[U-Boot] [PATCH v2] efi_loader: Reserve unaccessible memory

[Stephen Warren]

On 11/29/18 6:11 PM, Alexander Graf wrote:
> On some systems, not all RAM may be usable within U-Boot. Maybe the
> memory maps are incomplete, maybe it's used as workaround for broken
> DMA. But whatever the reason may be, a platform can say that it does
> not wish to have its RAM accessed above a certain address by defining
> board_get_usable_ram_top().
> 
> In the efi_loader world, we ignored that hint, mostly because very few
> boards actually have real restrictions around this.
> 
> So let's honor the board's wish to not access high addresses during
> boot time. The best way to do so is by indicating the respective pages
> as "allocated by firmware". That way, Operating Systems will still
> use the pages after boot, but before boot no allocation will use them.

> diff --git a/lib/efi_loader/efi_memory.c b/lib/efi_loader/efi_memory.c

>   __weak void efi_add_known_memory(void)
>   {
> +	u64 ram_top = board_get_usable_ram_top(0) & ~EFI_PAGE_MASK;
>   	int i;
>   
> +	/* Fix for 32bit targets with ram_top at 4G */
> +	if (!ram_top)
> +		ram_top = U32_MAX;

Don't you need to &= ~EFI_PAGE_MASK after the U32_MAX assignment too? 
Perhaps just do that once:

	u64 ram_top = board_get_usable_ram_top(0);
	/* Fix for 32bit targets with ram_top at 4G */
	if (!ram_top)
		ram_top = U32_MAX;
	ram_top &=  & ~EFI_PAGE_MASK;

Otherwise,
Reviewed-by: Stephen Warren <swarren at nvidia.com>