linux-kernel - Re: [RFC PATCH 3/3] x86, boot: Change the BIOS corruption checker to scan 640K

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Date:	Tue, 12 Nov 2013 05:07:03 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Olof Johansson <olof@...om.net>
Subject: Re: [RFC PATCH 3/3] x86, boot: Change the BIOS corruption checker to
 scan 640K


* H. Peter Anvin <hpa@...ux.intel.com> wrote:

> From: "H. Peter Anvin" <hpa@...ux.intel.com>
> 
> Change the BIOS corruption checker to scan 640K if enabled.  This is
> the normal amount that we otherwise would reserve with the new default
> settings; change the Kconfig help message to indicate that this is now
> intended as a diagnostic tool when one is considering enabling any
> chunk of low memory.
> 
> Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
> Cc: Olof Johansson <olof@...om.net>
> Link: http://lkml.kernel.org/r/528168CB.7070602@linux.intel.com
> ---
>  arch/x86/Kconfig        | 25 +++++++++++--------------
>  arch/x86/kernel/check.c | 10 +++++-----
>  2 files changed, 16 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 7631122..554aedd 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1384,24 +1384,21 @@ config HIGHPTE
>  config X86_CHECK_BIOS_CORRUPTION
>  	bool "Check for low memory corruption"
>  	---help---
> +	  Periodically check for memory corruption in low memory,
> +	  which is suspected to be caused by BIOS.  Even when enabled
> +	  in the configuration, it is disabled at runtime.  Enable it
> +	  by setting "memory_corruption_check=1" on the kernel command
> +	  line.  By default it reserves and scans the low 640K of
> +	  memory every 60 seconds; see the
> +	  memory_corruption_check_size and
>  	  memory_corruption_check_period parameters in
>  	  Documentation/kernel-parameters.txt to adjust this.

I agree with your patches so far, and I'd suggest we go even further: I'd 
say the config option is now a misnomer, it should probably be renamed to 
CONFIG_X86_FORCE_RESERVE_BIOS_LOW_1MB=y or so.

Btw., should we also force-reserve the remaining bits over 640K..1MB, if 
they are not marked as reserved in the memory maps, or do we already 
force-reserve them somewhere?

The CONFIG_X86_BOOTPARAM_MEMORY_CORRUPTION_CHECK=y option and the 
memory_corruption_check=1 boot option then allow the activation of the low 
memory corrupion checker - which debug facility can be used on systems 
where someone wants to live dangerously and not reserve the low 1MB of RAM 
to the firmware.

Thanks,

	Ingo
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