[PATCH 2/3] arm64: acpi: Map EFI_MEMORY_WT memory as Normal-NC

[Will Deacon]

The only user we have of Normal Write-Through memory is in the ACPI code
when mapping memory regions advertised as EFI_MEMORY_WT. Since most (all?)
CPUs treat write-through as non-cacheable under the hood, don't bother
with the extra memory type here and just treat EFI_MEMORY_WT the same way
as EFI_MEMORY_WC by mapping it to the Normal-NC memory type instead.

Cc: Ard Biesheuvel <ardb at kernel.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
Cc: Christoph Hellwig <hch at lst.de>
Signed-off-by: Will Deacon <will at kernel.org>
---
 arch/arm64/kernel/acpi.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index cada0b816c8a..aca5ee2a9e64 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c
@@ -246,7 +246,7 @@ pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
 	 * types" of UEFI 2.5 section 2.3.6.1, each EFI memory type is
 	 * mapped to a corresponding MAIR attribute encoding.
 	 * The EFI memory attribute advises all possible capabilities
-	 * of a memory region. We use the most efficient capability.
+	 * of a memory region.
 	 */
 
 	u64 attr;
@@ -254,9 +254,7 @@ pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
 	attr = efi_mem_attributes(addr);
 	if (attr & EFI_MEMORY_WB)
 		return PAGE_KERNEL;
-	if (attr & EFI_MEMORY_WT)
-		return __pgprot(PROT_NORMAL_WT);
-	if (attr & EFI_MEMORY_WC)
+	if (attr & (EFI_MEMORY_WC | EFI_MEMORY_WT))
 		return __pgprot(PROT_NORMAL_NC);
 	return __pgprot(PROT_DEVICE_nGnRnE);
 }
@@ -340,9 +338,7 @@ void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
 		default:
 			if (region->attribute & EFI_MEMORY_WB)
 				prot = PAGE_KERNEL;
-			else if (region->attribute & EFI_MEMORY_WT)
-				prot = __pgprot(PROT_NORMAL_WT);
-			else if (region->attribute & EFI_MEMORY_WC)
+			else if (region->attribute & (EFI_MEMORY_WC | EFI_MEMORY_WT))
 				prot = __pgprot(PROT_NORMAL_NC);
 		}
 	}
-- 
2.31.1.607.g51e8a6a459-goog