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

[Jan Kiszka]

On 2011-02-07 14:40, Glauber Costa wrote:
> On Mon, 2011-02-07 at 13:36 +0100, Jan Kiszka wrote:
>> On 2011-02-07 13:27, Glauber Costa wrote:
>>> On Mon, 2011-02-07 at 12:19 +0100, Jan Kiszka 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 <address@hidden>
>>>> CC: Glauber Costa <address@hidden>
>>>> ---
>>>>  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
>>>>  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        <address@hidden>
>>>> + *
>>>> + * 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);
>>>> +    }
>>>> +}
>>>> +
>>>> +static void kvmclock_register_device(void)
>>>> +{
>>>> +    if (kvm_enabled()) {
>>>> +        sysbus_register_withprop(&kvmclock_info);
>>>> +    }
>>>> +}
>>>> +
>>>> +device_init(kvmclock_register_device);
>>>> +
>>>> +#else /* !(CONFIG_KVM_PARA && KVM_CAP_ADJUST_CLOCK) */
>>>> +
>>>> +void kvmclock_create(void)
>>>> +{
>>>> +}
>>>> +#endif /* !(CONFIG_KVM_PARA && KVM_CAP_ADJUST_CLOCK) */
>>>> diff --git a/hw/kvmclock.h b/hw/kvmclock.h
>>>> new file mode 100644
>>>> index 0000000..7a83cbe
>>>> --- /dev/null
>>>> +++ b/hw/kvmclock.h
>>>> @@ -0,0 +1,14 @@
>>>> +/*
>>>> + * QEMU KVM support, paravirtual clock device
>>>> + *
>>>> + * Copyright (C) 2011 Siemens AG
>>>> + *
>>>> + * Authors:
>>>> + *  Jan Kiszka        <address@hidden>
>>>> + *
>>>> + * This work is licensed under the terms of the GNU GPL version 2.
>>>> + * See the COPYING file in the top-level directory.
>>>> + *
>>>> + */
>>>> +
>>>> +void kvmclock_create(void);
>>>> diff --git a/hw/pc_piix.c b/hw/pc_piix.c
>>>> index 7b74473..9bc4659 100644
>>>> --- a/hw/pc_piix.c
>>>> +++ b/hw/pc_piix.c
>>>> @@ -32,6 +32,7 @@
>>>>  #include "boards.h"
>>>>  #include "ide.h"
>>>>  #include "kvm.h"
>>>> +#include "kvmclock.h"
>>>>  #include "sysemu.h"
>>>>  #include "sysbus.h"
>>>>  #include "arch_init.h"
>>>> @@ -66,7 +67,8 @@ static void pc_init1(ram_addr_t ram_size,
>>>>                       const char *kernel_cmdline,
>>>>                       const char *initrd_filename,
>>>>                       const char *cpu_model,
>>>> -                     int pci_enabled)
>>>> +                     int pci_enabled,
>>>> +                     int kvmclock_enabled)
>>>>  
>>> What exactly is your motivation to that ? I think mid/long-term
>>> we should be making machine initialization more common among
>>> architectures, not introducing more arch specific, or even worse, kvm
>>> specific parameters here.
>>>
>>> I'd like to understand what do we gain from that, since opting kvmclock
>>> in our out is done by cpuid anyway - no need for a specific machine.
>>
>> Is that really the case? I thought we were already shipping versions
>> where that CPU feature was enabled by default. If not, I'll happily drop
>> that admittedly clumsy approach above.
> 
> Yes, AFAIK, kvmclock is enabled by default, disabled by cpuid-leaf, as
> in
> -cpu kvm64,-kvmclock
> 
> So your test for cpuid bit before starting kvmclock should already cover
> it.
> 

No, just the contrary: As kvmclock was always enabled in older versions
and the compat machines also expose it, we cannot rely on the flag to
enable this new (and therefore 0.15-only) vmstate.

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux