On Fri, Feb 15, 2002 at 10:59:09AM +0100, Kevin D. Kissell wrote:
> > > > > I have been chasing a FPU register corruption problem on a SMP box.
> > > > > The
> > > > > curruption seems to be caused by FPU emulator code. Is that code SMP
> > > > > safe?
> > > > > If not, what are the volunerable spots?
> > > >
> > > > In theory the fp emulation code should be MP safe as the full emulation
> > > > is only accessing it's context in the fp register set of struct
> > > > task_struct. The 32-bit kernel's fp register switching is entirely
> > > > broken
> > > > (read: close to non-existant). Lots of brownie points for somebody to
> > > > backport that from the 64-bit kernel to the 32-bit kernel and forward
> > > > port all the FPU emu bits to the 64-bit kernel ...
> > > >
> > >
> > > Brownie sounds good. :-) So what is the "fp register switching" you are
> > > referring to? There is set of code related to lazy fpu context switch,
> > > which seems to be working fine now.
> > >
> >
> > Hmm, I see. The lazy fpu context switch code is not SMP safe.
> > I see fishy things like "last_task_used_math" etc...
>
> What, you mean "last_task_used_math" isn't allocated in a
> processor-specific page of kseg3??? ;-)
>
You must be talking about another OS, right? :-) I don't think
Linux has processor-specific page, although this sounds like
a good idea to explore.
Jun
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