[RFC] efi: Add ACPI_MEMORY_NVS into the linear map

[Boqun Feng]

(Cc the correct arm mailing list)

On Thu, Feb 15, 2024 at 02:51:06PM -0800, Boqun Feng wrote:
> Currently ACPI_MEMORY_NVS is omitted from the linear map, which causes
> a trouble with the following firmware memory region setup:
> 
> 	[..] efi:   0x0000dfd62000-0x0000dfd83fff [ACPI Reclaim|...]
> 	[..] efi:   0x0000dfd84000-0x0000dfd87fff [ACPI Mem NVS|...]
> 
> , on ARM64 with 64k page size, the whole 0x0000dfd80000-0x0000dfd8ffff
> range will be omitted from the the linear map due to 64k round-up. And
> a page fault happens when trying to access the ACPI_RECLAIM_MEMORY:
> 
> 	[...] Unable to handle kernel paging request at virtual address ffff0000dfd80000
> 
> To fix this, add ACPI_MEMORY_NVS into the linear map.
> 
> Signed-off-by: Boqun Feng <boqun.feng at gmail.com>
> Cc: stable at vger.kernel.org # 5.15+
> ---
> We hit this in an ARM64 Hyper-V VM when using 64k page size, although
> this issue may also be fixed if the efi memory regions are all 64k
> aligned, but I don't find this memory region setup is invalid per UEFI
> spec, also I don't find that spec disallows ACPI_MEMORY_NVS to be mapped
> in the OS linear map, but if there is any better way or I'm reading the
> spec incorrectly, please let me know.
> 
> It's Cced stable since 5.15 because that's when Hyper-V ARM64 support is
> added, and Hyper-V is the only one that hits the problem so far.
> 
>  drivers/firmware/efi/efi-init.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firmware/efi/efi-init.c b/drivers/firmware/efi/efi-init.c
> index a00e07b853f2..9a1b9bc66d50 100644
> --- a/drivers/firmware/efi/efi-init.c
> +++ b/drivers/firmware/efi/efi-init.c
> @@ -139,6 +139,7 @@ static __init int is_usable_memory(efi_memory_desc_t *md)
>  	case EFI_LOADER_CODE:
>  	case EFI_LOADER_DATA:
>  	case EFI_ACPI_RECLAIM_MEMORY:
> +	case EFI_ACPI_MEMORY_NVS:
>  	case EFI_BOOT_SERVICES_CODE:
>  	case EFI_BOOT_SERVICES_DATA:
>  	case EFI_CONVENTIONAL_MEMORY:
> @@ -202,8 +203,12 @@ static __init void reserve_regions(void)
>  			if (!is_usable_memory(md))
>  				memblock_mark_nomap(paddr, size);
>  
> -			/* keep ACPI reclaim memory intact for kexec etc. */
> -			if (md->type == EFI_ACPI_RECLAIM_MEMORY)
> +			/*
> +			 * keep ACPI reclaim and NVS memory and intact for kexec
> +			 * etc.
> +			 */
> +			if (md->type == EFI_ACPI_RECLAIM_MEMORY ||
> +			    md->type == EFI_ACPI_MEMORY_NVS)
>  				memblock_reserve(paddr, size);
>  		}
>  	}
> -- 
> 2.43.0
>