Re: [PATCH v3 06/10] arm64: efi: add EFI stub

From: Ard Biesheuvel
Date: Wed Feb 08 2017 - 12:41:30 EST

> On 8 Feb 2017, at 17:03, Mark Rutland <mark.rutland@xxxxxxx> wrote:
>> On Wed, Feb 08, 2017 at 10:35:02AM -0600, Timur Tabi wrote:
>> On 02/08/2017 10:29 AM, Ard Biesheuvel wrote:
>>>>>>> + status = handle_cmdline_files(sys_table, image, cmdline_ptr,
>>>>>>> + "initrd=", dram_base + SZ_512M,
>>>>>>> + (unsigned long *)&initrd_addr,
>>>>>>> + (unsigned long *)&initrd_size);
>>>>> So I know this patch is almost three years old, but why is there a
>>>>> 512M limit on the initrd size?
>>> How do you reckon this constitutes a limit?
>> handle_cmdline_files() calls efi_high_alloc() with that limit. I'm
>> still trying to understand all the details myself, but apparently
>> our firmware and initrd need to fit within the first 512MB because
>> of dram_base + SZ_512M. When we change "dram_base + SZ_512M" to
>> "~0", everything works.
> Just to check, how big is that initrd?
> I guess it's possible that there simply isn't sufficient contiguous free
> memory in that range, even if the initrd isn't that large. Can you share
> the EFI memory map dump from booting with efi=debug?
> We originally needed to restrict this to ensure that the kernel could
> map the initrd (and I think the 512M restriction specifically was
> inherited from the DTB mapping restriction). Since then, we have relaxed
> things in the kernel, and today Documentation/arm64/booting.txt says:
> If an initrd/initramfs is passed to the kernel at boot, it must
> reside entirely within a 1 GB aligned physical memory window of
> up to 32 GB in size that fully covers the kernel Image as well.
> ... so I think the EFI stub should be able to take advantage of that
> relaxation.
> Ard?

Interestingly enough, this code originates on 32-bit ARM, where the linear mapping is only 800 MB so I suspect that may have something to do with it.

I agree the stub should simply follow the rules laid out in booting.txt. I think nobody hit this because it is usually GRUB that loads the initrd not the EFI stub