linux-kernel - Re: [Patch V1 2/3] x86, mce: Add infrastructure required to support LMCE

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Date:	Fri, 29 May 2015 19:44:39 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Ashok Raj <ashok.raj@...el.com>
Cc:	linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
	Borislav Petkov <bp@...e.de>, Tony Luck <tony.luck@...el.com>
Subject: Re: [Patch V1 2/3] x86, mce: Add infrastructure required to support
 LMCE

On Fri, May 29, 2015 at 09:28:01AM -0700, Ashok Raj wrote:
> Initialization and handling for LMCE
> - boot time option to disable LMCE for that boot instance
> - Check for capability via IA32_MCG_CAP
> - provide ability to enable/disable LMCE on demand.
> 
> See http://www.intel.com/sdm Volume 3 System Programming Guide, Chapter 15
> for more information on MSR's and documentation on Local MCE.
> 
> Signed-off-by: Ashok Raj <ashok.raj@...el.com>
> ---
>  Documentation/x86/x86_64/boot-options.txt |  3 ++
>  arch/x86/include/asm/mce.h                |  5 +++
>  arch/x86/kernel/cpu/mcheck/mce.c          |  3 ++
>  arch/x86/kernel/cpu/mcheck/mce_intel.c    | 75 +++++++++++++++++++++++++++++++
>  4 files changed, 86 insertions(+)

...

> +static bool lmce_supported(void)
> +{
> +	u64 cap, feature_ctl;
> +	bool lmce_bios_support, retval;
> +
> +	if (mca_cfg.lmce_disabled)
> +		return false;
> +
> +	rdmsrl(MSR_IA32_MCG_CAP, cap);
> +	rdmsrl(MSR_IA32_FEATURE_CONTROL, feature_ctl);

One more thing: You should check MCG_LMCE_P *first* and only read
MSR_IA32_FEATURE_CONTROL if MCG_LMCE_P is set - otherwise this'll start
blowing up on older machines which don't sport that new MSR and on kvm.

> +	/*
> +	 * BIOS should indicate support for LMCE by setting
> +	 * bit20 in IA32_FEATURE_CONTROL. without which touching
> +	 * MCG_EXT_CTL will generate #GP fault.
> +	 */
> +	lmce_bios_support = ((feature_ctl & (FEATURE_CONTROL_LMCE_BITS)) ==
> +			(FEATURE_CONTROL_LMCE_BITS));
> +
> +	/*
> +	 * MCG_CAP should indicate both MCG_SER_P and MCG_LMCE_P
> +	 */

Also, why do we need to look at MCG_SER_P for LMCE?

Btw, we do that already in __mcheck_cpu_cap_init() so you could check
mca_cfg.ser here instead.

> +	cap = ((cap & MCG_CAP_LMCE_BITS) == (MCG_CAP_LMCE_BITS));
> +	retval = (cap && lmce_bios_support);

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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