linux-kernel - Re: [PATCH v2 07/16] x86/mce/amd: Simplify DFR handler setup

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Message-ID: <20240429141244.GGZi-q3NdmI17pai4N@fat_crate.local>
Date: Mon, 29 Apr 2024 16:12:44 +0200
From: Borislav Petkov <bp@...en8.de>
To: Yazen Ghannam <yazen.ghannam@....com>
Cc: robert.richter@....com, linux-edac@...r.kernel.org,
	linux-kernel@...r.kernel.org, tony.luck@...el.com, x86@...nel.org,
	Avadhut.Naik@....com, John.Allen@....com
Subject: Re: [PATCH v2 07/16] x86/mce/amd: Simplify DFR handler setup

On Mon, Apr 29, 2024 at 09:56:56AM -0400, Yazen Ghannam wrote:
> Right, I mean we should do things the simpler way unless there's a real issue
> to address.

You need to pay attention to past issues before you go, simplify it and
break it again.

> I'm not opposed to this, but I don't understand what is at risk.
> 
> Is it that the function pointer may not be written atomically? So even if we
> write it again with the same value, a concurrent interrupt on another core may
> see a partially updated (corrupt) pointer?

Yes, it won't happen, they say as it is guaranteed by the
architecture. But I've heard those "promises".

> intel_init_cmci() does not do this check. So is it more at risk, or is the AMD
> code just more cautious?
> 
> Again I'm not against the current code. I just think we should simplify it, if
> possible.

So in looking at the INTR_CFG MSR, I think we should do a function which
does MCA init stuff only on the BSP exactly for things like that.

There you can set the interrupt handler pointer, the INTR_CFG MSR and so
on. And we don't have such function and I've needed a function like that
in the past.

And just for the general goal of not doing ugly code which should run
only once but is run per-CPU just because our infrastructure doesn't
allow it.

Wanna give that a try?

Thx.

-- 
Regards/Gruss,
    Boris.

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