From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AB27EC43381 for ; Thu, 21 Mar 2019 20:29:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 831AD21925 for ; Thu, 21 Mar 2019 20:29:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729222AbfCUU3F (ORCPT ); Thu, 21 Mar 2019 16:29:05 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:39355 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728932AbfCUU0u (ORCPT ); Thu, 21 Mar 2019 16:26:50 -0400 Received: from localhost ([127.0.0.1] helo=flow.W.breakpoint.cc) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1h74H0-00057y-7C; Thu, 21 Mar 2019 21:26:46 +0100 From: Sebastian Andrzej Siewior To: linux-kernel@vger.kernel.org Cc: x86@kernel.org, Andy Lutomirski , Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , kvm@vger.kernel.org, "Jason A. Donenfeld" , Rik van Riel , Dave Hansen , Sebastian Andrzej Siewior Subject: [PATCH 14/24] x86/pkeys: Don't check if PKRU is zero before writting it Date: Thu, 21 Mar 2019 21:26:22 +0100 Message-Id: <20190321202632.16810-15-bigeasy@linutronix.de> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190321202632.16810-1-bigeasy@linutronix.de> References: <20190321202632.16810-1-bigeasy@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org write_pkru() checks if the current value is the same as the expected value. So instead just checking if the current and new value is zero (and skip the write in such a case) we can benefit from that. Remove the zero check of PKRU, write_pkru() provides a similar check. Signed-off-by: Sebastian Andrzej Siewior --- arch/x86/mm/pkeys.c | 7 ------- 1 file changed, 7 deletions(-) diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c index 05bb9a44eb1c3..50f65fc1b9a3f 100644 --- a/arch/x86/mm/pkeys.c +++ b/arch/x86/mm/pkeys.c @@ -142,13 +142,6 @@ u32 init_pkru_value = PKRU_AD_KEY( 1) | PKRU_AD_KEY( 2) | PKRU_AD_KEY( 3) | void copy_init_pkru_to_fpregs(void) { u32 init_pkru_value_snapshot = READ_ONCE(init_pkru_value); - /* - * Any write to PKRU takes it out of the XSAVE 'init - * state' which increases context switch cost. Avoid - * writing 0 when PKRU was already 0. - */ - if (!init_pkru_value_snapshot && !read_pkru()) - return; /* * Override the PKRU state that came from 'init_fpstate' * with the baseline from the process. -- 2.20.1