linux-kernel - Re: [PATCH 2/2] acpi, apei: use appropriate pgprot

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Date:	Fri, 4 Sep 2015 12:28:20 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	"Jonathan (Zhixiong) Zhang" <zjzhang@...eaurora.org>
Cc:	Will Deacon <will.deacon@....com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org, Matt Fleming <matt.fleming@...el.com>,
	Borislav Petkov <bp@...e.de>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Catalin Marinas <Catalin.Marinas@....com>
Subject: Re: [PATCH 2/2] acpi, apei: use appropriate pgprot_t to map GHES
 memory

On Tue, 25 Aug, at 10:27:22AM, Jonathan (Zhixiong) Zhang wrote:
> From: "Jonathan (Zhixiong) Zhang" <zjzhang@...eaurora.org>
> 
> If the ACPI APEI firmware handles hardware error first (called "firmware
> first handling"), the firmware updates the GHES memory region with hardware
> error record (called "generic hardware error record"). Essentially the
> firmware writes hardware error records in the GHES memory region, triggers
> an NMI/interrupt, then the GHES driver goes off and grabs the error record
> from the GHES region.
> 
> The kernel currently maps the GHES memory region as cacheable
> (PAGE_KERNEL) for all architectures. However, on some arm64 platforms,
> there is a mismatch between how the kernel maps the GHES region
> (PAGE_KERNEL) and how the firmware maps it (EFI_MEMORY_UC, ie.
> uncacheable), leading to the possibility of the kernel GHES driver
> reading stale data from the cache when it receives the interrupt.
> 
> With stale data being read, the kernel is unaware there is new hardware
> error to be handled when there actually is; this may lead to further damage
> in various scenarios, such as error propagation caused data corruption.
> If uncorrected error (such as double bit ECC error) happened in memory
> operation and if the kernel is unaware of such event happening, errorneous
> data may be propagated to the disk.
> 
> Instead GHES memory region should be mapped with page protection type
> according to what is returned from arch_apei_get_mem_attribute().
> 
> Reviewed-by: Matt Fleming <matt@...eblueprint.co.uk>
> Acked-by: Borislav Petkov <bp@...e.de>
> Signed-off-by: Jonathan (Zhixiong) Zhang <zjzhang@...eaurora.org>
> ---
>  drivers/acpi/apei/ghes.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)

This patch message looks fine to me. Ingo?

-- 
Matt Fleming, Intel Open Source Technology Center
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