Re: [PATCH v6 18/29] xen/x86: allow disabling the emulated pmu

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

On 09/25/2015 11:22 AM, Roger Pau Monné wrote:
> El 25/09/15 a les 17.13, Jan Beulich ha escrit:
>>>>> On 25.09.15 at 17:07, <roger.pau@citrix.com> wrote:
>>> El 21/09/15 a les 16.48, Boris Ostrovsky ha escrit:
>>>> On 09/21/2015 10:36 AM, Jan Beulich wrote:
>>>>>>>> On 04.09.15 at 14:08, <roger.pau@citrix.com> wrote:
>>>>> Hmm - this seems questionable to me: Isn't the vPMU an optional
>>>>> feature anyway? I.e. doesn't need separate handling here? Boris?
>>>> It is optional system-wise, not per-guest, which is what I think Roger
>>>> is trying to do. I in fact wanted to add ability to disable VPMU per
>>>> guest myself.
>>>>
>>>> However, VPMU has nothing to do with device model so I don't think it
>>>> should be part of this series from that perspective.
>>> vpmu is enabled globally on the xen command line, there's no way to
>>> disable it on a per-guest basis, so AFAICS it will be enabled for
>>> HMVlite guests which is wrong because we don't have a vlapic.
>> Hmm, Boris specifically enabled vPMU to be available to all three
>> kinds of guests, and PVH in it s current shape doesn't have a
>> vLAPIC either. So making such a connection seems wrong to me.
> IMHO, I would prefer the vPMU support in HVMlite guests to be tied to a
> vlapic presence, so we can do it the HVM way instead of having to do
> hypercalls.
>
> One think that could work is changing the is_hvm_* calls in vpmu.c to
> has_vlapic. This way HVMlite guests could still use the PV vPMU
> interface, but once a lapic is enabled we could use the native way.

Yes, I think that would work.

-boris