Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935058AbbGHQyt (ORCPT ); Wed, 8 Jul 2015 12:54:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44106 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758929AbbGHQys (ORCPT ); Wed, 8 Jul 2015 12:54:48 -0400 Date: Wed, 8 Jul 2015 12:54:44 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: Peter Zijlstra cc: Andy Lutomirski , Paul Mackerras , Arnaldo Carvalho de Melo , Kees Cook , Andrea Arcangeli , Vince Weaver , "hillf.zj" , Valdis Kletnieks , linux-kernel@vger.kernel.org Subject: Re: Kernel broken on processors without performance counters In-Reply-To: <20150708160750.GQ19282@twins.programming.kicks-ass.net> Message-ID: References: <20150708160750.GQ19282@twins.programming.kicks-ass.net> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1771 Lines: 50 On Wed, 8 Jul 2015, Peter Zijlstra wrote: > On Wed, Jul 08, 2015 at 11:17:38AM -0400, Mikulas Patocka wrote: > > 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. > > Urgh, the static key trainwreck bites again. > > One is not supposed to mix static_key_true() and STATIC_KEY_INIT_FALSE. > > Does this make it go again? Yes, this patch fixes the problem. Mikulas > --- > arch/x86/include/asm/mmu_context.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h > index 5e8daee7c5c9..804a3a6030ca 100644 > --- a/arch/x86/include/asm/mmu_context.h > +++ b/arch/x86/include/asm/mmu_context.h > @@ -23,7 +23,7 @@ extern struct static_key rdpmc_always_available; > > static inline void load_mm_cr4(struct mm_struct *mm) > { > - if (static_key_true(&rdpmc_always_available) || > + if (static_key_false(&rdpmc_always_available) || > atomic_read(&mm->context.perf_rdpmc_allowed)) > cr4_set_bits(X86_CR4_PCE); > else > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/