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

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Date:	Tue, 12 Jun 2012 19:18:13 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Borislav Petkov <bp@...64.org>
Cc:	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, 2012-06-12 at 19:17 +0200, Borislav Petkov wrote:
> On Tue, Jun 12, 2012 at 07:13:23PM +0200, Peter Zijlstra wrote:
> > > That's what I had in my original version.
> > 
> > Right, but you really need to check all cpus, not just the one you
> > happen to run on or the boot cpu.
> 
> Ok, the answer to that question is whether sandybridge can support mixed
> ucode revisions or not. If not, you only need to check the current cpu
> you're on.

But the ucode loader can be (ab)used to only update one of the many
CPUs.
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