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

["Luck, Tony" <tony.luck@xxxxxxxxx>]

> Yes, it's vMCE specific issue, and only under the case when migrate from 
> platform
> A w/ bigger bank number to platform B w/ smaller bank number. Under this case,
> it would block migration from 3.x -> 4.0 -> 4.1 -> 4.2.

Linux (and probably every other OS) will only look to see how many banks there
are once at boot time. From that point on it will scan as many banks as it was 
told
existed for the rest of eternity. So it really doesn't matter what value you 
present
in MCG_CAP after a  migration - the OS will never look at it any way. The 
important
thing is what you do when the OS does:
        for (i = 0; i < banks; i++) {
                status = mce_rdmsrl(MSR_IA32_MCx_STATUS(i));
                ...
        }
because you'd better give it something reasonable for each bank that it was
told existed.

Also if you are going to present a machine check to the guest, then you need to
fill in the data for some bank that it knows about (i.e. i < banks ... and 
possibly
i != 0 for certain CPUIDs).

-Tony

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