Re: [Xen-devel] [PATCH 08/11] device tree, arm: supply a flat device tree to dom0

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 22/03/12 14:06, Ian Campbell wrote:
> On Mon, 2012-03-19 at 17:52 +0000, David Vrabel wrote:
>> From: David Vrabel <david.vrabel@xxxxxxxxxx>
>>
>> Build a flat device tree for dom0 based on the one supplied to Xen.
>> The following changes are made:
>>
>>   * In the /chosen node, the xen,dom0-bootargs parameter is renamed to
>>     bootargs.
>>
>>   * In all memory nodes, the reg parameters are adjusted to reflect
>>     the amount of memory dom0 can use.  The p2m is updated using this
>>     info.
>>
>> Support for passing ATAGS to dom0 is removed.
> 
> With the series applied up to and including this patch my dom0 kernel
> fails to boot with:
> [    0.000000] Linux version 3.2.0-rc5-arm-native+ (ianc@drall) (gcc version 
> 4.6.0 (GCC) ) #77 Thu Mar 22 13:58:33 GMT 2012
> [    0.000000] CPU: ARMv7 Processor [410fc0f0] revision 0 (ARMv7), cr=10c53c7d
> [    0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing 
> instruction cache
> [    0.000000] Machine: ARM Versatile Express, model: V2P-AEMv7A
> [    0.000000] bootconsole [earlycon0] enabled
> [    0.000000] Memory policy: ECC disabled, Data cache writeback
> [    0.000000] Kernel panic - not syncing: ERROR: Failed to allocate 0x1000 
> bytes below 0x0.
> [    0.000000] 
> [    0.000000] [<c000d64c>] (unwind_backtrace+0x0/0xe0) from [<c0273558>] 
> (panic+0x50/0x17c)
> [    0.000000] [<c0273558>] (panic+0x50/0x17c) from [<c032ff04>] 
> (memblock_alloc_base+0x2c/0x34)
> [    0.000000] [<c032ff04>] (memblock_alloc_base+0x2c/0x34) from [<c0329f30>] 
> (early_alloc.constprop.3+0x10/0x28)
> [    0.000000] [<c0329f30>] (early_alloc.constprop.3+0x10/0x28) from 
> [<c032a8c0>] (paging_init+0x48c/0x628)
> [    0.000000] [<c032a8c0>] (paging_init+0x48c/0x628) from [<c0328678>] 
> (setup_arch+0x508/0x7ac)
> [    0.000000] [<c0328678>] (setup_arch+0x508/0x7ac) from [<c03254dc>] 
> (start_kernel+0x6c/0x2c0)
> [    0.000000] [<c03254dc>] (start_kernel+0x6c/0x2c0) from [<80008048>] 
> (0x80008048)

This is really a bug in the memblock allocator.  You have
ARM_APPENDED_DTB enabled and you have actually appended a DTB.  The
appended DTB takes precedence over the one passed from the bootloader
and DTB in the Linux tree has 2 GiB of memory @ 2 GiB.  It looks like
the memblock allocator adds start + size, overflows and ends up with the
end of the region at 0.

You can either: a) disable ARM_APPENDED_DTB; b) not append a DTB; or c)
ensure the appended DTB's memory regions match that supplied by Xen.

David

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