linux-kernel - Re: [PATCH] x86: mce: Honour bios-set CMCI threshold

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Date:	Thu, 23 Aug 2012 17:26:09 +0530
From:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:	Borislav Petkov <bp@...64.org>
CC:	tony.luck@...el.com, andi@...stfloor.org,
	gong.chen@...ux.intel.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
	linux-edac@...r.kernel.org, ananth@...ibm.com,
	Chris McDermott <lcm@...ibm.com>, masbock@...ux.vnet.ibm.com
Subject: Re: [PATCH] x86: mce: Honour bios-set CMCI threshold

On 08/22/2012 06:16 PM, Borislav Petkov wrote:
> On Wed, Aug 22, 2012 at 06:00:54PM +0530, Naveen N. Rao wrote:
>> The ACPI spec doesn't provide for a way for the bios to pass down
>> recommended thresholds to the OS on a _per-bank_ basis. This patch adds
>> a new boot option, which if passed, allows bios to initialize the CMCI
>> threshold. In such a case, we simply skip programming any threshold
>> value.
>>
>> As fail-safe, we initialize threshold to 1 if some banks have not been
>> initialized by the bios and warn the user.
>>
>> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
>> ---
>>   Documentation/x86/x86_64/boot-options.txt |    5 ++++
>>   arch/x86/include/asm/mce.h                |    1 +
>>   arch/x86/kernel/cpu/mcheck/mce.c          |    4 +++
>>   arch/x86/kernel/cpu/mcheck/mce_intel.c    |   39 +++++++++++++++++++++++++++--
>>   4 files changed, 46 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/x86/x86_64/boot-options.txt b/Documentation/x86/x86_64/boot-options.txt
>> index c54b4f5..ec92540 100644
>> --- a/Documentation/x86/x86_64/boot-options.txt
>> +++ b/Documentation/x86/x86_64/boot-options.txt
>> @@ -50,6 +50,11 @@ Machine check
>>   		monarchtimeout:
>>   		Sets the time in us to wait for other CPUs on machine checks. 0
>>   		to disable.
>> +   mce=bios_cmci_threshold
>> +		Don't overwrite the bios-set CMCI threshold. This boot option
>> +		prevents Linux from overwriting the CMCI threshold set by the
>> +		bios. Without this option, Linux always sets the CMCI
>> +		threshold to 1.
>>
>>      nomce (for compatibility with i386): same as mce=off
>>
>> diff --git a/arch/x86/include/asm/mce.h b/arch/x86/include/asm/mce.h
>> index a3ac52b..8ad5078 100644
>> --- a/arch/x86/include/asm/mce.h
>> +++ b/arch/x86/include/asm/mce.h
>> @@ -171,6 +171,7 @@ DECLARE_PER_CPU(struct device *, mce_device);
>>   #ifdef CONFIG_X86_MCE_INTEL
>>   extern int mce_cmci_disabled;
>>   extern int mce_ignore_ce;
>> +extern int mce_bios_cmci_threshold;
>>   void mce_intel_feature_init(struct cpuinfo_x86 *c);
>>   void cmci_clear(void);
>>   void cmci_reenable(void);
>> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
>> index 292d025..401359d 100644
>> --- a/arch/x86/kernel/cpu/mcheck/mce.c
>> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
>> @@ -82,6 +82,7 @@ static int			mce_panic_timeout	__read_mostly;
>>   static int			mce_dont_log_ce		__read_mostly;
>>   int				mce_cmci_disabled	__read_mostly;
>>   int				mce_ignore_ce		__read_mostly;
>> +int				mce_bios_cmci_threshold	__read_mostly;
>>   int				mce_ser			__read_mostly;
>
> AFAICT, this is actually a single-bit flag but we're using a whole
> integer for it and from looking at the other boot options a couple of
> them are used as flags too.
>
> Care to define a
>
> struct boot_flags {
> 	__u64 	mce_bios_cmci_threshold : 1,
> 		__reserved		: 63;
> };
>
> and use
>
> 	boot_flags.mce_bios_cmci_threshold
>
> in the conditionals below instead?

Sure - sounds like a good idea. Further, a #define could eliminate the 
need to change other references, but I'm not sure that's GENERALLacceptable

#define mce_bios_cmci_threshold boot_flags.mce_bios_cmci_threshold

could eliminate the need to change other references, but I'm not sure 
that's acceptable

But, I just had a quick look and it seems to me that these were defined 
as integers since they are exposed via sysfs. For instance:

static struct dev_ext_attribute dev_attr_cmci_disabled = {
         __ATTR(cmci_disabled, 0644, device_show_int, set_cmci_disabled),
         &mce_cmci_disabled
};

Converting mce_cmci_disabled to a bit-field doesn't work since we take 
its address above. We could ignore and not set the second field at all 
(dev_ext_attribute->var) and define our own callbacks, but that'll be 
more work and I'm not sure if we work fine without


>
> I'll try to convert the rest of them to that struct and thus save some
> more space...
>
> Thanks.
>

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