Re: [PATCH 08/36] AArch64: Kernel booting and initialisation

From: Christopher Covington
Date: Fri Jul 20 2012 - 10:53:45 EST

Hi Catalin,

On 07/20/2012 09:48 AM, Catalin Marinas wrote:
> On Thu, Jul 19, 2012 at 06:31:07PM +0100, Christopher Covington wrote:
>> On 07/18/2012 02:57 AM, Jon Masters wrote:
>>> On 07/06/2012 05:05 PM, Catalin Marinas wrote:
>>>> +- CPU mode
>>>> + All forms of interrupts must be masked in PSTATE.DAIF (Debug, SError,
>>>> + IRQ and FIQ).
>>>> + The CPU must be in either EL2 (RECOMMENDED) or non-secure EL1.
>> Why not secure EL1?
> Because the secure side does not have virtualisation extensions so you
> won't be able to run something like KVM.

This is another useful explanation to include, in my opinion.

>>> Even though this stuff is likely to be replaced with the result of some
>>> of the other standardization, I'd like it if you'd strongly consider
>>> removing the "or non-secure EL1". If you give an inch, someone will take
>>> a mile and build a system that enters other than in EL2. Or, something
>>> to the effect of "the highest non-secure exception level implemented"
>>> would be my preference if you don't want to specify.
>> I think it would be best to list the technical limitations, from the
>> kernel's perspective, of the unsupported exception levels and the
>> advantages of the supported exception levels here. If you want to guide
>> system builders towards EL2, I think it'd be more convincing to document
>> the relevant technical aspects (perhaps KVM needs facilities only
>> available in EL2) than just providing an unexplained requirement.
> That's not meant to be an official document for SoC designers. It just
> states the requirements from the Linux kernel perspective. But ARM is
> producing platform design documents covering hardware and firmware
> requirements and these will be made available.

I agree that the main audience for this document should be kernel and
bootloader hackers and I now think I concentrated a little too much on
how my suggestions, meant to advocate for that audience, could be seen
as aligned with Jon's comment.

Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
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