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

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

>       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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