From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935342AbcCJLCj (ORCPT ); Thu, 10 Mar 2016 06:02:39 -0500 Received: from torg.zytor.com ([198.137.202.12]:37974 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932236AbcCJLCa (ORCPT ); Thu, 10 Mar 2016 06:02:30 -0500 Date: Thu, 10 Mar 2016 03:01:06 -0800 From: tip-bot for Andy Lutomirski Message-ID: Cc: luto@amacapital.net, brgerst@gmail.com, oleg@redhat.com, peterz@infradead.org, tglx@linutronix.de, bp@alien8.de, luto@kernel.org, andrew.cooper3@citrix.com, torvalds@linux-foundation.org, hpa@zytor.com, mingo@kernel.org, dvlasenk@redhat.com, linux-kernel@vger.kernel.org Reply-To: mingo@kernel.org, hpa@zytor.com, torvalds@linux-foundation.org, dvlasenk@redhat.com, linux-kernel@vger.kernel.org, andrew.cooper3@citrix.com, luto@kernel.org, bp@alien8.de, brgerst@gmail.com, luto@amacapital.net, tglx@linutronix.de, oleg@redhat.com, peterz@infradead.org In-Reply-To: <90d6db2189f9add83bc7bddd75a0c19ebbd676b2.1457578375.git.luto@kernel.org> References: <90d6db2189f9add83bc7bddd75a0c19ebbd676b2.1457578375.git.luto@kernel.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/asm] x86/entry/compat: In SYSENTER, sink AC clearing below the existing FLAGS test Git-Commit-ID: e786041153df6343169373177248abfab5c5ac1b X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: e786041153df6343169373177248abfab5c5ac1b Gitweb: http://git.kernel.org/tip/e786041153df6343169373177248abfab5c5ac1b Author: Andy Lutomirski AuthorDate: Wed, 9 Mar 2016 19:00:25 -0800 Committer: Ingo Molnar CommitDate: Thu, 10 Mar 2016 09:48:12 +0100 x86/entry/compat: In SYSENTER, sink AC clearing below the existing FLAGS test CLAC is slow, and the SYSENTER code already has an unlikely path that runs if unusual flags are set. Drop the CLAC and instead rely on the unlikely path to clear AC. This seems to save ~24 cycles on my Skylake laptop. (Hey, Intel, make this faster please!) Signed-off-by: Andy Lutomirski Cc: Andrew Cooper Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/90d6db2189f9add83bc7bddd75a0c19ebbd676b2.1457578375.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/entry/entry_64_compat.S | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index 3c990ee..da5c194 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -66,8 +66,6 @@ ENTRY(entry_SYSENTER_compat) */ pushfq /* pt_regs->flags (except IF = 0) */ orl $X86_EFLAGS_IF, (%rsp) /* Fix saved flags */ - ASM_CLAC /* Clear AC after saving FLAGS */ - pushq $__USER32_CS /* pt_regs->cs */ xorq %r8,%r8 pushq %r8 /* pt_regs->ip = 0 (placeholder) */ @@ -90,9 +88,9 @@ ENTRY(entry_SYSENTER_compat) cld /* - * Sysenter doesn't filter flags, so we need to clear NT + * SYSENTER doesn't filter flags, so we need to clear NT and AC * ourselves. To save a few cycles, we can check whether - * NT was set instead of doing an unconditional popfq. + * either was set instead of doing an unconditional popfq. * This needs to happen before enabling interrupts so that * we don't get preempted with NT set. * @@ -102,7 +100,7 @@ ENTRY(entry_SYSENTER_compat) * we're keeping that code behind a branch which will predict as * not-taken and therefore its instructions won't be fetched. */ - testl $X86_EFLAGS_NT, EFLAGS(%rsp) + testl $X86_EFLAGS_NT|X86_EFLAGS_AC, EFLAGS(%rsp) jnz .Lsysenter_fix_flags .Lsysenter_flags_fixed: