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Re: [Xen-devel] Debian linux-image-2.6.32-4-xen-amd64 2.6.32-11 doesn't

To: Thomas Schwinge <thomas@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Debian linux-image-2.6.32-4-xen-amd64 2.6.32-11 doesn't boot with > 4 GiB; resets immediatelly, no log messages
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 20 Apr 2010 11:19:14 -0700
Cc: Ian Campbell <ijc@xxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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On 04/20/2010 04:18 AM, Thomas Schwinge wrote:
> Hello!
> On Sat, Apr 10, 2010 at 03:52:45PM -0700, Jeremy Fitzhardinge wrote:
>> On 04/10/2010 03:13 PM, Thomas Schwinge wrote:
>>>> Normally that would be OK, because it uses:
>>>>    __get_user(pfn, &machine_to_phys_mapping[mfn]);
>>>> to dereference the array.  But at this early stage, none of the kernel's
>>>> exception handlers have been set up, so this will just fault into Xen.
>>>> It would be interesting to confirm this by building your kernel with
>>>> CONFIG_DEBUG_INFO=y in the .config, and verify that the faulting
>>>> instruction is actually this line.
>>> Bingo!
>> Excellent.  Now I just need to work out how to do a proper manual limit
>> check on the mfn.  (I've always been a bit suspicious of this code,
>> because there's no guarantee that a random invalid mfn *won't* happen to
>> return the pfn we're looking for...)
> Any news already about this one?

Keir, is there a way to test the validity of an mfn before using it to
index into the m2p array?


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