linux-kernel - Re: [PATCH 2/4 V16] Add functions to check if the host has stopped the vm

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Date:	Wed, 14 Mar 2012 11:12:35 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Eric B Munson <emunson@...bm.net>
CC:	avi@...hat.com, mingo@...hat.com, hpa@...or.com,
	ryanh@...ux.vnet.ibm.com, aliguori@...ibm.com, mtosatti@...hat.com,
	kvm@...r.kernel.org, linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4 V16] Add functions to check if the host has stopped
 the vm

On 2012-03-10 20:37, 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.
> 

...

> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index f8492da..4ba090c 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -22,6 +22,7 @@
>  #include <asm/msr.h>
>  #include <asm/apic.h>
>  #include <linux/percpu.h>
> +#include <linux/hardirq.h>
>  
>  #include <asm/x86_init.h>
>  #include <asm/reboot.h>
> @@ -114,6 +115,26 @@ static void kvm_get_preset_lpj(void)
>  	preset_lpj = lpj;
>  }
>  
> +bool kvm_check_and_clear_guest_paused(void)
> +{
> +	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 = &__get_cpu_var(hv_clock);
> +	if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
> +		__this_cpu_and(hv_clock.flags, ~PVCLOCK_GUEST_STOPPED);
> +		ret = true;
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(kvm_check_and_clear_guest_paused);

Which module is going to use this? I failed to find it, but I may have
missed something.

The actual reason for this reply: this patches causes a compiler warning
here, likely due to lacking include for EXPORT_SYMBOL_GPL:

  CC      arch/x86/kernel/kvmclock.o
/data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: data
definition has no type or storage class
/data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: type defaults
to ‘int’ in declaration of ‘EXPORT_SYMBOL_GPL’
/data/linux-kvm/arch/x86/kernel/kvmclock.c:136:1: warning: parameter
names (without types) in function declaration

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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