[PATCH v2 04/10] arm64/efi: invert UEFI memory region reservation logic

[Mark Rutland]

On Tue, Oct 28, 2014 at 04:18:37PM +0000, Ard Biesheuvel wrote:
> Instead of reserving the memory regions based on which types we know
> need to be reserved, consider only regions of the following types as
> free for general use by the OS:
> 
> EFI_LOADER_CODE
> EFI_LOADER_DATA
> EFI_BOOT_SERVICES_CODE
> EFI_BOOT_SERVICES_DATA
> EFI_CONVENTIONAL_MEMORY
> 
> Note that this also fixes a problem with the original code, which would
> misidentify a EFI_RUNTIME_SERVICES_DATA region as not reserved if it
> does not have the EFI_MEMORY_RUNTIME attribute set. However, it is
> perfectly legal for the firmware not to request a virtual mapping for
> EFI_RUNTIME_SERVICES_DATA regions that contain configuration tables, in
> which case the EFI_MEMORY_RUNTIME attribute would not be set.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> ---
>  arch/arm64/kernel/efi.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
> index 95c49ebc660d..2e829148fb36 100644
> --- a/arch/arm64/kernel/efi.c
> +++ b/arch/arm64/kernel/efi.c
> @@ -125,17 +125,17 @@ out:
>   */
>  static __init int is_reserve_region(efi_memory_desc_t *md)
>  {
> -	if (!is_normal_ram(md))
> +	switch (md->type) {
> +	case EFI_LOADER_CODE:
> +	case EFI_LOADER_DATA:
> +	case EFI_BOOT_SERVICES_CODE:
> +	case EFI_BOOT_SERVICES_DATA:
> +	case EFI_CONVENTIONAL_MEMORY:
>  		return 0;
> -
> -	if (md->attribute & EFI_MEMORY_RUNTIME)
> -		return 1;
> -
> -	if (md->type == EFI_ACPI_RECLAIM_MEMORY ||
> -	    md->type == EFI_RESERVED_TYPE)
> -		return 1;
> -
> -	return 0;
> +	default:
> +		break;
> +	}
> +	return is_normal_ram(md);

Just to check: did we figure out if UnusableMemory was allowed to have
EFI_MEMORY_WB attributes? If it isn't, this looks fine to me.

If it is, then we will need to remove that memory (rather than reserving
it) to prevent speculative accesses.

Thanks,
Mark.