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

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Message-ID: <aHZsgzNYwfCljX-G@willie-the-truck>
Date: Tue, 15 Jul 2025 15:58:11 +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 Tue, Jul 15, 2025 at 03:38:41PM +0100, Suzuki K Poulose wrote:
> On 15/07/2025 14:56, Will Deacon wrote:
> > 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 :/
> > 
> 
> https://uefi.org/specs/ACPI/6.5/05_ACPI_Software_Programming_Model.html#cc-event-log-acpi-table

Thanks, but I still can't spot where it specifies the memory attributes.
I think we should be able to refer to that as justification for ignoring
the attributes specified by EFI.

> > > 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?
> 
> Yep, it is just memory. I will drop the "NV storage" and simply mention,
> CCEL.

Thanks. Also, why don't we check against memblock_is_map_memory() for
this, like we do for all the other types apart from
EFI_RUNTIME_SERVICES_CODE?

Will