From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 14 Mar 2002 12:25:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 14 Mar 2002 12:24:59 -0500 Received: from harpo.it.uu.se ([130.238.12.34]:51333 "EHLO harpo.it.uu.se") by vger.kernel.org with ESMTP id ; Thu, 14 Mar 2002 12:24:54 -0500 Date: Thu, 14 Mar 2002 18:24:44 +0100 (MET) From: Mikael Pettersson Message-Id: <200203141724.SAA05707@harpo.it.uu.se> To: alan@lxorguk.ukuu.org.uk, marcelo@conectiva.com.br, torvalds@transmeta.com Subject: [PATCH] boot_cpu_data corruption on SMP x86 Cc: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org The patch below eliminates a case of boot_cpu_data corruption on SMP x86 machines. This was first observed on SMP Athlons, but it also affects SMP Intel boxes in a less serious way. When the secondary processors boot and execute head.S:checkCPUtype, the code performs a 32-bit write of a small constant to the byte-sized variable boot_cpu_data.x86 (X86 in head.S). Since the write is 32-bit, it also writes zeros to the following 3 bytes, which clobbers the x86_vendor, x86_model, and x86_mask fields previously set up by check_bugs()'s call to identify_cpu(). Thus, after smp_init(), boot_cpu_data will _always_ identify the CPU as an Intel (X86_VENDOR_INTEL == 0 in processor.h) with model 0 and stepping 0. The effect in standard kernels is not catastrophic, since: (a) most SMP x86 boxes are Intel (b) most uses of x86_vendor occur before smp_init() or reference the SMP cpu_data[] array (c) most post-boot references to boot_cpu_data occur in the cpu_has_XXX macros which only read the x86_capability[] array However, third-party extensions (like my x86 performance-monitoring conters driver) can get seriously confused by this mis-identification. The patch is for 2.4.19-pre3, but it also applies to 2.5.6 and 2.2.21rc1. Please apply. /Mikael --- linux-2.4.19-pre3/arch/i386/kernel/head.S.~1~ Tue Feb 26 13:26:56 2002 +++ linux-2.4.19-pre3/arch/i386/kernel/head.S Thu Mar 14 16:20:57 2002 @@ -178,7 +178,7 @@ * we don't need to preserve eflags. */ - movl $3,X86 # at least 386 + movb $3,X86 # at least 386 pushfl # push EFLAGS popl %eax # get EFLAGS movl %eax,%ecx # save original EFLAGS @@ -191,7 +191,7 @@ andl $0x40000,%eax # check if AC bit changed je is386 - movl $4,X86 # at least 486 + movb $4,X86 # at least 486 movl %ecx,%eax xorl $0x200000,%eax # check ID flag pushl %eax