[PATCH v2 0/8] Initial implementation of kdump for ARM
per.xx.fransson at stericsson.com
Mon Jul 5 06:01:06 EDT 2010
On 07/05/2010 10:28 AM, Mika Westerberg wrote:
>> I have a question regarding these patches. It seems to me that the kexec
>> will be done with the MMU left on for the ARMv7 case. Looking at the
>> code in the cpu_arm926_reset() routine in arch/arm/mm/proc-arm926.S this
>> is not the case there. Instead, the MMU is turned off and the last
>> instruction that is fetched using the virtual address mapping is a jump
>> to a physical address.
> This seems to be the case for both ARMv6 and ARMv7. I don't know
> why the MMU is not switched off there. Anyway, I've been testing
> this on ARMv7 and at least for panic kernel it works even when MMU
> is left on (didn't check but maybe the decompressor disables that
> before jumping to the kernel).
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?
>> Shouldn't this be handled as consistently as possible for the different
>> ARM sub-archs?
> Yes, I guess. I'm still wondering why this hasn't been fixed already?
Can't help you there, I'm afraid.
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