linux-kernel - Kernel broken on processors without performance counters

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Message-ID: <alpine.LRH.2.02.1507081000540.5217@file01.intranet.prod.int.rdu2.redhat.com>
Date:	Wed, 8 Jul 2015 11:17:38 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>,
	Peter Zijlstra <peterz@...radead.org>
cc:	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Kees Cook <keescook@...omium.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Vince Weaver <vince@...ter.net>,
	"hillf.zj" <hillf.zj@...baba-inc.com>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	linux-kernel@...r.kernel.org
Subject: Kernel broken on processors without performance counters

Hi

I found out that the patch a66734297f78707ce39d756b656bfae861d53f62 breaks 
the kernel on processors without performance counters, such as AMD K6-3. 
Reverting the patch fixes the problem.

The static key rdpmc_always_available somehow gets set (I couldn't really 
find out what is setting it, the function set_attr_rdpmc is not executed), 
cr4_set_bits(X86_CR4_PCE) is executed and that results in a crash on boot 
when attempting to execute init, because the proecssor doesn't support 
that bit in CR4.

Mikulas
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