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Re: [Xen-devel] [PATCH] xen: arm: setup sane EL1 state while building domain 0.

On 03/18/2014 05:41 PM, Ian Campbell wrote:
> On Tue, 2014-03-18 at 11:22 +0800, Fu Wei wrote:
>> On 03/17/2014 11:31 PM, Ian Campbell wrote:
>>> The address translation functions used while building dom0 rely on certain 
>>> EL1
>>> state being configured. In particular they are subject to the behaviour of
>>> SCTLR_EL1.M (stage 1 MMU enabled).
>>> The Xen (and Linux) boot protocol require that the kernel be entered with 
>>> the
>>> MMU disabled but they don't say anything explicitly about exception levels
>>> other than the one which is active when entering the kernels. Arguably the
>>> protocol could be said to apply to all exception levels but in any case we
>>> should cope with this and setup the EL1 state as necessary.
>>> Fu Wei discovered this when booting Xen from grub.efi over UEFI, it's not
>>> clear whether grub or UEFI is responsible for leaving stage 1 MMU enabled.
>>> Reported-by: Fu Wei <fu.wei@xxxxxxxxxx>
>>> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
>>> Cc: Fu Wei <fu.wei@xxxxxxxxxx>
>>> ---
>>> Fu Wei, can I add your Tested-by here?
>> Yes, Thanks!
>> I have tested this with my GRUB binary, it works fine.
> Great. Thanks. It looks like we might rework the approach, if so I'll CC
> you on that as well (or Julien will).
> Are you also going to change grub to leave EL1 in a known good state?

I don't think it's the work of grub to modify EL1 register.
if the booting.txt(xen or linux) doesn't mention about EL1, I think the 
kernel(xen or linux) should take care of these EL1 registers. 
And at the time, xen has booted up, it can modify EL1 registers.

Do you agree?  :-)

> Ian.

Best regards,

Fu Wei
LAVA Engineer From Red Hat
Linaro.org | Open source software for ARM SoCs
Ph: +86 186 2020 4684 (mobile)
IRC: fuwei
Skype: tekkamanninja
Room 1512, Regus One Corporate Avenue,Level 15,
One Corporate Avenue,222 Hubin Road,Huangpu District,
Shanghai,China 200021 

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