From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 2EFF37D043 for ; Mon, 11 Jun 2018 15:06:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754013AbeFKPGT (ORCPT ); Mon, 11 Jun 2018 11:06:19 -0400 Received: from mga17.intel.com ([192.55.52.151]:34531 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752452AbeFKPGS (ORCPT ); Mon, 11 Jun 2018 11:06:18 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Jun 2018 08:06:03 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.49,502,1520924400"; d="scan'208";a="48445016" Received: from unknown (HELO [143.183.136.147]) ([143.183.136.147]) by orsmga008.jf.intel.com with ESMTP; 11 Jun 2018 08:06:02 -0700 Message-ID: <1528729376.4526.0.camel@2b52.sc.intel.com> Subject: Re: [PATCH 02/10] x86/cet: Introduce WRUSS instruction From: Yu-cheng Yu To: Peter Zijlstra Cc: Andy Lutomirski , LKML , linux-doc@vger.kernel.org, Linux-MM , linux-arch , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , "H. J. Lu" , "Shanbhogue, Vedvyas" , "Ravi V. Shankar" , Dave Hansen , Jonathan Corbet , Oleg Nesterov , Arnd Bergmann , mike.kravetz@oracle.com Date: Mon, 11 Jun 2018 08:02:56 -0700 In-Reply-To: <20180611081704.GI12180@hirez.programming.kicks-ass.net> References: <20180607143807.3611-1-yu-cheng.yu@intel.com> <20180607143807.3611-3-yu-cheng.yu@intel.com> <20180611081704.GI12180@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Mon, 2018-06-11 at 10:17 +0200, Peter Zijlstra wrote: > On Thu, Jun 07, 2018 at 09:40:02AM -0700, Andy Lutomirski wrote: > > On Thu, Jun 7, 2018 at 7:41 AM Yu-cheng Yu wrote: > > > Peterz, isn't there some fancy better way we're supposed to handle the > > error return these days? > > > > + asm volatile("1:.byte 0x66, 0x0f, 0x38, 0xf5, 0x37\n" > > > + "xor %[err],%[err]\n" > > > + "2:\n" > > > + ".section .fixup,\"ax\"\n" > > > + "3: mov $-1,%[err]; jmp 2b\n" > > > + ".previous\n" > > > + _ASM_EXTABLE(1b, 3b) > > > + : [err] "=a" (err) > > > + : [val] "S" (val), [addr] "D" (addr) > > > + : "memory"); > > So the alternative is something like: > > __visible bool ex_handler_wuss(const struct exception_table_entry *fixup, > struct pt_regs *regs, int trapnr) > { > regs->ip = ex_fixup_addr(fixup); > regs->ax = -1L; > > return true; > } > > > int err = 0; > > asm volatile("1: INSN_WUSS\n" > "2:\n" > _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_wuss) > : "=a" (err) > : "S" (val), "D" (addr)); > > But I'm not at all sure that's actually better. Thanks! I will fix it. Yu-cheng -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html