linux-kernel - Re: [PATCH] perf/x86: check ucode before disabling PEBS on SandyBridge

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Date:	Tue, 12 Jun 2012 19:35:06 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Borislav Petkov <bp@...64.org>,
	Stephane Eranian <eranian@...gle.com>,
	Robert Richter <robert.richter@....com>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, mingo@...e.hu, ming.m.lin@...el.com,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Dimitri Sivanich <sivanich@....com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: Re: [PATCH] perf/x86: check ucode before disabling PEBS on
 SandyBridge

On Tue, Jun 12, 2012 at 07:26:36PM +0200, Peter Zijlstra wrote:
> You want, yes, but afaict the stuff in
> arch/x86/kernel/microcode_core.c:reload_store means you can force a
> single cpu to update while leaving the others alone.

Btw, this doesn't work on AMD... for a reason.

> Afaict this is not a sane thing to do, but quite possible.

I'd guess this is still there to support mixed ucode revisions for some
oldish platforms. But if SB doesn't support mixed ucode revisions,
you don't want to use the reload_store interface anyway for reasons
described above. Maybe this interface should be behind a family, model
check or so, so that users don't shoot themselves in the foot but it is
root-only anyway.

-- 
Regards/Gruss,
Boris.

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