Re: [Xen-devel] [PATCH] x86/AMD: Add support for AMD's OSVW feature in guests

[Boris Ostrovsky <boris.ostrovsky@xxxxxxx>]

On 01/19/12 03:10, Jan Beulich wrote:

> Btw., one more comment on the change to init_amd(): You will likely
> need to distinguish BP and AP cases here - on the BP you want to
> plainly write the values read from the MSRs to the global variables,
> but on APs (with possibly different settings) you need to work
> towards a setting of the global variables that apply to all of the
> CPUs. This is not just for the (theoretical only?) hotplug case, but
> particularly the one of a soft-offlined CPU that had its microcode
> updated already in a way affecting the OSVW bits and is
> subsequently being brought back online.

Not sure I follow you. There is no difference in how BIOS/microcode sets 
OSVW bits on AP or BP, that's based on silicon version (i.e. stepping) 
and not where that silicon is plugged in.
If a core is offlined that will presumably happen after it has already 
gone through init_amd() and therefore global versions of the registers 
already accounted for that processor's values. (The downside is that if 
the offlined processors has more bugs than the rest then everyone is 
considered as bad even though the bad processor is out of the action. 
But I think the positives of updating global variables after a cpu is 
offlined are not worth the complexity.)
> Which reminds you and me that the patch is missing integration with
> the microcode update loader (as that one may alter the OSVW bits
> iiuc).
That's a good point --- I should re-initialize the global variables 
after a patch is loaded.
Thanks.
-boris


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