cpu = get_cpu();
 
 	vcpu_time = &hv_clock[cpu].pvti;
 	flags = pvclock_read_flags(vcpu_time);
 
 	if (!(flags & PVCLOCK_TSC_STABLE_BIT)) {
-		preempt_enable();
+		put_cpu();
 		return 1;
 	}
 
 	if ((ret = pvclock_init_vsyscall(hv_clock, size))) {
-		preempt_enable();
+		put_cpu();
 		return ret;
 	}
 
-	preempt_enable();
+	put_cpu();
 
 	kvm_clock.archdata.vclock_mode = VCLOCK_PVCLOCK;
 #endif