Re: [PATCH v11 for-xen-4.5 13/20] x86/VPMU: Save VPMU state for PV guests during context switch

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 09/23/2014 11:01 AM, Konrad Rzeszutek Wilk wrote:
> On Mon, Sep 22, 2014 at 07:57:54PM -0400, Boris Ostrovsky wrote:
>> Save VPMU state during context switch for both HVM and PV(H) guests.
>>
>> A subsequent patch will make it possible for vpmu_switch_to() to call
> Could you say what is the name of the 'subsequent patch' in the commit
> description please?

It's patch 19 where NMI PMU interrupts are added.

>
>> vmx_vmcs_try_enter()->vcpu_pause() which needs is_running to be correctly
>> set/cleared. To prepare for that, call context_saved() before vpmu_switch_to()
>> is executed.
> And what ramifications does that have to the guests if one only applied
> patches up to this point?

None. Which is why I decided to make this change in this patch and not 
wait until patch 19.

-boris

>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> ---
>>   xen/arch/x86/domain.c | 20 +++++++++-----------
>>   1 file changed, 9 insertions(+), 11 deletions(-)
>>
>> diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
>> index 5e492d8..d7fb99d 100644
>> --- a/xen/arch/x86/domain.c
>> +++ b/xen/arch/x86/domain.c
>> @@ -1495,16 +1495,13 @@ void context_switch(struct vcpu *prev, struct vcpu *next)
>>       }
>>   
>>       if ( prev != next )
>> -        _update_runstate_area(prev);
>> -
>> -    if ( is_hvm_vcpu(prev) )
>>       {
>> -        if (prev != next)
>> -            vpmu_switch_from(prev, next);
>> +        _update_runstate_area(prev);
>> +        vpmu_switch_from(prev, next);
>> +    }
>>   
>> -        if ( !list_empty(&prev->arch.hvm_vcpu.tm_list) )
>> +    if ( is_hvm_vcpu(prev) && !list_empty(&prev->arch.hvm_vcpu.tm_list) )
>>               pt_save_timer(prev);
>> -    }
>>   
>>       local_irq_disable();
>>   
>> @@ -1543,15 +1540,16 @@ void context_switch(struct vcpu *prev, struct vcpu *next)
>>                              !is_hardware_domain(next->domain));
>>       }
>>   
>> -    if ( is_hvm_vcpu(prev) && (prev != next) )
>> -        /* Must be done with interrupts enabled */
>> -        vpmu_switch_to(prev, next);
>> -
>>       context_saved(prev);
>>   
>>       if ( prev != next )
>> +    {
>>           _update_runstate_area(next);
>>   
>> +        /* Must be done with interrupts enabled */
>> +        vpmu_switch_to(prev, next);
>> +    }
>> +
>>       /* Ensure that the vcpu has an up-to-date time base. */
>>       update_vcpu_system_time(next);
>>   
>> -- 
>> 1.8.1.4
>>
>>
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