Re: [REGRESSION] GHES firmware can't be readonly - Was: Re: [PATCH v3 3/3] arm64: acpi: Enable ACPI CCEL support

[Will Deacon <will@kernel.org>]

On Mon, Nov 24, 2025 at 05:21:00AM +0000, Suzuki K Poulose wrote:
> On 21/11/2025 21:46, Mauro Carvalho Chehab wrote:
> > Hi,
> > 
> > Em Thu, 18 Sep 2025 13:56:18 +0100
> > Suzuki K Poulose <suzuki.poulose@arm.com> escreveu:
> > 
> > > 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@arm.com>
> > > Cc: Will Deacon <will@kernel.org>
> > > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > > Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
> > > Cc: Steven Price <steven.price@arm.com>
> > > Cc: Sudeep Holla <sudeep.holla@arm.com>
> > > Cc: Gavin Shan <gshan@redhat.com>
> > > Reviewed-by: Gavin Shan <gshan@redhat.com>
> > > Tested-by: Sami Mujawar <sami.mujawar@arm.com>
> > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > > ---
> > >   arch/arm64/kernel/acpi.c | 10 ++++++++++
> > >   1 file changed, 10 insertions(+)
> > > 
> > > diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> > > index 4d529ff7ba51..b3195b3b895f 100644
> > > --- a/arch/arm64/kernel/acpi.c
> > > +++ b/arch/arm64/kernel/acpi.c
> > > @@ -357,6 +357,16 @@ void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
> > >   			 * as long as we take care not to create a writable
> > >   			 * mapping for executable code.
> > >   			 */
> > > +			fallthrough;
> > > +
> > > +		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;
> > 
> > Please revert this change.
> > 
> > Making area reserved to be used by firmware breaks some APEI
> > notification mechanisms:
> 
> Thanks for the report. Clearly, we missed this case. I am happy for this
> patch to be reverted and we can work out the handling of NVS later.

I'll revert the change shortly.

Will