Re: [PATCH] arm64: ignore DT memreserve entries when booting in UEFI mode

[Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>]

On Mon, Jul 28, 2014 at 07:03:03PM +0100, Leif Lindholm wrote:
> UEFI provides its own method for marking regions to reserve, via the
> memory map which is also used to initialise memblock. So when using the
> UEFI memory map, ignore any memreserve entries present in the DT.

It's worth noting that no-one is relying on this at present, and were
they it would imply that their UEFI implementation is broken (providing
a dodgy memory map).

So before people start doing dodgy things, let's, close that hole. If we
need a way of modifying the memory map we should come up with a more
general plan.

> Reported-by: Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>
> Signed-off-by: Leif Lindholm <leif.lindholm-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
>  arch/arm64/kernel/efi.c |    2 ++
>  arch/arm64/mm/init.c    |    4 +++-
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
> index 14db1f6..7ad17b2 100644
> --- a/arch/arm64/kernel/efi.c
> +++ b/arch/arm64/kernel/efi.c
> @@ -188,6 +188,8 @@ static __init void reserve_regions(void)
>  		if (uefi_debug)
>  			pr_cont("\n");
>  	}
> +
> +	set_bit(EFI_MEMMAP, &efi.flags);

Nothing outside of arch/x86 seems to hang off this, so using it here
looks fine.

>  }
>  
>  
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index e90c542..58dbf2e 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -32,6 +32,7 @@
>  #include <linux/of_fdt.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/dma-contiguous.h>
> +#include <linux/efi.h>
>  
>  #include <asm/sections.h>
>  #include <asm/setup.h>
> @@ -151,7 +152,8 @@ void __init arm64_memblock_init(void)
>  	memblock_reserve(__pa(swapper_pg_dir), SWAPPER_DIR_SIZE);
>  	memblock_reserve(__pa(idmap_pg_dir), IDMAP_DIR_SIZE);
>  
> -	early_init_fdt_scan_reserved_mem();
> +	if (!efi_enabled(EFI_MEMMAP))
> +		early_init_fdt_scan_reserved_mem();

And this is a false stub for !EFI, so that looks fine.

FWIW:

Reviewed-by: Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>

I wonder if we have any other flat tree uses we need to be careful of
when booting via EFI.

Thanks
Mark.

>  
>  	/* 4GB maximum for 32-bit only capable devices */
>  	if (IS_ENABLED(CONFIG_ZONE_DMA))
> -- 
> 1.7.10.4
> 
>