Re: [PATCH 12/14] arm64: Check for selected granule support
From: Ard Biesheuvel
Date: Wed Sep 02 2015 - 05:48:47 EST
On 13 August 2015 at 19:29, Catalin Marinas <catalin.marinas@xxxxxxx> wrote:
> On Thu, Aug 13, 2015 at 03:45:07PM +0100, Suzuki K. Poulose wrote:
>> On 13/08/15 13:28, Steve Capper wrote:
>> >On 13 August 2015 at 12:34, Suzuki K. Poulose <suzuki.poulose@xxxxxxx> wrote:
>> >> __enable_mmu:
>> >>+ mrs x1, ID_AA64MMFR0_EL1
>> >>+ ubfx x2, x1, #ID_AA64MMFR0_TGran_SHIFT, 4
>> >>+ cmp x2, #ID_AA64MMFR0_TGran_ENABLED
>> >>+ b.ne __no_granule_support
>> >> ldr x5, =vectors
>> >> msr vbar_el1, x5
>> >> msr ttbr0_el1, x25 // load TTBR0
>> >>@@ -626,3 +643,8 @@ __enable_mmu:
>> >> isb
>> >> br x27
>> >> ENDPROC(__enable_mmu)
>> >>+ wfe
>> >>+ b __no_granule_support
>> >Is is possible to tell the user that the kernel has failed to boot due
>> >to the kernel granule being unsupported?
>> We don't have anything up at this time. The "looping address" is actually a clue
>> to the (expert) user. Not sure we can do something, until we get something like DEBUG_LL(?)
>> Or we should let it continue and end in a panic(?). The current situation can boot a
>> multi-cluster system with boot cluster having the Tgran support(which doesn't make a
>> strong use case though). I will try out some options and get back to you.
> If the boot CPU does not support 16KB pages, in general there isn't much
> we can do since the console printing is done after we enabled the MMU.
> Even mapping the UART address requires fixmap support and the PAGE_SIZE
> is hard-coded in the kernel image. The DT is also mapped at run-time.
> While in theory it's possible to fall back to a 4KB page size just
> enough to load the DT and figure out the early console, I suggest we
> just live with the "looping address" clue.
Couldn't we allocate some flag bits in the Image header to communicate
the page size to the bootloader?
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