Re: [Xen-devel] [PATCH] Xen/MCE: adjust for future new vMCE model

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-07-05 at 07:44 +0100, Ian Campbell wrote:
> On Thu, 2012-07-05 at 07:39 +0100, Jan Beulich wrote:
> > >>> On 05.07.12 at 05:03, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
> > > Jan Beulich wrote:
> > >> Also I seem to recall that there was going to be a need to
> > >> save/restore MCi_CTL2, but there's nothing being done in that
> > >> direction.
> > > 
> > > Yes, but that would be done at new vMCE.
> > > Current vMCE didn't enable MCG_CMCI_P, and MCi_CTL2 are not used, so we 
> > > don't save/restore MCi_CTL2 at this version.
> > 
> > But _that_ is the major save/restore related issue to be
> > addressed, at least if backward migration (4.2 -> 4.1) is also
> > to be working reasonably. If such compatibility is entirely
> > unneeded, then I agree that it likely doesn't need any
> > consideration at this point.
> 
> We don't generally worry about N->N-1 migration, just N->N+1.

If there's nothing to save in 4.2 (and therefore to restore in 4.3) what
is it we are giving a freeze exception to again?

If there's no save/restore can you even migrate a guest with vMCE
enabled at all?

(these aren't rhetorical questions, I have absolutely no idea how this
stuff works ;-))

Ian.



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