RE: [Xen-ia64-devel] RE: [PATCH] Patch to make latest hgmulti-domainback to work

["Magenheimer, Dan (HP Labs Fort Collins)" <dan.magenheimer@xxxxxx>]

I meant to add... however, without this change domain0
is unusable.  Since I can't test any other patches (e.g.
Anthony's double mapping patch) without it, I am going
to apply it to the tree temporarily while we figure
out what is going on. 

> -----Original Message-----
> From: xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf 
> Of Magenheimer, Dan (HP Labs Fort Collins)
> Sent: Thursday, September 08, 2005 6:50 AM
> To: Tian, Kevin; Byrne, John (HP Labs)
> Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> Subject: RE: [Xen-ia64-devel] RE: [PATCH] Patch to make 
> latest hgmulti-domainback to work
> 
> >     Could you elaborate more how your latest patch works 
> > differently and fix the potential issue?
> > 
> > -               *pteval = vcpu->arch.dtlb_pte;
> > +               if (vcpu->domain==dom0 && !in_tpa) *pteval = 
> > trp->page_flags;
> > +               else *pteval = vcpu->arch.dtlb_pte;
> > +               printf("DTLB MATCH... NEW, DOM%s, %s\n", 
> > vcpu->domain==dom0?
> > +                       "0":"U", 
> > in_tpa?"vcpu_tpa":"ia64_do_page_fault");
> > 
> >     The new limitation seems only for dom0, while dom0 has 
> > exactly same guest physical address as machine address. Based 
> > upon this assumption, trp->page_flags actually equals to 
> > guest pte (vcpu->arch.dtlb_pte)? So I'm not sure about the 
> > trick here behind.
> 
> I don't understand myself why the fix works, which is why
> I didn't propose it as a "final" patch.  In tracking down
> the crash, I added printfs to see when it happened and
> found that it only occurred in domain0 when vcpu_translate
> was called from vcpu_tpa and so tried the above workaround
> and it eliminated the crash.
> 
> I didn't have time at that point to study why the fix worked,
> so just posted the workaround in case others were having
> problems with the crash.
> 
> I agree that the fix doesn't seem like it should work.  There's
> something else strange going on (cue music from Twilight
> Zone here).
> 
> Dan
> 
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