Re: [XenPPC] [xenppc-unstable] [POWERPC][XEN] Erratum: Must clear larx/stcx reservation on exception

[Jimi Xenidis <jimix@xxxxxxxxxxxxxx>]

On Sep 1, 2006, at 4:07 PM, Segher Boessenkool wrote:

> > [POWERPC][XEN] Erratum: Must clear larx/stcx reservation on exception
> >
> > PowerPC 970 Erratum that an "OS should execute a stcx in
> > the interrupt handler to clear the reservation."
> Where do you see this erratum?  I can't find it in any 970
> errata sheet.  Furthermore, it's not a CPU bug at all; every
> PowerPC on the planet works this way, it's part of the
> architecture.  See the "Interrupt Processing" chapter in Book III.
>
> >      stw r0, UREGS_cr(r1)            /* save CR */
> >      mfspr r0, SPRN_HSPRG1
> >      std r0, UREGS_r13(r1)           /* save R13 from HSPRG1 */
> > +
> > +    /* Blow away any reservation according to 970 errata after  
> > saving CR */
> > +    stdcx. r1, 0, r1
> I hope it's okay to blow away not only the reservation, but also
> the data that's at the memory address in GPR1, because there's
> nothing preventing this store-conditional from succeeding AFAICS
> (if the CPU happens to have a reservation there -- yeah quite
> unlikely, but is it impossible?)
Oh jeez, big DUH on me.
I wanted a store of no consequence, this ain;t it.. prolly won't hurt  
but I'll fix as soon as I can.
-JX




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