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kvmclock: clock should count only if vm is running 

kvmclock should not count while vm is paused, because:

1) if the vm is paused for long periods, timekeeping
math can overflow while converting the (large) clocksource
delta to nanoseconds.

2) Users rely on CLOCK_MONOTONIC to count run time, that is,
time which OS has been in a runnable state (see CLOCK_BOOTTIME).

Change kvmclock driver so as to save clock value when vm transitions
from runnable to stopped state, and to restore clock value from stopped
to runnable transition.

Cc: qemu-stable@nongnu.org
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Marcelo Tosatti 2013-06-18 20:38:25 -03:00 committed by Paolo Bonzini
parent bd50cbaa0f
commit 00f4d64ee7
1 changed files with 30 additions and 34 deletions
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64
hw/i386/kvm/clock.c
View File

@ -28,38 +28,6 @@ typedef struct KVMClockState {
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 = !runstate_is_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,
RunState state)
@ -70,8 +38,18 @@ static void kvmclock_vm_state_change(void *opaque, int running,
int ret;
if (running) {
struct kvm_clock_data data;
s->clock_valid = false;
data.clock = s->clock;
data.flags = 0;
ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);
if (ret < 0) {
fprintf(stderr, "KVM_SET_CLOCK failed: %s\n", strerror(ret));
abort();
}
if (!cap_clock_ctrl) {
return;
}
@ -84,6 +62,26 @@ static void kvmclock_vm_state_change(void *opaque, int running,
return;
}
}
} else {
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));
abort();
}
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 = true;
}
}
@ -100,8 +98,6 @@ static const VMStateDescription kvmclock_vmsd = {
.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()