Subject: Re: [PATCH 1/2] kdump: Allow shrinking of kdump region to be overridden

From: Américo Wang <[email-masked]>
Date: Wed, 9 Mar 2011 20:20:46 +0800

On Wed, Mar 09, 2011 at 12:02:06PM +0530, Mahesh Jagannath Salgaonkar wrote:
>On 08/25/2010 06:07 AM, Eric W. Biederman wrote:
>> Anton Blanchard <[email-masked]> writes:
>> 
>>> On ppc64 the crashkernel region almost always overlaps an area of firmware.
>>> This works fine except when using the sysfs interface to reduce the kdump
>>> region. If we free the firmware area we are guaranteed to crash.
>> 
>> That is ppc64 bug.  firmware should not be in the reserved region.  Any
>> random kernel like thing can be put in to that region at any valid
>> address and the fact that shrinking the region frees your firmware means
>> that using that region could also stomp your firmware (which I assume
>> would be a bad thing).
>The issue only happens while shrinking the region using sysfs interface.
>We already have checks in kexec for not to stomp over on the firmware
>overlap area while loading capture kernel. Currently we do a top-down
>allocation for the firmware region which means it sits at the top of the
>RMO, right in the middle of the crashdump region. We can not move the
>crashkernel region beyond firmware region because kernel needs its some
>of memory in RMO region.

The crashkernel region is specified via kernel cmdline, so why
not just drop a failure when it overlaps with RMO region?
Am I missing something?

Thanks.