From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267610AbUHMWZu (ORCPT ); Fri, 13 Aug 2004 18:25:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S267615AbUHMWZt (ORCPT ); Fri, 13 Aug 2004 18:25:49 -0400 Received: from mailout1.vmware.com ([65.113.40.130]:63498 "EHLO mailout1.vmware.com") by vger.kernel.org with ESMTP id S267610AbUHMWZl (ORCPT ); Fri, 13 Aug 2004 18:25:41 -0400 Message-ID: <411D3C24.4030006@vmware.com> Date: Fri, 13 Aug 2004 15:09:40 -0700 From: Zachary Amsden User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.2) Gecko/20040803 X-Accept-Language: en-us, en MIME-Version: 1.0 To: linux-kernel@vger.kernel.org, davej@codemonkey.org, hpa@zytor.com Subject: [PATCH] i386 - remove unnecessary unbusy TSS code Content-Type: multipart/mixed; boundary="------------010702030605090307070203" X-OriginalArrivalTime: 13 Aug 2004 22:09:40.0127 (UTC) FILETIME=[3A8D0AF0:01C48182] X-AntiVirus: checked by Vexira MailArmor (version: 2.0.1.16; VAE: 6.27.0.4; VDF: 6.27.0.10; host: mailhost1.vmware.com) X-AntiVirus: checked by Vexira MailArmor (version: 2.0.1.16; VAE: 6.27.0.4; VDF: 6.27.0.10; host: mailout1.vmware.com) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org This is a multi-part message in MIME format. --------------010702030605090307070203 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit I was looking at GDT updates in the Linux kernel and noticed some redundant code in initialization of the per-CPU GDT. This code is no longer necessary or commented, so I removed it for simplicity (and it saves 20 bytes of code space). Version: patched against 2.6.7 Testing: compile and boot a Linux 2.6.7 kernel with my patch. --------------010702030605090307070203 Content-Type: text/plain; name="README.gdt-unbusy" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="README.gdt-unbusy" The TSS no longer needs to be unbusied before loading the task register, since the set_tss_desc macros set the system gate type to Available IA-32 TSS. This obscure, uncommented legacy code can now be removed for better readability and saves 20 bytes of code space. Here is a breakdown of __set_tss_desc + load_TR before and after. The doublefault TSS GDT setup has similar savings. - Zachary Amsden (zach@vmware.com) before: c01d4535: ba 80 20 1b c0 mov $0xc01b2080,%edx c01d453a: b8 00 d8 1c c0 mov $0xc01cd800,%eax c01d453f: 66 c7 42 00 eb 00 movw $0xeb,0x0(%edx) c01d4545: 66 89 42 02 mov %ax,0x2(%edx) c01d4549: c1 c8 10 ror $0x10,%eax c01d454c: 88 42 04 mov %al,0x4(%edx) c01d454f: c6 42 05 89 movb $0x89,0x5(%edx) ^^ non-busy c01d4553: c6 42 06 00 movb $0x0,0x6(%edx) c01d4557: 88 62 07 mov %ah,0x7(%edx) c01d455a: c1 c8 10 ror $0x10,%eax c01d455d: 81 25 84 20 1b c0 ff andl $0xfffffdff,0xc01b2084 c01d4564: fd ff ff c01d4567: b8 80 00 00 00 mov $0x80,%eax c01d456c: 0f 00 d8 ltr %ax now: c01d4535: ba 80 20 1b c0 mov $0xc01b2080,%edx c01d453a: b8 00 d8 1c c0 mov $0xc01cd800,%eax c01d453f: 66 c7 42 00 eb 00 movw $0xeb,0x0(%edx) c01d4545: 66 89 42 02 mov %ax,0x2(%edx) c01d4549: c1 c8 10 ror $0x10,%eax c01d454c: 88 42 04 mov %al,0x4(%edx) c01d454f: c6 42 05 89 movb $0x89,0x5(%edx) c01d4553: c6 42 06 00 movb $0x0,0x6(%edx) c01d4557: 88 62 07 mov %ah,0x7(%edx) c01d455a: c1 c8 10 ror $0x10,%eax c01d455d: b8 80 00 00 00 mov $0x80,%eax c01d4562: 0f 00 d8 ltr %ax --------------010702030605090307070203 Content-Type: text/plain; name="gdt-unbusy.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="gdt-unbusy.patch" --- arch/i386/kernel/cpu/common.c.orig 2004-08-13 14:16:28.000000000 -0700 +++ arch/i386/kernel/cpu/common.c 2004-08-13 14:16:46.000000000 -0700 @@ -552,13 +552,11 @@ load_esp0(t, thread); set_tss_desc(cpu,t); - cpu_gdt_table[cpu][GDT_ENTRY_TSS].b &= 0xfffffdff; load_TR_desc(); load_LDT(&init_mm.context); /* Set up doublefault TSS pointer in the GDT */ __set_tss_desc(cpu, GDT_ENTRY_DOUBLEFAULT_TSS, &doublefault_tss); - cpu_gdt_table[cpu][GDT_ENTRY_DOUBLEFAULT_TSS].b &= 0xfffffdff; /* Clear %fs and %gs. */ asm volatile ("xorl %eax, %eax; movl %eax, %fs; movl %eax, %gs"); --------------010702030605090307070203--