[PATCH] x86/xen: Disable APIC PM for Xen PV guests

[PATCH] x86/xen: Disable APIC PM for Xen PV guests

[Boris Ostrovsky]

Xen PV guests support only few APIC registers and writes to
unsupported registers result in WARN_ONs. Most APIC accesses in these
guests  have been eliminated; however, lapic_suspend/resume are still
called (on 32-bit kernels).

We can disable APIC power management in xen_smp_prepare_boot_cpu()
(which is called after APIC has been initialized).

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 arch/x86/include/asm/apic.h |    2 ++
 arch/x86/kernel/apic/apic.c |    6 ++++++
 arch/x86/xen/smp.c          |    4 ++++
 3 files changed, 12 insertions(+)


An alternative could be to add another op to stuct apic. The advantage would be
the fact that we never have a window of time when APIC PM is enabled. The downside
is having yet another op (of which there are already plenty).

We could also avoid loading lapic_syscore_ops but I couldn't think of a good way
to figure out when not to do it.



diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 1d2091a..1f100f2 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -687,6 +687,8 @@ extern int default_cpu_present_to_apicid(int mps_cpu);
 extern int default_check_phys_apicid_present(int phys_apicid);
 #endif
 
+extern void apic_pm_deactivate(void);
+
 #endif /* CONFIG_X86_LOCAL_APIC */
 extern void irq_enter(void);
 extern void irq_exit(void);
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 7f26c9a..60607b3 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2424,6 +2424,11 @@ static void apic_pm_activate(void)
 	apic_pm_state.active = 1;
 }
 
+void apic_pm_deactivate(void)
+{
+	apic_pm_state.active = 0;
+}
+
 static int __init init_lapic_sysfs(void)
 {
 	/* XXX: remove suspend/resume procs if !apic_pm_state.active? */
@@ -2439,6 +2444,7 @@ core_initcall(init_lapic_sysfs);
 #else	/* CONFIG_PM */
 
 static void apic_pm_activate(void) { }
+void apic_pm_deactivate(void) { }
 
 #endif	/* CONFIG_PM */
 
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index a18eadd..33115d8 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -298,6 +298,10 @@ static void __init xen_smp_prepare_boot_cpu(void)
 
 		xen_filter_cpu_maps();
 		xen_setup_vcpu_info_placement();
+
+#ifdef CONFIG_X86_LOCAL_APIC
+		apic_pm_deactivate();
+#endif
 	}
 	/*
 	 * The alternative logic (which patches the unlock/lock) runs before
-- 
1.7.10.4

Re: [PATCH] x86/xen: Disable APIC PM for Xen PV guests

[David Vrabel]

On 04/03/14 02:40, Boris Ostrovsky wrote:
> Xen PV guests support only few APIC registers and writes to
> unsupported registers result in WARN_ONs. Most APIC accesses in these
> guests  have been eliminated; however, lapic_suspend/resume are still
> called (on 32-bit kernels).
> 
> We can disable APIC power management in xen_smp_prepare_boot_cpu()
> (which is called after APIC has been initialized).

Having looked at another APIC related problem recently, I wonder if Xen
would be better served by having its own APIC driver instead of trying
to piggy-back of some hardware one which doesn't do what we want.

David

> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> ---
>  arch/x86/include/asm/apic.h |    2 ++
>  arch/x86/kernel/apic/apic.c |    6 ++++++
>  arch/x86/xen/smp.c          |    4 ++++
>  3 files changed, 12 insertions(+)
> 
> 
> An alternative could be to add another op to stuct apic. The advantage would be
> the fact that we never have a window of time when APIC PM is enabled. The downside
> is having yet another op (of which there are already plenty).
> 
> We could also avoid loading lapic_syscore_ops but I couldn't think of a good way
> to figure out when not to do it.
> 
> 
> 
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index 1d2091a..1f100f2 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -687,6 +687,8 @@ extern int default_cpu_present_to_apicid(int mps_cpu);
>  extern int default_check_phys_apicid_present(int phys_apicid);
>  #endif
>  
> +extern void apic_pm_deactivate(void);
> +
>  #endif /* CONFIG_X86_LOCAL_APIC */
>  extern void irq_enter(void);
>  extern void irq_exit(void);
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 7f26c9a..60607b3 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -2424,6 +2424,11 @@ static void apic_pm_activate(void)
>  	apic_pm_state.active = 1;
>  }
>  
> +void apic_pm_deactivate(void)
> +{
> +	apic_pm_state.active = 0;
> +}
> +
>  static int __init init_lapic_sysfs(void)
>  {
>  	/* XXX: remove suspend/resume procs if !apic_pm_state.active? */
> @@ -2439,6 +2444,7 @@ core_initcall(init_lapic_sysfs);
>  #else	/* CONFIG_PM */
>  
>  static void apic_pm_activate(void) { }
> +void apic_pm_deactivate(void) { }
>  
>  #endif	/* CONFIG_PM */
>  
> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index a18eadd..33115d8 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -298,6 +298,10 @@ static void __init xen_smp_prepare_boot_cpu(void)
>  
>  		xen_filter_cpu_maps();
>  		xen_setup_vcpu_info_placement();
> +
> +#ifdef CONFIG_X86_LOCAL_APIC
> +		apic_pm_deactivate();
> +#endif
>  	}
>  	/*
>  	 * The alternative logic (which patches the unlock/lock) runs before

Re: [PATCH] x86/xen: Disable APIC PM for Xen PV guests

[Boris Ostrovsky]

On 03/04/2014 05:25 AM, David Vrabel wrote:
> On 04/03/14 02:40, Boris Ostrovsky wrote:
>> Xen PV guests support only few APIC registers and writes to
>> unsupported registers result in WARN_ONs. Most APIC accesses in these
>> guests  have been eliminated; however, lapic_suspend/resume are still
>> called (on 32-bit kernels).
>>
>> We can disable APIC power management in xen_smp_prepare_boot_cpu()
>> (which is called after APIC has been initialized).
> Having looked at another APIC related problem recently, I wonder if Xen
> would be better served by having its own APIC driver instead of trying
> to piggy-back of some hardware one which doesn't do what we want.

Possibly, although I don't think it will help with this particular issue 
since this patch is trying to address a problem in non-privileged 
guests. Such guests don't have ACPI enabled and so no APIC probing is 
done for them.

-boris

>
> David
>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> ---
>>   arch/x86/include/asm/apic.h |    2 ++
>>   arch/x86/kernel/apic/apic.c |    6 ++++++
>>   arch/x86/xen/smp.c          |    4 ++++
>>   3 files changed, 12 insertions(+)
>>
>>
>> An alternative could be to add another op to stuct apic. The advantage would be
>> the fact that we never have a window of time when APIC PM is enabled. The downside
>> is having yet another op (of which there are already plenty).
>>
>> We could also avoid loading lapic_syscore_ops but I couldn't think of a good way
>> to figure out when not to do it.
>>
>>
>>
>> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
>> index 1d2091a..1f100f2 100644
>> --- a/arch/x86/include/asm/apic.h
>> +++ b/arch/x86/include/asm/apic.h
>> @@ -687,6 +687,8 @@ extern int default_cpu_present_to_apicid(int mps_cpu);
>>   extern int default_check_phys_apicid_present(int phys_apicid);
>>   #endif
>>   
>> +extern void apic_pm_deactivate(void);
>> +
>>   #endif /* CONFIG_X86_LOCAL_APIC */
>>   extern void irq_enter(void);
>>   extern void irq_exit(void);
>> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
>> index 7f26c9a..60607b3 100644
>> --- a/arch/x86/kernel/apic/apic.c
>> +++ b/arch/x86/kernel/apic/apic.c
>> @@ -2424,6 +2424,11 @@ static void apic_pm_activate(void)
>>   	apic_pm_state.active = 1;
>>   }
>>   
>> +void apic_pm_deactivate(void)
>> +{
>> +	apic_pm_state.active = 0;
>> +}
>> +
>>   static int __init init_lapic_sysfs(void)
>>   {
>>   	/* XXX: remove suspend/resume procs if !apic_pm_state.active? */
>> @@ -2439,6 +2444,7 @@ core_initcall(init_lapic_sysfs);
>>   #else	/* CONFIG_PM */
>>   
>>   static void apic_pm_activate(void) { }
>> +void apic_pm_deactivate(void) { }
>>   
>>   #endif	/* CONFIG_PM */
>>   
>> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
>> index a18eadd..33115d8 100644
>> --- a/arch/x86/xen/smp.c
>> +++ b/arch/x86/xen/smp.c
>> @@ -298,6 +298,10 @@ static void __init xen_smp_prepare_boot_cpu(void)
>>   
>>   		xen_filter_cpu_maps();
>>   		xen_setup_vcpu_info_placement();
>> +
>> +#ifdef CONFIG_X86_LOCAL_APIC
>> +		apic_pm_deactivate();
>> +#endif
>>   	}
>>   	/*
>>   	 * The alternative logic (which patches the unlock/lock) runs before

Re: [PATCH] x86/xen: Disable APIC PM for Xen PV guests

[Boris Ostrovsky]

On 03/03/2014 09:40 PM, Boris Ostrovsky wrote:
> Xen PV guests support only few APIC registers and writes to
> unsupported registers result in WARN_ONs. Most APIC accesses in these
> guests  have been eliminated; however, lapic_suspend/resume are still
> called (on 32-bit kernels).
>
> We can disable APIC power management in xen_smp_prepare_boot_cpu()
> (which is called after APIC has been initialized).


This touches generic APIC code so x86 maintainers' review would
be appreciated.

Thanks.
-boris


> Signed-off-by: Boris Ostrovsky<boris.ostrovsky@oracle.com>
> ---
>   arch/x86/include/asm/apic.h |    2 ++
>   arch/x86/kernel/apic/apic.c |    6 ++++++
>   arch/x86/xen/smp.c          |    4 ++++
>   3 files changed, 12 insertions(+)
>
>
> An alternative could be to add another op to stuct apic. The advantage would be
> the fact that we never have a window of time when APIC PM is enabled. The downside
> is having yet another op (of which there are already plenty).
>
> We could also avoid loading lapic_syscore_ops but I couldn't think of a good way
> to figure out when not to do it.
>
>
>
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index 1d2091a..1f100f2 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -687,6 +687,8 @@ extern int default_cpu_present_to_apicid(int mps_cpu);
>   extern int default_check_phys_apicid_present(int phys_apicid);
>   #endif
>   
> +extern void apic_pm_deactivate(void);
> +
>   #endif /* CONFIG_X86_LOCAL_APIC */
>   extern void irq_enter(void);
>   extern void irq_exit(void);
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 7f26c9a..60607b3 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -2424,6 +2424,11 @@ static void apic_pm_activate(void)
>   	apic_pm_state.active = 1;
>   }
>   
> +void apic_pm_deactivate(void)
> +{
> +	apic_pm_state.active = 0;
> +}
> +
>   static int __init init_lapic_sysfs(void)
>   {
>   	/* XXX: remove suspend/resume procs if !apic_pm_state.active? */
> @@ -2439,6 +2444,7 @@ core_initcall(init_lapic_sysfs);
>   #else	/* CONFIG_PM */
>   
>   static void apic_pm_activate(void) { }
> +void apic_pm_deactivate(void) { }
>   
>   #endif	/* CONFIG_PM */
>   
> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index a18eadd..33115d8 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -298,6 +298,10 @@ static void __init xen_smp_prepare_boot_cpu(void)
>   
>   		xen_filter_cpu_maps();
>   		xen_setup_vcpu_info_placement();
> +
> +#ifdef CONFIG_X86_LOCAL_APIC
> +		apic_pm_deactivate();
> +#endif
>   	}
>   	/*
>   	 * The alternative logic (which patches the unlock/lock) runs before