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qemu-e2k/hw/i386/kvm/clock.c

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/*
* QEMU KVM support, paravirtual clock device
*
* Copyright (C) 2011 Siemens AG
*
* Authors:
* Jan Kiszka <jan.kiszka@siemens.com>
*
* This work is licensed under the terms of the GNU GPL version 2.
* See the COPYING file in the top-level directory.
*
* Contributions after 2012-01-13 are licensed under the terms of the
* GNU GPL, version 2 or (at your option) any later version.
*/
#include "qemu/osdep.h"
#include "qemu-common.h"
#include "cpu.h"
#include "qemu/host-utils.h"
#include "sysemu/sysemu.h"
#include "sysemu/kvm.h"
#include "sysemu/hw_accel.h"
#include "kvm_i386.h"
#include "hw/sysbus.h"
#include "hw/kvm/clock.h"
#include "qapi/error.h"
#include <linux/kvm.h>
#include <linux/kvm_para.h>
#define TYPE_KVM_CLOCK "kvmclock"
#define KVM_CLOCK(obj) OBJECT_CHECK(KVMClockState, (obj), TYPE_KVM_CLOCK)
typedef struct KVMClockState {
/*< private >*/
SysBusDevice busdev;
/*< public >*/
uint64_t clock;
bool clock_valid;
/* whether machine type supports reliable KVM_GET_CLOCK */
bool mach_use_reliable_get_clock;
/* whether the 'clock' value was obtained in a host with
* reliable KVM_GET_CLOCK */
bool clock_is_reliable;
} KVMClockState;
struct pvclock_vcpu_time_info {
uint32_t version;
uint32_t pad0;
uint64_t tsc_timestamp;
uint64_t system_time;
uint32_t tsc_to_system_mul;
int8_t tsc_shift;
uint8_t flags;
uint8_t pad[2];
} __attribute__((__packed__)); /* 32 bytes */
static uint64_t kvmclock_current_nsec(KVMClockState *s)
{
CPUState *cpu = first_cpu;
CPUX86State *env = cpu->env_ptr;
hwaddr kvmclock_struct_pa = env->system_time_msr & ~1ULL;
uint64_t migration_tsc = env->tsc;
struct pvclock_vcpu_time_info time;
uint64_t delta;
uint64_t nsec_lo;
uint64_t nsec_hi;
uint64_t nsec;
cpu_synchronize_state(cpu);
if (!(env->system_time_msr & 1ULL)) {
/* KVM clock not active */
return 0;
}
cpu_physical_memory_read(kvmclock_struct_pa, &time, sizeof(time));
assert(time.tsc_timestamp <= migration_tsc);
delta = migration_tsc - time.tsc_timestamp;
if (time.tsc_shift < 0) {
delta >>= -time.tsc_shift;
} else {
delta <<= time.tsc_shift;
}
mulu64(&nsec_lo, &nsec_hi, delta, time.tsc_to_system_mul);
nsec = (nsec_lo >> 32) | (nsec_hi << 32);
return nsec + time.system_time;
}
static void kvm_update_clock(KVMClockState *s)
{
struct kvm_clock_data data;
int ret;
ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
if (ret < 0) {
fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret));
abort();
}
s->clock = data.clock;
/* If kvm_has_adjust_clock_stable() is false, KVM_GET_CLOCK returns
* essentially CLOCK_MONOTONIC plus a guest-specific adjustment. This
* can drift from the TSC-based value that is computed by the guest,
* so we need to go through kvmclock_current_nsec(). If
* kvm_has_adjust_clock_stable() is true, and the flags contain
* KVM_CLOCK_TSC_STABLE, then KVM_GET_CLOCK returns a TSC-based value
* and kvmclock_current_nsec() is not necessary.
*
* Here, however, we need not check KVM_CLOCK_TSC_STABLE. This is because:
*
* - if the host has disabled the kvmclock master clock, the guest already
* has protection against time going backwards. This "safety net" is only
* absent when kvmclock is stable;
*
* - therefore, we can replace a check like
*
* if last KVM_GET_CLOCK was not reliable then
* read from memory
*
* with
*
* if last KVM_GET_CLOCK was not reliable && masterclock is enabled
* read from memory
*
* However:
*
* - if kvm_has_adjust_clock_stable() returns false, the left side is
* always true (KVM_GET_CLOCK is never reliable), and the right side is
* unknown (because we don't have data.flags). We must assume it's true
* and read from memory.
*
* - if kvm_has_adjust_clock_stable() returns true, the result of the &&
* is always false (masterclock is enabled iff KVM_GET_CLOCK is reliable)
*
* So we can just use this instead:
*
* if !kvm_has_adjust_clock_stable() then
* read from memory
*/
s->clock_is_reliable = kvm_has_adjust_clock_stable();
}
static void kvmclock_vm_state_change(void *opaque, int running,
RunState state)
{
KVMClockState *s = opaque;
CPUState *cpu;
int cap_clock_ctrl = kvm_check_extension(kvm_state, KVM_CAP_KVMCLOCK_CTRL);
int ret;
if (running) {
struct kvm_clock_data data = {};
/*
* If the host where s->clock was read did not support reliable
* KVM_GET_CLOCK, read kvmclock value from memory.
*/
if (!s->clock_is_reliable) {
uint64_t pvclock_via_mem = kvmclock_current_nsec(s);
/* We can't rely on the saved clock value, just discard it */
if (pvclock_via_mem) {
s->clock = pvclock_via_mem;
}
}
s->clock_valid = false;
data.clock = s->clock;
ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);
if (ret < 0) {
fprintf(stderr, "KVM_SET_CLOCK failed: %s\n", strerror(ret));
abort();
}
if (!cap_clock_ctrl) {
return;
}
CPU_FOREACH(cpu) {
ret = kvm_vcpu_ioctl(cpu, KVM_KVMCLOCK_CTRL, 0);
if (ret) {
if (ret != -EINVAL) {
fprintf(stderr, "%s: %s\n", __func__, strerror(-ret));
}
return;
}
}
} else {
if (s->clock_valid) {
return;
}
kvm_synchronize_all_tsc();
kvm_update_clock(s);
/*
* If the VM is stopped, declare the clock state valid to
* avoid re-reading it on next vmsave (which would return
* a different value). Will be reset when the VM is continued.
*/
s->clock_valid = true;
}
}
static void kvmclock_realize(DeviceState *dev, Error **errp)
{
KVMClockState *s = KVM_CLOCK(dev);
if (!kvm_enabled()) {
error_setg(errp, "kvmclock device requires KVM");
return;
}
kvm_update_clock(s);
qemu_add_vm_change_state_handler(kvmclock_vm_state_change, s);
}
static bool kvmclock_clock_is_reliable_needed(void *opaque)
{
KVMClockState *s = opaque;
return s->mach_use_reliable_get_clock;
}
static const VMStateDescription kvmclock_reliable_get_clock = {
.name = "kvmclock/clock_is_reliable",
.version_id = 1,
.minimum_version_id = 1,
.needed = kvmclock_clock_is_reliable_needed,
.fields = (VMStateField[]) {
VMSTATE_BOOL(clock_is_reliable, KVMClockState),
VMSTATE_END_OF_LIST()
}
};
/*
* When migrating, read the clock just before migration,
* so that the guest clock counts during the events
* between:
*
* * vm_stop()
* *
* * pre_save()
*
* This reduces kvmclock difference on migration from 5s
* to 0.1s (when max_downtime == 5s), because sending the
* final pages of memory (which happens between vm_stop()
* and pre_save()) takes max_downtime.
*/
static void kvmclock_pre_save(void *opaque)
{
KVMClockState *s = opaque;
kvm_update_clock(s);
}
static const VMStateDescription kvmclock_vmsd = {
.name = "kvmclock",
.version_id = 1,
.minimum_version_id = 1,
.pre_save = kvmclock_pre_save,
.fields = (VMStateField[]) {
VMSTATE_UINT64(clock, KVMClockState),
VMSTATE_END_OF_LIST()
},
.subsections = (const VMStateDescription * []) {
&kvmclock_reliable_get_clock,
NULL
}
};
static Property kvmclock_properties[] = {
DEFINE_PROP_BOOL("x-mach-use-reliable-get-clock", KVMClockState,
mach_use_reliable_get_clock, true),
DEFINE_PROP_END_OF_LIST(),
};
static void kvmclock_class_init(ObjectClass *klass, void *data)
{
DeviceClass *dc = DEVICE_CLASS(klass);
dc->realize = kvmclock_realize;
dc->vmsd = &kvmclock_vmsd;
dc->props = kvmclock_properties;
}
static const TypeInfo kvmclock_info = {
.name = TYPE_KVM_CLOCK,
.parent = TYPE_SYS_BUS_DEVICE,
.instance_size = sizeof(KVMClockState),
.class_init = kvmclock_class_init,
};
/* Note: Must be called after VCPU initialization. */
void kvmclock_create(void)
{
X86CPU *cpu = X86_CPU(first_cpu);
if (kvm_enabled() &&
cpu->env.features[FEAT_KVM] & ((1ULL << KVM_FEATURE_CLOCKSOURCE) |
(1ULL << KVM_FEATURE_CLOCKSOURCE2))) {
sysbus_create_simple(TYPE_KVM_CLOCK, -1, NULL);
}
}
static void kvmclock_register_types(void)
{
type_register_static(&kvmclock_info);
}
type_init(kvmclock_register_types)
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