From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756409Ab3GDI6m (ORCPT ); Thu, 4 Jul 2013 04:58:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:3311 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751381Ab3GDI6j (ORCPT ); Thu, 4 Jul 2013 04:58:39 -0400 From: Denys Vlasenko To: Gleb Natapov , linux-kernel@vger.kernel.org Cc: Denys Vlasenko , Paolo Bonzini , Avi Kivity Subject: [PATCH] x86/kvm/emulate.c: simplify NOP (opcode 0x90) check Date: Thu, 4 Jul 2013 10:58:29 +0200 Message-Id: <1372928309-16488-1-git-send-email-dvlasenk@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The check sits in switch() statement which itself can check for opcode 0x90 far more efficiently. On assembler level, this change simply eliminates the following bit of code: 4c 8b a3 d8 00 00 00 mov 0xd8(%rbx),%r12 31 f6 xor %esi,%esi 48 89 df mov %rbx,%rdi e8 32 8c ff ff callq 490 48 8d 83 78 01 00 00 lea 0x178(%rbx),%rax 83 8b 70 01 00 00 01 orl $0x1,0x170(%rbx) 83 8b 74 01 00 00 01 orl $0x1,0x174(%rbx) 49 39 c4 cmp %rax,%r12 0f 84 88 fa ff ff je 7304 Signed-off-by: Denys Vlasenko CC: Paolo Bonzini CC: Avi Kivity --- arch/x86/kvm/emulate.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 2bc1e81..7e6e74a 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4544,9 +4544,9 @@ special_insn: case 0x8d: /* lea r16/r32, m */ ctxt->dst.val = ctxt->src.addr.mem.ea; break; - case 0x90 ... 0x97: /* nop / xchg reg, rax */ - if (ctxt->dst.addr.reg == reg_rmw(ctxt, VCPU_REGS_RAX)) - break; + case 0x90: /* nop */ + break; + case 0x91 ... 0x97: /* xchg reg, rax */ rc = em_xchg(ctxt); break; case 0x98: /* cbw/cwde/cdqe */ -- 1.8.1.4