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

Alexander Graf agraf at suse.de
Wed Aug 29 21:03:10 UTC 2018



On 29.08.18 22:52, Heinrich Schuchardt wrote:
> 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.

Basically it boils down to what the memory is reserved for. For DRAM
that the OS should use, use EFI_BOOT_SERVICES_DATA. That way no U-Boot
allocations will use the memory, but Linux for example will.

If the memory however should not be used by an OS either (like a
reserved ATF region), then mark it as reserved.


Alex


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