Re: [PATCH 15/21] libs/guest: obtain a compatible cpu policy from two input ones

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Apr 01, 2021 at 05:26:03PM +0100, Andrew Cooper wrote:
> On 23/03/2021 09:58, Roger Pau Monne wrote:
> > Introduce a helper to obtain a compatible cpu policy based on two
> > input cpu policies. Currently this is done by and'ing all CPUID leaves
> > and MSR entries, except for MSR_ARCH_CAPABILITIES which has the RSBA
> > bit or'ed.
> >
> > The _AC macro is pulled from libxl_internal.h into xen-tools/libs.h
> > since it's required in order to use the msr-index.h header.
> >
> > Note there's no need to place this helper in libx86, since the
> > calculation of a compatible policy shouldn't be done from the
> > hypervisor.
> >
> > No callers of the interface introduced.
> >
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> 
> I think this wants to be in libx86, because we'll want it to replace the
> opencoded derivation logic in init_cpuid()

I think you mean init_domain_cpuid_policy or recalculate_cpuid_policy?
I cannot find any init_cpuid.

I'm not convinced we need this in libx86 for the hypervisor, as I
don't know exactly how we would use it there. I expect the hypervisor
to validate policies provided by the toolstack, but not for it to
create such policies unless for very specific domains (ie: dom0 or
similar) which shouldn't require any leveling.

I'm happy to place it libx86, but I think I need to understand better
why it needs to be there.

> Also, we absolutely want to unit test it.  (I could have sworn I already
> started some work there - maybe its hidden in one of my WIP branches).

I don't think we have unit tests for the xenguest library?

Thanks, Roger.