[U-Boot] [PATCH 1/2] ARM: tegra: reserve unmapped RAM so EFI doesn't use it

[Heinrich Schuchardt]

On 08/29/2018 08:53 PM, Stephen Warren wrote:
> From: Stephen Warren <swarren at nvidia.com>
> 
> Tegra U-Boot ensures that board_get_usable_ram_top() never returns a value
> over 4GB, since some peripherals can't access such addresses. However, on
> systems with more than 2GB of RAM, RAM bank 1 does describe this extra
> RAM, so that Linux (or whatever OS) can use it, subject to DMA
> limitations. Since board_get_usable_ram_top() points at the top of RAM
> bank 0, the memory locations describes by RAM bank 1 are not mapped by
> U-Boot's MMU configuration, and so cannot be used for anything.
> 
> For some completely inexplicable reason, U-Boot's EFI support ignores the
> value returned by board_get_usable_ram_top(), and EFI memory allocation
> routines will return values above U-Boot's RAM top. This causes U-Boot to
> crash when it accesses that RAM, since it isn't mapped by the MMU. One
> use-case where this happens is TFTP download of a file on Jetson TX1
> (p2371-2180).
> 
> This change explicitly tells the EFI code that this extra RAM should not
> be used, thus avoiding the crash.
> 
> A previous attempt to make EFI honor board_get_usable_ram_top() was
> rejected. So, this patch will need to be replicated for any board that
> implements board_get_usable_ram_top().
> 
> Fixes: aa909462d018 ("efi_loader: efi_allocate_pages is too restrictive")
> Signed-off-by: Stephen Warren <swarren at nvidia.com>
> ---
>  arch/arm/mach-tegra/board2.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/arch/arm/mach-tegra/board2.c b/arch/arm/mach-tegra/board2.c
> index 421a71b3014d..869d5d99d2fd 100644
> --- a/arch/arm/mach-tegra/board2.c
> +++ b/arch/arm/mach-tegra/board2.c
> @@ -6,6 +6,7 @@
>  
>  #include <common.h>
>  #include <dm.h>
> +#include <efi_loader.h>
>  #include <errno.h>
>  #include <ns16550.h>
>  #include <usb.h>
> @@ -210,6 +211,19 @@ int board_early_init_f(void)
>  
>  int board_late_init(void)
>  {
> +#ifdef CONFIG_EFI_LOADER
> +	if (gd->bd->bi_dram[1].start) {
> +		/*
> +		 * Only bank 0 is below board_get_usable_ram_top(), so all of
> +		 * bank 1 is not mapped by the U-Boot MMU configuration, and so
> +		 * we must prevent EFI from using it.
> +		 */
> +		efi_add_memory_map(gd->bd->bi_dram[1].start,
> +				   gd->bd->bi_dram[1].size / 4096,

Please, do not hard code the page size here. You can use
>> EFI_PAGE_SHIFT. The constant is defined in efi.h.

> +				   EFI_RESERVED_MEMORY_TYPE, false);

The EFI spec says:

"Regions that are backed by physical hardware, but are not supposed to
be accessed by the OS, must be returned as EfiReservedMemoryType."

I assume this is not what you want. To only avoid that the U-Boot EFI
implementation uses the memory make it EFI_BOOT_SERVICES_DATA.

Best regards

Heinrich

> +	}
> +#endif
> +
>  #if defined(CONFIG_TEGRA_SUPPORT_NON_SECURE)
>  	if (tegra_cpu_is_non_secure()) {
>  		printf("CPU is in NS mode\n");
>