On 28 July 2015 at 23:17, Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> wrote: > On Fri, 24 Jul, at 01:38:27PM, Ard Biesheuvel wrote: >> When allocating memory for the kernel image, try the AllocatePages() >> boot service to obtain memory at the preferred offset of >> 'dram_base + TEXT_OFFSET', and only revert to efi_low_alloc() if that >> fails. This is the only way to allocate at the base of DRAM if DRAM >> starts at 0x0, since efi_low_alloc() refuses to allocate at 0x0. >> >> Tested-by: Haojian Zhuang <haojian.zhuang@xxxxxxxxxx> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> >> --- >> v2: >> - reshuffle code flow to make it more logical, and have only a single >> memcpy() invocation at the end of the function >> --- >> arch/arm64/kernel/efi-stub.c | 41 ++++++++++++++++++++++++++++++++--------- >> 1 file changed, 32 insertions(+), 9 deletions(-) > > Would it be easier if we allow efi_low_alloc() to return 0x0 for some > uses? If you don't need the preference for low allocations, probably > not, but I don't want to see us working around limitations in > efi_low_alloc() instead of just fixing it. > This workaround fixes another issue as well: the arm64 kernel needs to be loaded 512 KB above a 2MB aligned boundary, and using efi_low_alloc() as we do loses (2 MB - 512 KB) at the bottom if part of that 512 KB is occupied, since efi_low_alloc() is not aware of the fact that the first 512 KB will remain unused. What would be most helpful is if efi_low_alloc() could take an offset param in addition to the alignment, i.e., alignment == 2MB and offset == 512 KB. The offset would default to 0, reverting to the original behavior. If you'd be ok with such a change, I can propose it instead, and wire it up into this function. -- Ard. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
