Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752321Ab2K2JNY (ORCPT ); Thu, 29 Nov 2012 04:13:24 -0500 Received: from mail.skyhub.de ([78.46.96.112]:50337 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751155Ab2K2JNV (ORCPT ); Thu, 29 Nov 2012 04:13:21 -0500 Date: Thu, 29 Nov 2012 10:13:17 +0100 From: Borislav Petkov To: "H. Peter Anvin" Cc: "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , Linus Torvalds , Linux Kernel Mailing List , Mario Gzuk Subject: Re: [PATCH 8/8] x86, cleanups: Simplify sync_core() in the case of no CPUID Message-ID: <20121129091317.GA21084@liondog.tnic> Mail-Followup-To: Borislav Petkov , "H. Peter Anvin" , "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , Linus Torvalds , Linux Kernel Mailing List , Mario Gzuk References: <1354132230-21854-1-git-send-email-hpa@linux.intel.com> <1354132230-21854-9-git-send-email-hpa@linux.intel.com> <20121128204158.GC14635@liondog.tnic> <50B6A8F3.5000407@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <50B6A8F3.5000407@zytor.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1791 Lines: 77 On Wed, Nov 28, 2012 at 04:14:43PM -0800, H. Peter Anvin wrote: > Wrong barrier semantics. Let me try to understand what you mean by that :) Now, your version's asm output looks like this: ---- .loc 2 95 0 movl $139, %esi #, tmp140 xorl %eax, %eax # tmp141 movl %esi, %ecx # tmp140, movl %eax, %edx # tmp141, #APP # 95 "/home/boris/kernel/linux-2.6/arch/x86/include/asm/msr.h" 1 wrmsr # 0 "" 2 #NO_APP .loc 3 694 0 movb $1, %al #, #APP # 694 "/home/boris/kernel/linux-2.6/arch/x86/include/asm/processor.h" 1 cpuid # 0 "" 2 .LVL15: #NO_APP ---- This is the sync_core() call from early_init_intel(). Now look like 139 remains in %ecx after the WRMSR and CPUID actually gets called with RAX=1 and RCX=139 (btw, 139 is MSR_IA32_UCODE_REV). Even if this works I'd say, we don't want to have any stray values in RCX when doing CPUID, no? Now here's the version with the change I proposed: ---- .loc 2 95 0 xorl %esi, %esi # tmp144 movl $139, %edi #, tmp143 movl %edi, %ecx # tmp143, movl %esi, %eax # tmp144, movl %esi, %edx # tmp144, #APP # 95 "/home/boris/kernel/linux-2.6/arch/x86/include/asm/msr.h" 1 wrmsr # 0 "" 2 .LVL15: #NO_APP .loc 3 199 0 movb $1, %al #, movl %esi, %ecx # tmp144, ecx #APP # 199 "/home/boris/kernel/linux-2.6/arch/x86/include/asm/processor.h" 1 cpuid # 0 "" 2 .LVL16: #NO_APP ---- RCX gets correctly cleaned to 0 and *then* we call CPUID. And the asm output is the same except that RCX gets correctly cleaned up before calling CPUID. So what am I missing? Thanks. -- Regards/Gruss, Boris. -- 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/