Re: [PATCH 2 of 2] vpmu: Add a vpmu cpuid function

[Keir Fraser <keir.xen@gmail.com>]

On 20/01/2012 12:45, "Ian Campbell" <Ian.Campbell@citrix.com> wrote:

>>> It's obviously an option of fairly narrow interest. If someone tries to
>>> enable the per-domain option on a CPU which has problems, you can fail the
>>> domain creation, or print a warning in the hypervisor log, or whatever. Any
>>> sensible option in that respect is fine by me!
>> 
>> What is the best solution for this?
>> A domain specific configuration option is needed (vpmu?) which is usable in
>> libxc/xc_cpuid_x86.c to select/deselect special vpmu bits in the cpuid
>> command.
>> Can you point me to an proper example?
> 
> Can't this already be done via the cpuid domain option given the correct
> runes? Maybe with an addition to the table in libxl_cpuid_parse_config?

Yes that's probably the way to do it. If the resulting required
configuration runes are too cryptic or vendor-specific, it may make sense to
have the libxl cpuid logic consume a 'vpmu' option which it then turns into
a set of lower-level cpuid settings to eventually pass down to the code in
libxc/xc_cpuid.

It's a trifle messy I will admit. Arguably the 'default policy' bits of
xc_cpuid_x86.c would better belong in libxl these days, where we would have
better access to a domain's configuration state. As it is, we may end up
with a spread of default policy across Xen (for dom0), libxc, and libxl.

 -- Keir