Re: [XenPPC] [xenppc-unstable] [ppc] Turn on Save and Restore of VMX registers

[Jimi Xenidis <jimix@xxxxxxxxxxxxxx>]

On Jun 13, 2006, at 8:43 PM, Segher Boessenkool wrote:

> > Ok, its a bad comment :).
> > The point is that, the hypervisor cannot depend on the OSes above  
> > us to use VRSAVE at all, so we have to S&R the whole shebang.
> Ah, much clearer already.
>
> Do we really have to?  Can't we, for example, define the supervisor
> vs. hypervisor ABI wrt. VMX to be "if the hypervisor wants to use
> any VMX regs, it better S&R those itself"?  And when switching
> supervisor context, just swap-em all out.  Although perhaps this is
> just what the full code is doing, souldn't tell from the patch  
> alone :-)
The S&R of FPU and VMX (and SLB while we are at it) occurs only on  
domain switch.
We could come up with optimizations from the domain where the domain  
can assert that the FPU and VMX registers matter and in that case  
simply zero them, but that a future optimization.
-JX


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