[Xen-devel] Bug on shadow page mode

["Hao, Xudong" <xudong.hao@xxxxxxxxx>]

Hi, Jan

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?

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.

--- a/xen/arch/x86/domain_page.c        Fri Feb 08 11:06:04 2013 +0100
+++ b/xen/arch/x86/domain_page.c        Fri Mar 29 14:21:02 2013 +0800
@@ -422,10 +422,8 @@ void *map_domain_page_global(unsigned lo

     ASSERT(!in_irq() && local_irq_is_enabled());

-#ifdef NDEBUG
     if ( mfn <= PFN_DOWN(__pa(HYPERVISOR_VIRT_END - 1)) )
         return mfn_to_virt(mfn);
-#endif

     spin_lock(&globalmap_lock);


Best Regards,
Xudong Hao


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