[PATCH] efi_loader: Omit memory with "no-map" when returning memory map.

[Heinrich Schuchardt]

On 8/27/21 9:55 AM, Kristian Amlie wrote:

You can use scripts/get_maintainer.pl to find the right addressees for
your patches.

> efi_reserve_memory() states that memory marked with "no-map" shall not
> be accessed by the UEFI payload. Make sure efi_get_memory_map() honors
> this.
>
> This helps the case when booting vexpress_ca9x4 under QEMU. Because
> the kernel wants to use an address in the lowest 128MiB of the range,
> but this range is reserved with "no-map", the kernel complains that it
> can not allocate the low memory it needs. In reality the actual usable
> memory starts much higher, which is reflected correctly in the memory
> map after this fix.

The 'no-map' requirement needs to be fulfilled by the kernel.

The GetMemoryMap() boot time service must comply to the UEFI specification.

The Devicetree Specification has this clarification:

"Reserved regions with the no-map property must be listed in the memory
map with type EfiReservedMemoryType. All other reserved regions must be
listed with type EfiBootServicesData."
https://devicetree-specification.readthedocs.io/en/latest/chapter3-devicenodes.html

Should the kernel calculate its internal 128 MiB requirement incorrectly
this needs be fixed in the kernel EFI stub. Does the problem exist with
kernel 5.14?

I wonder if the 128 MiB requirement of the kernel can be lifted for
32bit ARM as we already did for RISC-V. Cf.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.14&id=c79e89ecaa246c880292ba68cbe08c9c30db77e3

Cc Ard, maintainer of the kernel EFI stub.

Best regards

Heinrich

>
> Signed-off-by: Kristian Amlie <kristian.amlie at northern.tech>
> ---
>   lib/efi_loader/efi_memory.c | 14 +++++++++++++-
>   1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/lib/efi_loader/efi_memory.c b/lib/efi_loader/efi_memory.c
> index f4acbee4f9..7f8543143a 100644
> --- a/lib/efi_loader/efi_memory.c
> +++ b/lib/efi_loader/efi_memory.c
> @@ -646,8 +646,16 @@ efi_status_t efi_get_memory_map(efi_uintn_t *memory_map_size,
>
>   	provided_map_size = *memory_map_size;
>
> -	list_for_each(lhandle, &efi_mem)
> +	list_for_each(lhandle, &efi_mem) {
> +		struct efi_mem_list *lmem;
> +
> +		lmem = list_entry(lhandle, struct efi_mem_list, link);
> +
> +		if (lmem->desc.type == EFI_RESERVED_MEMORY_TYPE)
> +			continue;
> +
>   		map_entries++;
> +	}
>
>   	map_size = map_entries * sizeof(struct efi_mem_desc);
>
> @@ -672,6 +680,10 @@ efi_status_t efi_get_memory_map(efi_uintn_t *memory_map_size,
>   		struct efi_mem_list *lmem;
>
>   		lmem = list_entry(lhandle, struct efi_mem_list, link);
> +
> +		if (lmem->desc.type == EFI_RESERVED_MEMORY_TYPE)
> +			continue;
> +
>   		*memory_map = lmem->desc;
>   		memory_map--;
>   	}
>