linux-kernel - Re: [PATCH 3/5] x86/mce: Add new "handled" field to "struct mce"

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Date:   Thu, 13 Feb 2020 17:56:17 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Tony Luck <tony.luck@...el.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] x86/mce: Add new "handled" field to "struct mce"

On Wed, Feb 12, 2020 at 12:46:50PM -0800, Tony Luck wrote:
> There can be many different subsystems register on the mce handler
> chain. Add a new bitmask field and define values so that handlers
> can indicate whether they took any action to log or otherwise
> handle an error.
> 
> The default handler at the end of the chain can use this information
> to decide whether to print to the console log.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  arch/x86/include/uapi/asm/mce.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/x86/include/uapi/asm/mce.h b/arch/x86/include/uapi/asm/mce.h
> index 955c2a2e1cf9..99ca07f7b078 100644
> --- a/arch/x86/include/uapi/asm/mce.h
> +++ b/arch/x86/include/uapi/asm/mce.h
> @@ -35,8 +35,17 @@ struct mce {
>  	__u64 ipid;		/* MCA_IPID MSR: only valid on SMCA systems */
>  	__u64 ppin;		/* Protected Processor Inventory Number */
>  	__u32 microcode;	/* Microcode revision */
> +	__u32 handled;		/* Bitmap of logging/handling actions */
>  };
>  
> +/* handled flag bits */
> +#define	MCE_HANDLED_CEC		BIT(0)
> +#define	MCE_HANDLED_UC		BIT(1)
> +#define	MCE_HANDLED_EXTLOG	BIT(2)
> +#define	MCE_HANDLED_NFIT	BIT(3)
> +#define	MCE_HANDLED_EDAC	BIT(4)
> +#define	MCE_HANDLED_MCELOG	BIT(5)
> +
>  #define MCE_GET_RECORD_LEN   _IOR('M', 1, int)
>  #define MCE_GET_LOG_LEN      _IOR('M', 2, int)
>  #define MCE_GETCLEAR_FLAGS   _IOR('M', 3, int)
> -- 

Not sure if this should be exposed to user. I don't think it has any
business poking its nose into how the MCE was handled. Or maybe it does
but I cannot think of a good example ATM.

If not, this could be

	...
	void *private;
};

which userspace can't make any assumptions about. And we can put
whatever we need in there...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette