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

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Message-ID: <aHZeCKNyDeZEsuCt@willie-the-truck>
Date: Tue, 15 Jul 2025 14:56:24 +0100
From: Will Deacon <will@...nel.org>
To: Suzuki K Poulose <suzuki.poulose@....com>
Cc: linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
	sami.mujawar@....com, aneesh.kumar@...nel.org, steven.price@....com,
	linux-kernel@...r.kernel.org, sudeep.holla@....com
Subject: Re: [PATCH 3/3] arm64: acpi: Enable ACPI CCEL support

On Fri, Jun 13, 2025 at 12:11:53PM +0100, Suzuki K Poulose wrote:
> ACPI CCEL memory area is reported as Non-Volatile storage area. Map it as
> PAGE_KERNEL.

It would be helpful to have a citation for that. I've tried digging it
out of the ACPI spec, but that pointed me to the Intel TDX site and I
got lost in whitepapers :/

> 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>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  arch/arm64/kernel/acpi.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> index b9a66fc146c9..f52439d411a0 100644
> --- a/arch/arm64/kernel/acpi.c
> +++ b/arch/arm64/kernel/acpi.c
> @@ -356,6 +356,11 @@ void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
>  			prot = PAGE_KERNEL_RO;
>  			break;
>  
> +		case EFI_ACPI_MEMORY_NVS:
> +			/* Non-volatile storage, required for CCEL */
> +			prot = PAGE_KERNEL;

By "storage" you just mean memory, right?

Will