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

[Glauber Costa]

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.