Re: [PATCH v2 1/2] efi: arm-stub: Correct FDT and initrd allocation rules for arm64

Ard Biesheuvel
2017-02-10T14:58:02Z

On 10 February 2017 at 10:05, Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org> wrote:
> On Fri, Feb 10, 2017 at 06:38:11AM +0000, Ard Biesheuvel wrote:
>> > On 10 Feb 2017, at 00:42, Ruigrok, Richard <rruigrok-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org> wrote:
>> >> On 2/9/2017 2:42 PM, Ard Biesheuvel wrote:
>
>> >> diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
>> >> index 0b6b1633017f..342e90d6d204 100644
>> >> --- a/arch/arm64/include/asm/efi.h
>> >> +++ b/arch/arm64/include/asm/efi.h
>> >> @@ -46,7 +46,23 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md);
>> >> * 2MiB so we know it won't cross a 2MiB boundary.
>> >> */
>> >> #define EFI_FDT_ALIGN SZ_2M /* used by allocate_new_fdt_and_exit_boot() */
>> >> -#define MAX_FDT_OFFSET SZ_512M
>> >> +
>> >> +/* on arm64, the FDT may be located anywhere in system RAM */
>> >> +static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base)
>> >> +{
>> >> + return ULONG_MAX;
>> >> +}
>> >> +
>> >> +/*
>> >> + * On arm64, we have to ensure that the initrd ends up in the linear region,
>> >> + * which is a 1 GB aligned region of size '1UL << (VA_BITS - 1)' that is
>> >> + * guaranteed to cover the kernel Image.
>> >> + */
>> >> +static inline unsigned long efi_get_max_initrd_addr(unsigned long dram_base,
>> >> + unsigned long image_addr)
>> >> +{
>> >> + return (image_addr & ~(SZ_1G - 1UL)) + (1UL << (VA_BITS - 1));
>> >> +}
>> >>
>> > Please update booting.txt which specifies a window of 32G for ARM64
>> >
>>
>> No. The efi stub is built into the kernel, so there we can be lax
>> about these things.
>
> Sure.
>
> Given this is a source of confusion, can we drop a comment here as to
> how this is deliberate? e.g.
>
> /*
> * On arm64, we have to ensure that the initrd ends up in the linear region,
> * which is a 1 GB aligned region of size '1UL << (VA_BITS - 1)' that is
> * guaranteed to cover the kernel Image.
> *
> * Since the EFI stub is part of the kernel Image, we can relax than the
> * usual requirements in Documentation/arm64/booting.txt, which still
> * apply to other bootloaders, and are required for some kernel
> * configurations.
> */
>

Absolutely