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

From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: Will Deacon <will@kernel.org>, Christoph Hellwig <hch@lst.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Subject: [PATCH 2/3] arm64: acpi: Map EFI_MEMORY_WT memory as Normal-NC
Date: Thu,  6 May 2021 10:50:33 +0100	[thread overview]
Message-ID: <20210506095034.15246-3-will@kernel.org> (raw)
In-Reply-To: <20210506095034.15246-1-will@kernel.org>

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@kernel.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Will Deacon <will@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


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