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Re: [Xen-devel] Bug on shadow page mode

>>> On 29.03.13 at 07:39, "Hao, Xudong" <xudong.hao@xxxxxxxxx> wrote:
> There is a bug with booting 3 guest with no-EPT mode, when xen handle guest 
> page fault will walk shadow guest table, fail to get l4e from the top level 
> table, then it will trigger a Fatal Page Fault and panic Xen.
> Looked at this issue and found the bug is brought by this patch 
>     changeset 26523:fd997a96d448
>     x86: debugging code for testing 16Tb support on smaller memory systems 
> I'm not much clear what's the reason of the modification(#ifdef NDEBUG) in 
> xen/arch/x86/domain_page.c of this patch?

The point is to make sure the domain page mapping code actually
gets tested. The shortcut is a performance optimization.

> But removing the macro limiting will solve the fatal page fault bug for 
> shadow page mode, can it be simply removed? or can you look at it because you 
> are very familiar with it.

While it could be removed, this would be a fix for the problem you're
seeing - you'd only later see someone else run into it on a system
with more than 5Tb.

Hence we need you to provide technical details of the crash you
observed (register and stack dump as well as call trace, plus any
details on the specific guest you're running that distinguishes it
from other guests that don't exhibit this problem).


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