[PATCH 06/12] ARM: kexec: advertise location of bootable RAM

[Pratyush Anand]

On Sat, Apr 30, 2016 at 1:50 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Sat, Apr 30, 2016 at 08:57:34AM +0530, Pratyush Anand wrote:
>> On Fri, Apr 29, 2016 at 11:30 PM, Russell King - ARM Linux
>> <linux at arm.linux.org.uk> wrote:
>> > On Fri, Apr 29, 2016 at 08:26:00PM +0530, Pratyush Anand wrote:
>> >> Hi Russell,
>> >>
>> >> On Thu, Apr 28, 2016 at 2:58 PM, Russell King
>> >> <rmk+kernel at arm.linux.org.uk> wrote:
>> >> > Advertise the location of bootable RAM to kexec-tools.  kexec needs to
>> >> > know where it can place the kernel in RAM, and so be executable when
>> >> > the system needs to jump into it.
>> >> >
>> >> > Advertise these areas in /proc/iomem with a "System RAM (boot alias)"
>> >> > tag.
>> >> >
>> >> > Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
>> >>
>> >> Can you please also share git tree path of corresponding kexec-tools changes?
>> >>
>> >> Could it be a better idea (if things in user space become simpler)
>> >> that in stead of patch 5 and 6, we pass arch_phys_to_idmap_offset to
>> >> user space, and then user space manipulates existing "Crash kernel"
>> >> and "System RAM" resources.
>> >
>> > Given that it's only _one_ platform right now, I don't think that
>> > additional complexity is worth it.  It means that we have to invent
>>
>> Probably, I could not communicate it well.  I was not trying  to have
>> *additional* complexity. Wanted to see if things could be simpler
>> rather. So this is what my understanding was:
>> -- We create one patch to pass arch_phys_to_idmap_offset to user space
>> (say in /sys/kernel/bootmem_idmap_offset)
>> -- We do not use patch 5,6,11 and 12 of this series. Probably few more
>> content of the series will go away.
>
> Patches 11 and 12 don't go away with what you're suggesting.  Patches
> 11 and 12 are necessary to allow the boot-view addresses to be passed
> into the kernel through kexec, and to allow kexec to find appropriate
> memory resources.

But once we would have manipulated "start" and "end" of "Crash Kernel"
and "System RAM" resources in user space using
/sys/kernel/bootmem_idmap_offset , then kernel through kexec system
call would have already receive boot-view addresses, no?

~Pratyush