From owner-svn-src-all@freebsd.org Thu Sep 20 13:29:44 2018 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 9191E109CD12; Thu, 20 Sep 2018 13:29:44 +0000 (UTC) (envelope-from mjg@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 48A588D120; Thu, 20 Sep 2018 13:29:44 +0000 (UTC) (envelope-from mjg@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 41FE91E8B3; Thu, 20 Sep 2018 13:29:44 +0000 (UTC) (envelope-from mjg@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id w8KDTiKg008871; Thu, 20 Sep 2018 13:29:44 GMT (envelope-from mjg@FreeBSD.org) Received: (from mjg@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id w8KDTiab008870; Thu, 20 Sep 2018 13:29:44 GMT (envelope-from mjg@FreeBSD.org) Message-Id: <201809201329.w8KDTiab008870@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: mjg set sender to mjg@FreeBSD.org using -f From: Mateusz Guzik Date: Thu, 20 Sep 2018 13:29:44 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r338828 - head/sys/amd64/amd64 X-SVN-Group: head X-SVN-Commit-Author: mjg X-SVN-Commit-Paths: head/sys/amd64/amd64 X-SVN-Commit-Revision: 338828 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.27 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 20 Sep 2018 13:29:44 -0000 Author: mjg Date: Thu Sep 20 13:29:43 2018 New Revision: 338828 URL: https://svnweb.freebsd.org/changeset/base/338828 Log: amd64: move fusufault after all users A lot of function have the following check: cmpq %rax,%rdi /* verify address is valid */ ja fusufault The label is present earlier in kernel .text, which means this is a jump backwards. Absent any information in branch predictor, the cpu predicts it as taken. Since it is almost never taken in practice, this results in a completely avoidable misprediction. Move it past all consumers, so that it is predicted as not taken. Approved by: re (kib) Modified: head/sys/amd64/amd64/support.S Modified: head/sys/amd64/amd64/support.S ============================================================================== --- head/sys/amd64/amd64/support.S Thu Sep 20 11:44:36 2018 (r338827) +++ head/sys/amd64/amd64/support.S Thu Sep 20 13:29:43 2018 (r338828) @@ -755,16 +755,6 @@ ENTRY(fubyte_smap) ret END(fubyte_smap) - ALIGN_TEXT - /* Fault entry clears PSL.AC */ -fusufault: - movq PCPU(CURPCB),%rcx - xorl %eax,%eax - movq %rax,PCB_ONFAULT(%rcx) - decq %rax - POP_FRAME_POINTER - ret - /* * Store a 64-bit word, a 32-bit word, a 16-bit word, or an 8-bit byte to * user memory. @@ -915,6 +905,16 @@ ENTRY(subyte_smap) POP_FRAME_POINTER ret END(subyte_smap) + + ALIGN_TEXT + /* Fault entry clears PSL.AC */ +fusufault: + movq PCPU(CURPCB),%rcx + xorl %eax,%eax + movq %rax,PCB_ONFAULT(%rcx) + decq %rax + POP_FRAME_POINTER + ret /* * copyinstr(from, to, maxlen, int *lencopied)