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SubjectRe: [PATCH 2/6 V2] Add functions to check if the host has stopped the vm
On 10/31/2011 03:07 PM, Eric B Munson wrote:
> When a host stops or suspends a VM it will set a flag to show this. The
> watchdog will use these functions to determine if a softlockup is real, or the
> result of a suspended VM.
>
> Signed-off-by: Eric B Munson<emunson@mgebm.net>
> ---
> arch/x86/include/asm/pvclock.h | 2 ++
> arch/x86/kernel/kvmclock.c | 19 +++++++++++++++++++
> 2 files changed, 21 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
> index c59cc97..7d3ba41 100644
> --- a/arch/x86/include/asm/pvclock.h
> +++ b/arch/x86/include/asm/pvclock.h
> @@ -13,6 +13,8 @@ void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
> struct timespec *ts);
> void pvclock_resume(void);
>
> +bool kvm_check_and_clear_host_stopped(int cpu);

A kvm-specific function shouldn't be declared in pvclock.h as this is shared
code between KVM and Xen.

> +
> /*
> * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
> * yielding a 64-bit result.
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index c1a0188..8ddcfaf 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -113,6 +113,25 @@ static void kvm_get_preset_lpj(void)
> preset_lpj = lpj;
> }
>
> +bool kvm_check_and_clear_host_stopped(int cpu)
> +{
> + bool ret = false;
> + struct pvclock_vcpu_time_info *src;
> +
> + /*
> + * per_cpu() is safe here because this function is only called from
> + * timer functions where preemption is already disabled.
> + */
> + WARN_ON(!in_atomic());
> + src =&per_cpu(hv_clock, cpu);
> + if ((src->flags& PVCLOCK_GUEST_STOPPED) != 0) {
> + src->flags = src->flags& (~PVCLOCK_GUEST_STOPPED);
> + ret = true;
> + }

It would be helpful to separate out the patches for guest enablement from host
enablement. This is a guest function, correct?

Don't you need an atomic getandset here? Can the host clear this flag or only
set it?

It's ashame we don't have a proper pvclock spec in Documentation/. I would
suggest at least adding a description of how this bit works in the first patch.

Regards,

Anthony Liguori

> +
> + return ret;
> +}
> +
> static struct clocksource kvm_clock = {
> .name = "kvm-clock",
> .read = kvm_clock_get_cycles,



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