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

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Message-ID: <20110309122046.GC16951@cr0.redhat.com>
Date:	Wed, 9 Mar 2011 20:20:46 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Mahesh Jagannath Salgaonkar <mahesh@...ux.vnet.ibm.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Anton Blanchard <anton@...ba.org>, akpm@...ux-foundation.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org
Subject: Re: [PATCH 1/2] kdump: Allow shrinking of kdump region to be
 overridden

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 <anton@...ba.org> 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.
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