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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 1BF30C433DF for ; Wed, 20 May 2020 09:13:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EA302207F9 for ; Wed, 20 May 2020 09:13:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726806AbgETJNU convert rfc822-to-8bit (ORCPT ); Wed, 20 May 2020 05:13:20 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:55795 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726224AbgETJNT (ORCPT ); Wed, 20 May 2020 05:13:19 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-6-UGwfFmtFPw6X4FXYTYQnQg-1; Wed, 20 May 2020 10:13:15 +0100 X-MC-Unique: UGwfFmtFPw6X4FXYTYQnQg-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Wed, 20 May 2020 10:13:15 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Wed, 20 May 2020 10:13:15 +0100 From: David Laight To: 'Thomas Gleixner' , 'Sasha Levin' CC: "linux-kernel@vger.kernel.org" , "bp@alien8.de" , "luto@kernel.org" , "hpa@zytor.com" , "dave.hansen@intel.com" , "tony.luck@intel.com" , "ak@linux.intel.com" , "ravi.v.shankar@intel.com" , "chang.seok.bae@intel.com" , Andrew Cooper , "x86@kernel.org" Subject: RE: [PATCH v12 10/18] x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions Thread-Topic: [PATCH v12 10/18] x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions Thread-Index: AQHWLVJcG1AiHrfpmEaP5P6pVvKjjqivU+WggAAZtICAAUUdcA== Date: Wed, 20 May 2020 09:13:14 +0000 Message-ID: References: <20200511045311.4785-11-sashal@kernel.org> <87v9ktw1ev.fsf@nanos.tec.linutronix.de> <20200518202435.GD33628@sasha-vm> <238a6e2609eb4e0497b13fbe5f531917@AcuMS.aculab.com> <87r1vg6kwq.fsf@nanos.tec.linutronix.de> In-Reply-To: <87r1vg6kwq.fsf@nanos.tec.linutronix.de> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Thomas Gleixner > Sent: 19 May 2020 15:48 > > David Laight writes: > > From: Sasha Levin > >> >> + native_swapgs(); > >> >> + gsbase = rdgsbase(); > >> >> + native_swapgs(); > > > > Does local_irq_save() even do anything useful here. > > You need to actually execute CLI, not just set a > > flag that indicates interrupts shouldn't happen. > > (Which is what I think local_irq_save() might do.) > > local_irq_save() > raw_local_irq_save() > arch_local_irq_save() > arch_local_irq_disable() > native_irq_disable() > asm("CLI") Ah, I was expecting software 'tricks' to avoid the expensive CLI. But that call chain probably costs more - unless it is all inlined. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)