Re: [Qemu-devel] [PATCH 15/15] kvm: x86: Introduce kvmclock device to save/restore its state

[Blue Swirl <blauwirbel@gmail.com>]

On Mon, Feb 7, 2011 at 1:19 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
> If kvmclock is used, which implies the kernel supports it, register a
> kvmclock device with the sysbus. Its main purpose is to save and restore
> the kernel state on migration, but this will also allow to visualize it
> one day.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> CC: Glauber Costa <glommer@redhat.com>
> ---
>  Makefile.target |    4 +-
>  hw/kvmclock.c   |  125 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  hw/kvmclock.h   |   14 ++++++
>  hw/pc_piix.c    |   31 +++++++++++---
>  4 files changed, 165 insertions(+), 9 deletions(-)
>  create mode 100644 hw/kvmclock.c
>  create mode 100644 hw/kvmclock.h
>
> diff --git a/Makefile.target b/Makefile.target
> index b0ba95f..30232fa 100644
> --- a/Makefile.target
> +++ b/Makefile.target
> @@ -37,7 +37,7 @@ ifndef CONFIG_HAIKU
>  LIBS+=-lm
>  endif
>
> -kvm.o kvm-all.o vhost.o vhost_net.o: QEMU_CFLAGS+=$(KVM_CFLAGS)
> +kvm.o kvm-all.o vhost.o vhost_net.o kvmclock.o: QEMU_CFLAGS+=$(KVM_CFLAGS)
>
>  config-target.h: config-target.h-timestamp
>  config-target.h-timestamp: config-target.mak
> @@ -218,7 +218,7 @@ obj-i386-y += cirrus_vga.o apic.o ioapic.o piix_pci.o
>  obj-i386-y += vmmouse.o vmport.o hpet.o applesmc.o
>  obj-i386-y += device-hotplug.o pci-hotplug.o smbios.o wdt_ib700.o
>  obj-i386-y += debugcon.o multiboot.o
> -obj-i386-y += pc_piix.o
> +obj-i386-y += pc_piix.o kvmclock.o

Please build kvmclock.o conditionally to CONFIG_something...

>  obj-i386-$(CONFIG_SPICE) += qxl.o qxl-logger.o qxl-render.o
>
>  # shared objects
> diff --git a/hw/kvmclock.c b/hw/kvmclock.c
> new file mode 100644
> index 0000000..b6ceddf
> --- /dev/null
> +++ b/hw/kvmclock.c
> @@ -0,0 +1,125 @@
> +/*
> + * 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.
> + *
> + */
> +
> +#include "qemu-common.h"
> +#include "sysemu.h"
> +#include "sysbus.h"
> +#include "kvm.h"
> +#include "kvmclock.h"
> +
> +#if defined(CONFIG_KVM_PARA) && defined(KVM_CAP_ADJUST_CLOCK)
> +
> +#include <linux/kvm.h>
> +#include <linux/kvm_para.h>
> +
> +typedef struct KVMClockState {
> +    SysBusDevice busdev;
> +    uint64_t clock;
> +    bool clock_valid;
> +} KVMClockState;
> +
> +static void kvmclock_pre_save(void *opaque)
> +{
> +    KVMClockState *s = opaque;
> +    struct kvm_clock_data data;
> +    int ret;
> +
> +    if (s->clock_valid) {
> +        return;
> +    }
> +    ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
> +    if (ret < 0) {
> +        fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret));
> +        data.clock = 0;
> +    }
> +    s->clock = data.clock;
> +    /*
> +     * 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 = !vm_running;
> +}
> +
> +static int kvmclock_post_load(void *opaque, int version_id)
> +{
> +    KVMClockState *s = opaque;
> +    struct kvm_clock_data data;
> +
> +    data.clock = s->clock;
> +    data.flags = 0;
> +    return kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);
> +}
> +
> +static void kvmclock_vm_state_change(void *opaque, int running, int reason)
> +{
> +    KVMClockState *s = opaque;
> +
> +    if (running) {
> +        s->clock_valid = false;
> +    }
> +}
> +
> +static int kvmclock_init(SysBusDevice *dev)
> +{
> +    KVMClockState *s = FROM_SYSBUS(KVMClockState, dev);
> +
> +    qemu_add_vm_change_state_handler(kvmclock_vm_state_change, s);
> +    return 0;
> +}
> +
> +static const VMStateDescription kvmclock_vmsd = {
> +    .name = "kvmclock",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .minimum_version_id_old = 1,
> +    .pre_save = kvmclock_pre_save,
> +    .post_load = kvmclock_post_load,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UINT64(clock, KVMClockState),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
> +static SysBusDeviceInfo kvmclock_info = {
> +    .qdev.name = "kvmclock",
> +    .qdev.size = sizeof(KVMClockState),
> +    .qdev.vmsd = &kvmclock_vmsd,
> +    .qdev.no_user = 1,
> +    .init = kvmclock_init,
> +};
> +
> +/* Note: Must be called after VCPU initialization. */
> +void kvmclock_create(void)
> +{
> +    if (kvm_enabled() &&
> +        first_cpu->cpuid_kvm_features & (1ULL << KVM_FEATURE_CLOCKSOURCE)) {
> +        sysbus_create_simple("kvmclock", -1, NULL);
> +    }
> +}

... and with this moved to a header as a static inline function, it
should be possible to use sysbus_try_create() (coming soon) to try to
create the device. Then it's not fatal if the device can't be created,
that just means that the capability was not available at build time.