Re: [PATCH v12 for-xen-4.5 11/20] x86/VPMU: Interface for setting PMU mode and flags

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

On 09/26/2014 05:04 PM, Tian, Kevin wrote:
>> From: Boris Ostrovsky [mailto:boris.ostrovsky@oracle.com]
>> Sent: Thursday, September 25, 2014 12:29 PM
>>
>> Add runtime interface for setting PMU mode and flags. Three main modes are
>> provided:
>> * XENPMU_MODE_OFF:  PMU is not virtualized
>> * XENPMU_MODE_SELF: Guests can access PMU MSRs and receive PMU
>> interrupts.
>> * XENPMU_MODE_HV: Same as XENPMU_MODE_SELF for non-proviledged
>> guests, dom0
>>    can profile itself and the hypervisor.
>>
>> Note that PMU modes are different from what can be provided at Xen's boot
>> line
>> with 'vpmu' argument. An 'off' (or '0') value is equivalent to
>> XENPMU_MODE_OFF.
>> Any other value, on the other hand, will cause VPMU mode to be set to
>> XENPMU_MODE_SELF during boot.
>>
>> For feature flags only Intel's BTS is currently supported.
>>
>> Mode and flags are set via HYPERVISOR_xenpmu_op hypercall.
>>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> I'll need focused time to review this one and several latter big patches, which
> can't be afforded this week. Will do that next week.

Thank you.

>
> One immediate comment though. Looks below comment is not fixed
> which you said is for XENPMU_MODE_ALL:


XENPMU_MODE_ALL is defined later, in patch 18, and the 'if' below is 
updated there.

(and I think when I said earlier that the comment was incorrect I was 
wrong. I re-read it and I don't see anything wrong with it. I may have 
been thinking about the 'if' statement not being correct, not realizing 
that it is updated by the later patch).


-boris

>
>> +        if ( vpmu_mode == XENPMU_MODE_OFF )
>> +        {
>> +            /*
>> +             * Make sure all (non-dom0) VCPUs have unloaded their
>> VPMUs. This
>> +             * can be achieved by having all physical processors go
>> through
>> +             * context_switch().
>> +             */
>> +            ret = vpmu_force_context_switch();
>> +            if ( ret )
>> +                vpmu_mode = current_mode;
>> +        }
>> +
>> +        spin_unlock(&xenpmu_mode_lock);
>> +        break;
>> +    }
>> +
> Thanks
> Kevin