From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752180AbbC0Sr6 (ORCPT ); Fri, 27 Mar 2015 14:47:58 -0400 Received: from mail.kernel.org ([198.145.29.136]:49790 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750931AbbC0Sr5 (ORCPT ); Fri, 27 Mar 2015 14:47:57 -0400 From: Andy Lutomirski To: Ingo Molnar , X86 ML Cc: lkml@vger.kernel.org, Denys Vlasenko , Linus Torvalds , Steven Rostedt , Borislav Petkov , "H. Peter Anvin" , Andy Lutomirski , Oleg Nesterov , Frederic Weisbecker , Alexei Starovoitov , Will Drewry , Kees Cook , linux-kernel@vger.kernel.org, Andy Lutomirski Subject: [GIT PULL 2/4] x86: vdso32/syscall.S: do not load __USER32_DS to %ss Date: Fri, 27 Mar 2015 11:47:41 -0700 Message-Id: <63da6d778f69fd0f1345d9287f6764d58be519fa.1427482063.git.luto@kernel.org> X-Mailer: git-send-email 2.3.0 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Denys Vlasenko This vDSO code only gets used by 64-bit kernel, not 32-bit. In 64-bit kernels, data segment is the same for 32-bit and 64-bit userspace, and SYSRET insn does load %ss with its selector. No need to repeat it by hand. Segment loads are somewhat expensive: tens of cycles. Signed-off-by: Denys Vlasenko CC: Linus Torvalds CC: Steven Rostedt CC: Ingo Molnar CC: Borislav Petkov CC: "H. Peter Anvin" CC: Andy Lutomirski CC: Oleg Nesterov CC: Frederic Weisbecker CC: Alexei Starovoitov CC: Will Drewry CC: Kees Cook CC: x86@kernel.org CC: linux-kernel@vger.kernel.org Message-Id: <1427129240-15543-1-git-send-email-dvlasenk@redhat.com> [removed unnecessary comment] Signed-off-by: Andy Lutomirski --- arch/x86/vdso/vdso32/syscall.S | 2 -- 1 file changed, 2 deletions(-) diff --git a/arch/x86/vdso/vdso32/syscall.S b/arch/x86/vdso/vdso32/syscall.S index 5415b5613d55..6b286bb5251c 100644 --- a/arch/x86/vdso/vdso32/syscall.S +++ b/arch/x86/vdso/vdso32/syscall.S @@ -19,8 +19,6 @@ __kernel_vsyscall: .Lpush_ebp: movl %ecx, %ebp syscall - movl $__USER32_DS, %ecx - movl %ecx, %ss movl %ebp, %ecx popl %ebp .Lpop_ebp: -- 2.3.0