Commit f6e16d5a authored by Gerd Hoffmann's avatar Gerd Hoffmann Committed by Avi Kivity
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x86: KVM guest: Use the paravirt clocksource structs and functions

This patch updates the kvm host code to use the pvclock structs
and functions, thereby making it compatible with Xen.

The patch also fixes an initialization bug: on SMP systems the
per-cpu has two different locations early at boot and after CPU
bringup.  kvmclock must take that in account when registering the
physical address within the host.
Signed-off-by: default avatarGerd Hoffmann <>
Signed-off-by: default avatarAvi Kivity <>
parent 50d0a0f9
......@@ -383,6 +383,7 @@ config VMI
config KVM_CLOCK
bool "KVM paravirtualized clock"
depends on !(X86_VISWS || X86_VOYAGER)
Turning on this option will allow you to run a paravirtualized clock
......@@ -18,6 +18,7 @@
#include <linux/clocksource.h>
#include <linux/kvm_para.h>
#include <asm/pvclock.h>
#include <asm/arch_hooks.h>
#include <asm/msr.h>
#include <asm/apic.h>
......@@ -36,18 +37,9 @@ static int parse_no_kvmclock(char *arg)
early_param("no-kvmclock", parse_no_kvmclock);
/* The hypervisor will put information about time periodically here */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct kvm_vcpu_time_info, hv_clock);
#define get_clock(cpu, field) per_cpu(hv_clock, cpu).field
static DEFINE_PER_CPU_SHARED_ALIGNED(struct pvclock_vcpu_time_info, hv_clock);
static struct pvclock_wall_clock wall_clock;
static inline u64 kvm_get_delta(u64 last_tsc)
int cpu = smp_processor_id();
u64 delta = native_read_tsc() - last_tsc;
return (delta * get_clock(cpu, tsc_to_system_mul)) >> KVM_SCALE;
static struct kvm_wall_clock wall_clock;
static cycle_t kvm_clock_read(void);
* The wallclock is the time of day when we booted. Since then, some time may
* have elapsed since the hypervisor wrote the data. So we try to account for
......@@ -55,64 +47,37 @@ static cycle_t kvm_clock_read(void);
static unsigned long kvm_get_wallclock(void)
u32 wc_sec, wc_nsec;
u64 delta;
struct pvclock_vcpu_time_info *vcpu_time;
struct timespec ts;
int version, nsec;
int low, high;
low = (int)__pa(&wall_clock);
high = ((u64)__pa(&wall_clock) >> 32);
native_write_msr(MSR_KVM_WALL_CLOCK, low, high);
delta = kvm_clock_read();
vcpu_time = &get_cpu_var(hv_clock);
pvclock_read_wallclock(&wall_clock, vcpu_time, &ts);
native_write_msr(MSR_KVM_WALL_CLOCK, low, high);
do {
version = wall_clock.wc_version;
wc_sec = wall_clock.wc_sec;
wc_nsec = wall_clock.wc_nsec;
} while ((wall_clock.wc_version != version) || (version & 1));
delta = kvm_clock_read() - delta;
delta += wc_nsec;
nsec = do_div(delta, NSEC_PER_SEC);
set_normalized_timespec(&ts, wc_sec + delta, nsec);
* Of all mechanisms of time adjustment I've tested, this one
* was the champion!
return ts.tv_sec + 1;
return ts.tv_sec;
static int kvm_set_wallclock(unsigned long now)
return 0;
return -1;
* This is our read_clock function. The host puts an tsc timestamp each time
* it updates a new time. Without the tsc adjustment, we can have a situation
* in which a vcpu starts to run earlier (smaller system_time), but probes
* time later (compared to another vcpu), leading to backwards time
static cycle_t kvm_clock_read(void)
u64 last_tsc, now;
int cpu;
struct pvclock_vcpu_time_info *src;
cycle_t ret;
cpu = smp_processor_id();
last_tsc = get_clock(cpu, tsc_timestamp);
now = get_clock(cpu, system_time);
now += kvm_get_delta(last_tsc);
return now;
src = &get_cpu_var(hv_clock);
ret = pvclock_clocksource_read(src);
return ret;
static struct clocksource kvm_clock = {
.name = "kvm-clock",
.read = kvm_clock_read,
......@@ -123,13 +88,14 @@ static struct clocksource kvm_clock = {
static int kvm_register_clock(void)
static int kvm_register_clock(char *txt)
int cpu = smp_processor_id();
int low, high;
low = (int)__pa(&per_cpu(hv_clock, cpu)) | 1;
high = ((u64)__pa(&per_cpu(hv_clock, cpu)) >> 32);
printk(KERN_INFO "kvm-clock: cpu %d, msr %x:%x, %s\n",
cpu, high, low, txt);
return native_write_msr_safe(MSR_KVM_SYSTEM_TIME, low, high);
......@@ -140,12 +106,20 @@ static void kvm_setup_secondary_clock(void)
* Now that the first cpu already had this clocksource initialized,
* we shouldn't fail.
WARN_ON(kvm_register_clock("secondary cpu clock"));
/* ok, done with our trickery, call native */
void __init kvm_smp_prepare_boot_cpu(void)
WARN_ON(kvm_register_clock("primary cpu clock"));
* After the clock is registered, the host will keep writing to the
* registered memory location. If the guest happens to shutdown, this memory
......@@ -174,13 +148,16 @@ void __init kvmclock_init(void)
if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)) {
if (kvm_register_clock())
if (kvm_register_clock("boot clock"))
pv_time_ops.get_wallclock = kvm_get_wallclock;
pv_time_ops.set_wallclock = kvm_set_wallclock;
pv_time_ops.sched_clock = kvm_clock_read;
pv_apic_ops.setup_secondary_clock = kvm_setup_secondary_clock;
smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
machine_ops.shutdown = kvm_shutdown;
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