Re: [Xen-devel] [PATCH v13 for-xen-4.5 07/21] x86/VPMU: Handle APIC_LVTPC accesses

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.10.14 at 20:05, <boris.ostrovsky@xxxxxxxxxx> wrote:
> On 10/13/2014 09:02 AM, Jan Beulich wrote:
>>>>> On 03.10.14 at 23:40, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>> @@ -706,10 +693,6 @@ static int core2_vpmu_do_interrupt(struct 
>>> cpu_user_regs *regs)
>>>               return 0;
>>>       }
>>>   
>>> -    /* HW sets the MASK bit when performance counter interrupt occurs*/
>>> -    vpmu->hw_lapic_lvtpc = apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED;
>>> -    apic_write_around(APIC_LVTPC, vpmu->hw_lapic_lvtpc);
>> So why is simply deleting this correct? The comment makes pretty
>> clear why it was being done here. All I could see being valid without
>> further explanation is the removal of the middle of the three lines.
> 
> It is expected that PMU interrupt will set the mask bit so whoever is 
> using PMU hardware (bare-metal or virtualized) is expected to clear it. 
> Therefore there is no reason for the hypervisor to do this.

Makes sense.

> I can add a note about it in the commit message.

Yes please.

Jan


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