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

[Jan Kiszka <jan.kiszka@siemens.com>]

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 <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
>>  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);
>> +    }
>> +}
>> +
>> +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        <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.
>> + *
>> + */
>> +
>> +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.

Jan

-- 
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