linux-kernel - [PATCH v2 3/3] arm64: acpi: Enable ACPI CCEL support

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Message-ID: <20250908223519.1759020-4-suzuki.poulose@arm.com>
Date: Mon,  8 Sep 2025 23:35:19 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org,
	linux-coco@...ts.linux.dev,
	catalin.marinas@....com,
	will@...nel.org,
	gshan@...hat.com,
	aneesh.kumar@...nel.org,
	sami.mujawar@....com,
	sudeep.holla@....com,
	steven.price@....com,
	Suzuki K Poulose <suzuki.poulose@....com>
Subject: [PATCH v2 3/3] arm64: acpi: Enable ACPI CCEL support

Add support for ACPI CCEL by handling the EfiACPIMemoryNVS type memory.
As per UEFI specifications NVS memory is reserved for Firmware use even
after exiting boot services. Thus map the region as read-only.

Cc: Sami Mujawar <sami.mujawar@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
Cc: Steven Price <steven.price@....com>
Cc: Sudeep Holla <sudeep.holla@....com>
Cc: Gavin Shan <gshan@...hat.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
---
Changes since v1
 - Map NVS region as read-only, update comment to clarify that the region
   is reserved for firmware use.

---
 arch/arm64/kernel/acpi.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index 4d529ff7ba51..93b70f48a51f 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c
@@ -360,6 +360,17 @@ void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
 			prot = PAGE_KERNEL_RO;
 			break;
 
+		case EFI_ACPI_MEMORY_NVS:
+			/*
+			 * ACPI NVS marks an area reserved for use by the
+			 * firmware, even after exiting the boot service.
+			 * This may be used by the firmware for sharing dynamic
+			 * tables/data (e.g., ACPI CCEL) with the OS. Map it
+			 * as read-only.
+			 */
+			prot = PAGE_KERNEL_RO;
+			break;
+
 		case EFI_ACPI_RECLAIM_MEMORY:
 			/*
 			 * ACPI reclaim memory is used to pass firmware tables
-- 
2.43.0