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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: Sat, 10 Apr 2010 15:52:45 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Ian Campbell <ijc@xxxxxxxxxxxxxx>
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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...)

>     $ for ip in ffffffff814f6d88 ffffffff81433e38 ffffffff814f6d3d 
> ffffffff81433e60 ffffffff815a73ac ffffffff81433f98 ffffffff814f6f85 
> ffffffff8152b2d0 ffffffff814f95fb ffffffff814f8249 ffffffff813f3f5f 
> ffffffff813b4119 ffffffff81433f90 ffffffff811ff14f ffffffff8100e361 
> ffffffff8100e343 ffffffff813b4119 ffffffff813f3f5f ffffffff8152a7b0 
> ffffffff814f49d0 ffffffff81001000 ffffffff814f6aca ffffffff82fdb000; do echo 
> "* $ip:" && addr2line -fie debian/build/build_amd64_xen_amd64/vmlinux "$ip" 
> && gdb -q --batch --eval-command="x/i 0x$ip" --eval-command="list *0x$ip" 
> debian/build/build_amd64_xen_amd64/vmlinux; done

Oooh, nifty.


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