Re: [PATCH v2 3/6] libxl: introduce MSR data in libxl_cpuid_policy

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Mon, Jul 17, 2023 at 04:36:11PM +0200, Roger Pau Monné wrote:
> On Wed, Jul 12, 2023 at 05:39:01PM +0100, Anthony PERARD wrote:
> > On Tue, Jul 11, 2023 at 11:22:27AM +0200, Roger Pau Monne wrote:
> > > Add a new array field to libxl_cpuid_policy in order to store the MSR
> > > policies.
> > > 
> > > Note that libxl_cpuid_policy_list_{copy,length,parse_json,gen_json}
> > > are not adjusted to deal with the new MSR array now part of
> > > libxl_cpuid_policy_list.
> > 
> > Why? Isn't this going to be an issue? Or maybe that going to be dealt
> > with in a future patch?
> 
> I'm unsure what's the point of those?  The CPUID/MSR data is passed as
> a migration stream record from the hypervisor, so I don't see much
> point into converting it into json.  It also seems quite complex, and
> can't likely we done without breaking (or adjusting) the current
> format.

I think this data is used when the machine reboots. I've only try to
edit the file "/var/lib/xen/userdata-d.*" and it change which cpu flags
where available in the machine after a reboot. You could maybe confirm
that when you change an msr value, it is actually conserved across
reboot.

> My plan was to leave this unimplemented and if someone is in
> interested in having the data in json they can as well implement it.
> 
> Would you be OK if I add a note to the commit message that
> implementing json marshalling is left to implement for interested
> parties?

My guess is, we will have to think of something and add the msr into
json, even if it's done in a separate patch.

Cheers,

-- 
Anthony PERARD