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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 173D5C4332F for ; Fri, 14 Oct 2022 12:28:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229884AbiJNM2g convert rfc822-to-8bit (ORCPT ); Fri, 14 Oct 2022 08:28:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59132 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229607AbiJNM2d (ORCPT ); Fri, 14 Oct 2022 08:28:33 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E9C0E164BD6 for ; Fri, 14 Oct 2022 05:28:30 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-91-9xlD7b7vMy-uSIX3ILrAOQ-1; Fri, 14 Oct 2022 13:28:28 +0100 X-MC-Unique: 9xlD7b7vMy-uSIX3ILrAOQ-1 Received: from AcuMS.Aculab.com (10.202.163.6) by AcuMS.aculab.com (10.202.163.6) with Microsoft SMTP Server (TLS) id 15.0.1497.38; Fri, 14 Oct 2022 13:28:26 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.040; Fri, 14 Oct 2022 13:28:26 +0100 From: David Laight To: 'Xin Li' , "linux-kernel@vger.kernel.org" , "x86@kernel.org" CC: "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "hpa@zytor.com" , "peterz@infradead.org" , "brgerst@gmail.com" , "chang.seok.bae@intel.com" Subject: RE: [PATCH v3 3/6] x86/gsseg: make asm_load_gs_index() take an u16 Thread-Topic: [PATCH v3 3/6] x86/gsseg: make asm_load_gs_index() take an u16 Thread-Index: AQHY30Gyx3nzbyqdTEiu3El5Q4Xlsa4N0NzA Date: Fri, 14 Oct 2022 12:28:25 +0000 Message-ID: <86f60a8edf0e458c86cd84970364cfa2@AcuMS.aculab.com> References: <20221013200134.1487-1-xin3.li@intel.com> <20221013200134.1487-4-xin3.li@intel.com> In-Reply-To: <20221013200134.1487-4-xin3.li@intel.com> Accept-Language: en-GB, 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-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Xin Li > Sent: 13 October 2022 21:02 > > From: "H. Peter Anvin (Intel)" > > Let gcc know that only the low 16 bits of load_gs_index() argument > actually matter. It might allow it to create slightly better > code. However, do not propagate this into the prototypes of functions > that end up being paravirtualized, to avoid unnecessary changes. Using u16 will almost always make the code worse. At some point the value has to be masked and/or extended to ensure an out of range value doesn't appear in a register. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)