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

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Date:	Fri, 4 Sep 2015 13:36:00 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	"Jonathan (Zhixiong) Zhang" <zjzhang@...eaurora.org>,
	Will Deacon <will.deacon@....com>,
	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


* Matt Fleming <matt@...eblueprint.co.uk> wrote:

> 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?

Looks good to me too!

Thanks,

	Ingo
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