[PATCH] efi: arm64: treat regions with WT/WC set but WB cleared as memory

[Ard Biesheuvel]

Currently, memory regions are only recorded in the memblock memory table
if they have the EFI_MEMORY_WB memory type attribute set. In case the
region is of a reserved type, it is also marked as MEMBLOCK_NOMAP, which
will leave it out of the linear mapping.

However, memory regions may legally have the EFI_MEMORY_WT or EFI_MEMORY_WC
attributes set, and the EFI_MEMORY_WB cleared, in which case the region in
question is obviously backed by normal memory, but is not recorded in the
memblock memory table at all. Since it would be useful to be able to
identify any UEFI reported memory region using memblock_is_memory(), it
makes sense to add all memory to the memblock memory table, and simply mark
it as MEMBLOCK_NOMAP if it lacks the EFI_MEMORY_WB attribute.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---

Note that this will also result in regions with EFI_MEMORY_WB cleared to
be listed in /proc/iomem as 'System RAM', which may be incorrect. However,
we already display this incorrect behavior for runtime services code/data
regions, so this should be fixed in a separate patch, of which an example
has been proposed here:
https://www.spinics.net/lists/arm-kernel/msg525369.html

 drivers/firmware/efi/arm-init.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efi/arm-init.c b/drivers/firmware/efi/arm-init.c
index c49d50e68aee..678672d332f8 100644
--- a/drivers/firmware/efi/arm-init.c
+++ b/drivers/firmware/efi/arm-init.c
@@ -28,7 +28,7 @@ u64 efi_system_table;
 
 static int __init is_normal_ram(efi_memory_desc_t *md)
 {
-	if (md->attribute & EFI_MEMORY_WB)
+	if (md->attribute & (EFI_MEMORY_WB|EFI_MEMORY_WT|EFI_MEMORY_WC))
 		return 1;
 	return 0;
 }
@@ -163,7 +163,13 @@ static __init int is_reserve_region(efi_memory_desc_t *md)
 	case EFI_BOOT_SERVICES_DATA:
 	case EFI_CONVENTIONAL_MEMORY:
 	case EFI_PERSISTENT_MEMORY:
-		return 0;
+		/*
+		 * According to the spec, these regions are no longer reserved
+		 * after calling ExitBootServices(). However, we can only use
+		 * them as System RAM if they can be mapped writeback cacheable.
+		 * Otherwise, treat them as reserved.
+		 */
+		return (md->type & EFI_MEMORY_WB) == 0;
 	default:
 		break;
 	}
-- 
2.7.4