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Re: [Xen-devel] d273:v3: reserved bit in page table (ec=0019)

To: "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>, "Christopher S. Aker" <caker@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] d273:v3: reserved bit in page table (ec=0019)
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Fri, 17 Jul 2009 10:30:30 +0100
Cc: xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 16.07.09 19:05 >>>
>On 16/07/2009 17:21, "Christopher S. Aker" <caker@xxxxxxxxxxxx> wrote:
>> (XEN) Pagetable walk from 00000000c0101347:
>> (XEN)  L4[0x000] = 000000067c36a027 0000000000016495
>> (XEN)  L3[0x003] = 000000067c06c027 0000000000016793
>> (XEN)  L2[0x000] = 00001f5e9d00f403 ffffffffffffffff
>                     ^^^^^^^^^^^^^^^^
>Bogus PDE -- the bottom 12 bits are potentially okay (although I don't think
>Linux uses the _PAGE_AVAIL bits) but the physical address is definitely
>bogus. Begs the question where the bogus PDE came from of course, since that
>would be the actual bug. The crash report here is the symptom when the PDE
>actually next gets used.

The low bits are definitely garbage too (unless there's a kernel component
in use that's not part of the normal 2.6.18-based kernel): L2 entries are
only ever written with _PAGE_TABLE attributes, i.e. 0x067.

It might be worth dumping out the whole L2 page, though since it's the
first entry it would also seem possible that some physical memory access
overran a page boundary. Was there any device pass-through active?


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