Re: [Xen-devel] [PATCH 2/2] x86/vMCE: save/restore MCA capabilities

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.03.12 at 09:29, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
> Jan Beulich wrote:
>>>>> On 05.03.12 at 21:19, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
>>> Another question is, why in the patch mcg_cap defined as per vcpu
>>> while others (mcg_ctl/ mcg_status/ mci_ctl) defined as per domain?
>>> Semantically it looks some weird anyway.
>> 
>> That question goes back to you (as a company), who wrote the
>> original code: Why were these made per-domain in the first place
>> when they're really per-vCPU? All I did here is make per-vCPU
>> what I needed to touch anyway for save/restore (in order to not
>> carry over the same mistake into the save/restore definitions and
>> logic).
>> 
>> Jan
> 
> Per my understanding, the original design may think that per vcpu mca msr is 
> not necessary: vcpu are not 1:1 w/ pcpu, and multi-copies of same error info 
> (if per vcpu) is pointless, so it designed as per domain, as long as it 
> successfully emulated mca msr for guest.

But as with anything that is being done differently when virtualized,
this may come back and bite us when a need for per-vCPU treatment
is needed. As long as this was purely internal to a particular
hypervisor instance, this was just poor design needing a potentially
larger patch to overcome, but with the involvement of save/restore
it needs to be done properly to allow forward compatibility.

But we're getting all the farther away from the actual question: Do
we need to provide for saving/restoring of any of the _CTL
registers?

Jan


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