On 10 February 2017 at 00:40, Ruigrok, Richard [off-list ref] wrote:

On 2/9/2017 2:42 PM, Ard Biesheuvel wrote:

The FDT is mapped via a fixmap entry that is at least 2 MB in size and
2 MB aligned on 4 KB page size kernels.

On UEFI systems, the FDT allocation may share this 2 MB block with a
reserved region, or another memory region that we should never map,
unless we account for this in the size of the allocation (the alignment
is already 2 MB)

So instead of taking guesses at the needed space, simply allocate 2 MB
immediately. The allocation will be recorded as a EFI_LOADER_DATA, and
the kernel only memblock_reserve()'s the actual size of the FDT, so the
unused space will be released to the kernel.

Signed-off-by: Ard Biesheuvel <redacted>
---
 arch/arm64/include/asm/efi.h       |  1 +
 drivers/firmware/efi/libstub/fdt.c | 57 +++++++++-----------
 2 files changed, 25 insertions(+), 33 deletions(-)

[..]

Tested successfully on our QDT2400 system on which we were seeing a failure
to allocate memory for initrd.

Tested-by: Richard Ruigrok <redacted>

Thanks