Re: [Xen-ia64-devel] Re: [PATCH]: ptc.ga for SMP-g

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

Hi Tristan.


+                       /* Purge tc entry.
+                          Can we do this directly ?  Well, this is just a
+                          single atomic write.  */
+                       vcpu_purge_tr_entry(&PSCBX(v,dtlb));
+                       vcpu_purge_tr_entry(&PSCBX(v,itlb));

These aren't SMP-safe because dtlb isn't read atomically. 
>From vcpu_translate()

#define vcpu_match_tr_entry(_trp,_ifa,_rid)             \
    ((_trp->p && (_trp->rid==_rid) && (_ifa >= _trp->vadr) &&   \
    (_ifa < (_trp->vadr + (1L<< _trp->ps)) - 1)))

        trp = &vcpu->arch.dtlb;
        if (/* is_data && */ vcpu_match_tr_entry(trp,address,rid)) {
                <<<<<<<<<<<<If other processor executes
                            vcpu_purge_tr_entry(&PSCBX(v,dtlb)) here,
                            then a disaster will happen >>>>>>>>>>>>>>>>
                if (vcpu->domain==dom0 && !in_tpa) *pteval = trp->page_flags;
                else *pteval = vcpu->arch.dtlb_pte;
                *itir = trp->itir;
                dtlb_translate_count++;
                return IA64_NO_FAULT;
        }

In fact it's more subtle because of memory ordering.

thanks.

On Mon, Mar 27, 2006 at 02:15:27PM +0100, Tristan Gingold wrote:
> Le Lundi 27 Mars 2006 15:07, Alex Williamson a écrit :
> > On Mon, 2006-03-27 at 13:53 +0100, Tristan Gingold wrote:
> > > Hi,
> > >
> > > this is a very simple extension of vcpu_ptc_ga to support SMP-g.
> > > The implementation could be optimized.
> >
> > Hi Tristan,
> >
> >    There's no patch attached, please resend.  Thanks,
> >
> >         Alex
> Sorry.
> Here it comes.
> 
> Tristan.
> 


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-- 
yamahata

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