linux-kernel - Re: [PATCH 3/6] x86/mce: Add support for new MCA

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Message-ID: <20160708092659.GB13849@gmail.com>
Date:	Fri, 8 Jul 2016 11:26:59 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Yazen Ghannam <Yazen.Ghannam@....com>
Subject: Re: [PATCH 3/6] x86/mce: Add support for new MCA_SYND register


* Borislav Petkov <bp@...en8.de> wrote:

> From: Yazen Ghannam <Yazen.Ghannam@....com>
> 
> Syndrome information is no longer contained in MCA_STATUS for SMCA
> systems but in a new register.
> 
> Add a synd field to struct mce to hold MCA_SYND register value. Add it
> to the end of struct mce to maintain compatibility with old versions of
> mcelog. Also, add it to the respective tracepoint.

>  /* AMD-specific bits */
> +#define MCI_STATUS_TCC		(1ULL<<55)  /* Task context corrupt */
> +#define MCI_STATUS_SYNDV	(1ULL<<53)  /* synd reg. valid */

> --- a/arch/x86/include/uapi/asm/mce.h
> +++ b/arch/x86/include/uapi/asm/mce.h
> @@ -26,6 +26,7 @@ struct mce {
>  	__u32 socketid;	/* CPU socket ID */
>  	__u32 apicid;	/* CPU initial apic ID */
>  	__u64 mcgcap;	/* MCGCAP MSR: machine check capabilities of CPU */
> +	__u64 synd;	/* MCA_SYND MSR: only valid on SMCA systems */
>  };

So why does neither the changelog nor the code comment actually _explain_ this and 
give aa bit of a background about what 'syndrome information' is and why we want 
to have kernel support for it?

This is why I hate kernel tooling that is not part of the kernel tree - the mcelog 
patch (hopefully ...) would tell us more about all this - but it's separate and 
this patch does not tell us anything ...

Thanks,

	Ingo