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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 E85DAC433DF for ; Thu, 28 May 2020 20:52:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE39D2074B for ; Thu, 28 May 2020 20:52:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407386AbgE1Uwk (ORCPT ); Thu, 28 May 2020 16:52:40 -0400 Received: from ppsw-31.csi.cam.ac.uk ([131.111.8.131]:50024 "EHLO ppsw-31.csi.cam.ac.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2407319AbgE1Uwi (ORCPT ); Thu, 28 May 2020 16:52:38 -0400 X-Cam-AntiVirus: no malware found X-Cam-ScannerInfo: http://help.uis.cam.ac.uk/email-scanner-virus Received: from 88-109-182-220.dynamic.dsl.as9105.com ([88.109.182.220]:59746 helo=[192.168.1.219]) by ppsw-31.csi.cam.ac.uk (smtp.hermes.cam.ac.uk [131.111.8.157]:465) with esmtpsa (PLAIN:amc96) (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) id 1jePVv-000XAe-LF (Exim 4.92.3) (return-path ); Thu, 28 May 2020 21:52:31 +0100 Subject: Re: [PATCH 1/6] x86/entry: Introduce local_db_{save,restore}() To: Peter Zijlstra , tglx@linutronix.de, luto@amacapital.net Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Lai Jiangshan , sean.j.christopherson@intel.com, daniel.thompson@linaro.org References: <20200528201937.038455891@infradead.org> <20200528202328.418625592@infradead.org> From: Andrew Cooper Message-ID: <17e097f5-f92c-bd7e-fb1d-ee08c4169dbe@citrix.com> Date: Thu, 28 May 2020 21:52:30 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200528202328.418625592@infradead.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/05/2020 21:19, Peter Zijlstra wrote: > --- a/arch/x86/include/asm/debugreg.h > +++ b/arch/x86/include/asm/debugreg.h > @@ -113,6 +113,31 @@ static inline void debug_stack_usage_inc > static inline void debug_stack_usage_dec(void) { } > #endif /* X86_64 */ > > +static __always_inline void local_db_save(unsigned long *dr7) > +{ > + get_debugreg(*dr7, 7); > + if (*dr7) > + set_debugreg(0, 7); %dr7 has an architecturally stuck bit in it. You want *dr7 != 0x400 to avoid writing 0 unconditionally. Also, API wise, wouldn't it be nicer to write "dr7 = local_db_save()" rather than having a void function returning a single long via pointer? ~Andrew