Re: [Xen-devel] [PATCH v11 for-xen-4.5 11/20] x86/VPMU: Interface for setting PMU mode and flags

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 09/23/2014 03:24 PM, Boris Ostrovsky wrote:
> On 09/23/2014 02:58 PM, Konrad Rzeszutek Wilk wrote:
> > On Mon, Sep 22, 2014 at 07:57:52PM -0400, Boris Ostrovsky wrote:
> > > 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.
> > I forgot to mention that we should probably also include the XSM calls.
> > (And CC the maintainer of it).
> >
> > For examples, see the claim (919f59b3b99e1d845c6a1f30125e79e828805d87) or
> > vnmua (40c7af684fc0bf89c7b643a5492b4abd920fba86) patches.
> (+ Daniel)
>
> I haven't looked at XSM in a few months but I remember when I tried to use XSM 
> for this I found that we ran out of bits for a new hypercall in the permission 
> vector. (I actually mention this in the cover letter, but it's way way down)
>
> The two commits that you refer to are using existing hypercalls.
>
> -boris
The solution to running out of bits is to create another class in order to
hold the new permissions, as has already been done for domain/domain2.  The
CQM patches (v15 03/11) already define a class xen2, so you may want to base
on top of it so that patches don't conflict (or whatever is preferred based
on the patchesets' relative readiness).

--
Daniel De Graaf
National Security Agency

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