[U-Boot] [PATCH] efi_loader: Reserve 2 additional pages for fdt

[Leif Lindholm]

On Fri, Mar 04, 2016 at 10:19:10AM +0100, Alexander Graf wrote:
> We mark the device tree as reserved today, spanning exactly the amount
> of space it needs. If some other piece of code (like grub2) comes in and
> wants to modify the device tree to for example add a kernel command line
> though, it might assume that it has some space to do so.
> 
> So let's just reserve 2 additional pages for the device tree to play nicely.

I presume this was triggered by something you found on AArch32 grub,
booting a kernel without EFI stub?
If so, the issue will go away once I fix the AArch32 grub to use the
AArch64 loader for kernel images with the EFI stub. Could you possibly
send an email to grub-devel, or raise a ticket directly on the
savannah bugtracker if you have an account?
This fix really should go into 2.02 release.

Regardless, this seems like it provides a potential optimisation
opportunity for such agents, to use the tree in place instead of
always allocating more memory.

> Signed-off-by: Alexander Graf <agraf at suse.de>
> ---
>  cmd/bootefi.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/cmd/bootefi.c b/cmd/bootefi.c
> index de17e49..faa6978 100644
> --- a/cmd/bootefi.c
> +++ b/cmd/bootefi.c
> @@ -119,6 +119,8 @@ static unsigned long do_bootefi_exec(void *efi)
>  		fdt_end = ((ulong)working_fdt) + fdt_totalsize(working_fdt);
>  		fdt_size = (fdt_end - fdt_start) + EFI_PAGE_MASK;
>  		fdt_pages = fdt_size >> EFI_PAGE_SHIFT;
> +		/* Give a bootloader the chance to modify the device tree */
> +		fdt_pages += 2;
>  		efi_add_memory_map(fdt_start, fdt_pages,
>  				   EFI_BOOT_SERVICES_DATA, true);
>  
> -- 
> 1.8.5.6
>