RE: [Xen-ia64-devel] PATCH: [resent] cleanup + fph handling

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Tristan Gingold
>Sent: 2006年4月24日 16:40
>Hi,
>
>
>this patch moves switch_to macro from xensystem.h and put its body
>directly in
>context_switch.  FP saved and restore is slighly optimized: fph is *still*
>enabled and not anymore disabled.
>
>Misc cleanup.
>
>Note: not enabling fph before saving fph in context switch does not work.
>I
>will look on this issue.  However,  I think it is worth adding this patch.
>

If you failed at the first context switch, the possible cause is in head.S 
where psr.dfh is initialized as disabled for idle domain. Then the first 
time when you switch from idle to domain0, disabled fp fault occurs 
unless you explicitly enable psr.dfh like in your patch. This is one place
where psr value doesn't get from hardware exception.

Linux is immune because it always touches fph only for the one 
owning the that high area.

Thanks,
Kevin

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