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

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Date:	Thu, 15 Mar 2012 18:14:45 -0400
From:	Eric B Munson <emunson@...bm.net>
To:	Jan Kiszka <jan.kiszka@...mens.com>
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 Wed, 14 Mar 2012 11:12:35 +0100, Jan Kiszka wrote:
> 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


There isn't a module that will use it, I was under the (mistaken) 
understanding that
the EXPORT was necessary for use in kernel/watchdog.c.  Give that it 
isn't, I will
post a patch to remove it shortly.

Eric
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