From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Mon, 5 Jul 2010 11:18:52 +0100
Subject: [PATCH v2 0/8] Initial implementation of kdump for ARM
In-Reply-To: <4C31AD62.6070805@stericsson.com>
References: <20100611063605.GB11156@esdhcp04058.research.nokia.com>
	<4C2DE024.8060308@stericsson.com>
	<20100705082835.GA32178@gw.healthdatacare.com>
	<4C31AD62.6070805@stericsson.com>
Message-ID: <20100705101852.GA19338@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Mon, Jul 05, 2010 at 12:01:06PM +0200, Per Fransson wrote:
> In machine_kexec an identity mapping is set up for the user space part  
> of the virtual address space, through a call to setup_mm_for_reboot(). I  
> believe this mapping is only necessary because the MMU is kept on and if  
> the kexec is done to facilitate the collection of a dump it would be  
> nice if a large part of the page table for the crashing context has not  
> been corrupted. Don't you agree?

No.  The identity mapping is there so that we can safely disable the MMU
and jump to the intended address.

There is an implementation defined delay between writing the control
register and the point in the instruction stream that the effect of that
write is seen.

The missing MMU disable for AMRv6 and ARMv7 is an oversight which needs
to be resolved.