Re: [PATCH] KVM guest: prevent tracing recursion with kvmclock

[Gleb Natapov <gleb@redhat.com>]

On Tue, Nov 15, 2011 at 03:01:15PM +0200, Avi Kivity wrote:
> Stop tracing when we read the clock, since tracing will also
> want to read the clock, and recurse indefinitely.
> 
> Based on a similar patch for Xen from Jeremy Fitzhardinge.
> 
> Signed-off-by: Avi Kivity <avi@redhat.com>
Tested-by: Gleb Natapov <gleb@redhat.com>

> ---
>  arch/x86/kernel/kvmclock.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index c1a0188..44842d7 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -74,9 +74,10 @@ static cycle_t kvm_clock_read(void)
>  	struct pvclock_vcpu_time_info *src;
>  	cycle_t ret;
>  
> -	src = &get_cpu_var(hv_clock);
> +	preempt_disable_notrace();
> +	src = &__get_cpu_var(hv_clock);
>  	ret = pvclock_clocksource_read(src);
> -	put_cpu_var(hv_clock);
> +	preempt_enable_notrace();
>  	return ret;
>  }
>  
> -- 
> 1.7.7.1

--
			Gleb.