visible memory seems wrong in kexec crash dump kernel
Scott Wood
scottwood at freescale.com
Mon Jul 29 19:10:36 EDT 2013
On 07/13/2013 01:30:50 AM, Chris Friesen wrote:
> On 07/12/2013 04:59 PM, Chris Friesen wrote:
>> On 07/12/2013 03:08 PM, Chris Friesen wrote:
>>
>>> I turned on the instrumentation in early_init_dt_scan_memory() and
>>> got
>>> the following when jumping to the capture kernel:
>>>
>>> memory scan node memory, reg size 16, data: 0 0 2 0,
>>> - 0 , 200000000
>>>
>>> That 0x200000000 matches the fact that I'm seeing 8GB of memory
>>> available in the recovery kernel.
>>>
>>> If I boot the original kernel with "crashkernel=224M at 32M", should I
>>> expect that only 224MB is marked as "linux,usable-memory" in the
>>> recovery kernel?
>>
>> I started looking at the kexec side of things, and I noticed
>> something a
>> bit odd. In most places dealing with the device tree in kexec it
>> accepts
>> either "memory" or "memory@" for the memory node name. In
>> add_usable_mem_property() in arch/ppc64/fs2dt.c it seems to only
>> accept
>> "memory@".
>>
>> Is this expected behaviour? It seems to be the same in current git
>> versions of kexec-tools.
>>
>> On my system I see "/proc/device-tree/memory".
>>
>> If I modify add_usable_mem_property() to also accept "/memory" then
>> my
>> recovery kernel boots up with
>>
>> physicalMemorySize = 0x10000000
>>
>> which is 256MB (which is still a bit odd since I specified 224MB for
>> the
>> crashkernel).
>>
>> However, it then hits the BUG() call at the end of mark_bootmem() in
>> mm/bootmem.c.
>
> One final thing and I'll stop replying to myself. :)
>
> It looks like the problem is that some board-specific freescale code
> was calling lmb_reserve() with a base address in the 4GB range. It
> seems odd that lmb_reserve() didn't throw some kind of error when the
> recovery kernel was supposed to be limited to 224MB.
>
> Rather than try and fix the bug, I turned off the (unneeded) config
> options related to the above lmb_reserve() calls and was able to
> successfully access the information I needed via /dev/oldmem.
>
> The upshot is that there seems to be a number of things that could be
> improved:
>
> 1) kexec should accept "/memory" and not just "/memory@"
> 2) lmb_reserve() should really respect the crashkernel memory limit
> 3) the freescale stuff really shouldn't assume it can map things
> wherever it feels like
What "board-specific freescale code" are you referring to?
-Scott
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