kvmclock.c

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/*  KVM paravirtual clock driver. A clocksource implementation
    Copyright (C) 2008 Glauber de Oliveira Costa, Red Hat Inc.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include <linux/clocksource.h>
#include <linux/kvm_para.h>
#include <asm/pvclock.h>
#include <asm/msr.h>
#include <asm/apic.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>

#include <asm/x86_init.h>
#include <asm/reboot.h>

static int kvmclock = 1;
static int msr_kvm_system_time = MSR_KVM_SYSTEM_TIME;
static int msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK;

static int parse_no_kvmclock(char *arg)
{
    kvmclock = 0;
    return 0;
}
early_param("no-kvmclock", parse_no_kvmclock);

/* The hypervisor will put information about time periodically here */
static DEFINE_PER_CPU_SHARED_ALIGNED(struct pvclock_vcpu_time_info, hv_clock);
static struct pvclock_wall_clock wall_clock;

/*
 * 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
 * that with system time
 */
static unsigned long kvm_get_wallclock(void)
{
    struct pvclock_vcpu_time_info *vcpu_time;
    struct timespec ts;
    int low, high;

    low = (int)__pa_symbol(&wall_clock);
    high = ((u64)__pa_symbol(&wall_clock) >> 32);

    native_write_msr(msr_kvm_wall_clock, low, high);

    vcpu_time = &get_cpu_var(hv_clock);
    pvclock_read_wallclock(&wall_clock, vcpu_time, &ts);
    put_cpu_var(hv_clock);

    return ts.tv_sec;
}

static int kvm_set_wallclock(unsigned long now)
{
    return -1;
}

static cycle_t kvm_clock_read(void)
{
    struct pvclock_vcpu_time_info *src;
    cycle_t ret;

    preempt_disable_notrace();
    src = &__get_cpu_var(hv_clock);
    ret = pvclock_clocksource_read(src);
    preempt_enable_notrace();
    return ret;
}

static cycle_t kvm_clock_get_cycles(struct clocksource *cs)
{
    return kvm_clock_read();
}

/*
 * If we don't do that, there is the possibility that the guest
 * will calibrate under heavy load - thus, getting a lower lpj -
 * and execute the delays themselves without load. This is wrong,
 * because no delay loop can finish beforehand.
 * Any heuristics is subject to fail, because ultimately, a large
 * poll of guests can be running and trouble each other. So we preset
 * lpj here
 */
static unsigned long kvm_get_tsc_khz(void)
{
    struct pvclock_vcpu_time_info *src;
    src = &per_cpu(hv_clock, 0);
    return pvclock_tsc_khz(src);
}

static void kvm_get_preset_lpj(void)
{
    unsigned long khz;
    u64 lpj;

    khz = kvm_get_tsc_khz();

    lpj = ((u64)khz * 1000);
    do_div(lpj, HZ);
    preset_lpj = lpj;
}

bool kvm_check_and_clear_guest_paused(void)
{
    bool ret = false;
    struct pvclock_vcpu_time_info *src;

    src = &__get_cpu_var(hv_clock);
    if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
        __this_cpu_and(hv_clock.flags, ~PVCLOCK_GUEST_STOPPED);
        ret = true;
    }

    return ret;
}

static struct clocksource kvm_clock = {
    .name = "kvm-clock",
    .read = kvm_clock_get_cycles,
    .rating = 400,
    .mask = CLOCKSOURCE_MASK(64),
    .flags = CLOCK_SOURCE_IS_CONTINUOUS,
};

int kvm_register_clock(char *txt)
{
    int cpu = smp_processor_id();
    int low, high, ret;

    low = (int)__pa(&per_cpu(hv_clock, cpu)) | 1;
    high = ((u64)__pa(&per_cpu(hv_clock, cpu)) >> 32);
    ret = native_write_msr_safe(msr_kvm_system_time, low, high);
    printk(KERN_INFO "kvm-clock: cpu %d, msr %x:%x, %s\n",
           cpu, high, low, txt);

    return ret;
}

static void kvm_save_sched_clock_state(void)
{
}

static void kvm_restore_sched_clock_state(void)
{
    kvm_register_clock("primary cpu clock, resume");
}

#ifdef CONFIG_X86_LOCAL_APIC
static void __cpuinit 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"));
}
#endif

/*
 * After the clock is registered, the host will keep writing to the
 * registered memory location. If the guest happens to shutdown, this memory
 * won't be valid. In cases like kexec, in which you install a new kernel, this
 * means a random memory location will be kept being written. So before any
 * kind of shutdown from our side, we unregister the clock by writting anything
 * that does not have the 'enable' bit set in the msr
 */
#ifdef CONFIG_KEXEC
static void kvm_crash_shutdown(struct pt_regs *regs)
{
    native_write_msr(msr_kvm_system_time, 0, 0);
    kvm_disable_steal_time();
    native_machine_crash_shutdown(regs);
}
#endif

static void kvm_shutdown(void)
{
    native_write_msr(msr_kvm_system_time, 0, 0);
    kvm_disable_steal_time();
    native_machine_shutdown();
}

void __init kvmclock_init(void)
{
    if (!kvm_para_available())
        return;

    if (kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
        msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW;
        msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW;
    } else if (!(kvmclock && kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE)))
        return;

    printk(KERN_INFO "kvm-clock: Using msrs %x and %x",
        msr_kvm_system_time, msr_kvm_wall_clock);

    if (kvm_register_clock("boot clock"))
        return;
    pv_time_ops.sched_clock = kvm_clock_read;
    x86_platform.calibrate_tsc = kvm_get_tsc_khz;
    x86_platform.get_wallclock = kvm_get_wallclock;
    x86_platform.set_wallclock = kvm_set_wallclock;
#ifdef CONFIG_X86_LOCAL_APIC
    x86_cpuinit.early_percpu_clock_init =
        kvm_setup_secondary_clock;
#endif
    x86_platform.save_sched_clock_state = kvm_save_sched_clock_state;
    x86_platform.restore_sched_clock_state = kvm_restore_sched_clock_state;
    machine_ops.shutdown  = kvm_shutdown;
#ifdef CONFIG_KEXEC
    machine_ops.crash_shutdown  = kvm_crash_shutdown;
#endif
    kvm_get_preset_lpj();
    clocksource_register_hz(&kvm_clock, NSEC_PER_SEC);
    pv_info.paravirt_enabled = 1;
    pv_info.name = "KVM";

    if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
        pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
}