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

[Keir Fraser <keir@xxxxxxx>]

On 05/07/2012 08:50, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:

>> 
>> We're currently saving MCG_CAP, with the bank count in it
>> reflecting the host bank count, and with other bits in there also
>> matching the host's. That's what we'd like to simplify, _but_ as
>> said we're already shipping the current interface, so backward
>> compatibility will be needed anyway.
>> 
>> The main issue really was with MCi_CTL, which if not saved by
>> 4.2 wouldn't be restorable in 4.3. Now that we decided that they
>> will get fixed values anyway, simply enforcing these fixed values
>> (to not surprise the guest) would seem sufficient for 4.2. MCi_CTL2
>> are different in that afaiu setting them to 0 for a guest with no
>> saved values (i.e. 4.2, where their presence isn't being advertised,
>> since CMCI doesn't get surfaced) would be correct.
>> 
>> Jan
> 
> So Jan and Ian, do we really care migrate N -> N-1 ?
> If yes, I will save/restore MCi_CTL2, but that would involve more code change.

We categorically do not care about migration N -> N-1. N-1 -> N is the only
thing that really gets much test (N-k -> N should work by design though),
and it's the most useful one, for rolling fairly-seamless upgrades.

 -- Keir



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