[PATCH v3 01/11] arm64: reduce ID map to a single page

[ard.biesheuvel@linaro.org (Ard Biesheuvel)]

On 13 April 2015 at 14:53, Mark Rutland <mark.rutland@arm.com> wrote:
> Hi Ard,
>
> On Fri, Apr 10, 2015 at 02:53:45PM +0100, Ard Biesheuvel wrote:
>> Commit ea8c2e112445 ("arm64: Extend the idmap to the whole kernel
>> image") changed the early page table code so that the entire kernel
>> Image is covered by the identity map. This allows functions that
>> need to enable or disable the MMU to reside anywhere in the kernel
>> Image.
>>
>> However, this change has the unfortunate side effect that the Image
>> cannot cross a physical 512 MB alignment boundary anymore, since the
>> early page table code cannot deal with the Image crossing a /virtual/
>> 512 MB alignment boundary.
>>
>> So instead, reduce the ID map to a single page, that is populated by
>> the contents of the .idmap.text section. Only three functions reside
>> there at the moment: __enable_mmu(), cpu_resume_mmu() and cpu_reset().
>
> It would be worth mentioning in the cover letter which branch this is
> based on (arm64 for-next/core?), given the __enable_mmu + __turn_mmu_on
> folding isn't in mainline yet.
>

Ah yes. That just feels so long ago already :-)

>> If new code is introduced that needs to manipulate the MMU state, it
>> should be added to this section as well.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>
> Other than the minor nit below this looks good to me, and I've given it
> a spin on Juno with 4K and 64K pages. Assuming you can fix that up:
>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> Tested-by: Mark Rutland <mark.rutland@arm.com>
>

Thanks!

>> @@ -669,6 +669,7 @@ ENDPROC(__secondary_switched)
>>   *
>>   * other registers depend on the function called upon completion
>>   */
>> +     .section        ".idmap.text", #alloc, #execinstr
>
> We should use "ax" rather than #alloc, #execinstr to keep things
> consistent, unless there's some difference that I'm missing?
>
> I've tested the patch locally with all instances changed to "ax".
>

OK, I will change it. I have a personal preference for wordy when it
comes to things like this (try googling for ax), but as far as I know,
they are 100% equivalent.

-- 
Ard.