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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 70601C32771 for ; Mon, 27 Jan 2020 08:36:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 432A2214DB for ; Mon, 27 Jan 2020 08:36:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="atdE9krN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729037AbgA0Igp (ORCPT ); Mon, 27 Jan 2020 03:36:45 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:42752 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725955AbgA0Igo (ORCPT ); Mon, 27 Jan 2020 03:36:44 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=INV8lW4jOqrKHZ5smg8wZ5jkIja+5SUyErQCdgM0jI4=; b=atdE9krN/VqGTwvG06EQuVuXW IAHsjU8r+SDvZCmRtrw6Ys+bnMS+z3DXz8P4phw1VJrzfA9u4l9oGQBPBEmNPoQJUeBity8u6kUJ9 n5e+ZQjPq1yoAuNwuo2T8Tkju/4l4NH1OEuWVIfYu+TFq0QllZYHySDPKUpWMOZzD90OdddHgcci6 7MlXMoIr26/4qDl3CkzxwUkmSeDwMthtymZmm64XUCN478UG48DaoeMzlFG34KS8ga7ReZI93NPCy 23oWsYd4Xl3ptnyBSvjhqeWF9xIuE4RjC5GafiSYTvga9LpzduMM8mz4Cx8T5d5pycQ3LcKG8C1FP zsI1Lcj9Q==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1ivzso-0003gK-3g; Mon, 27 Jan 2020 08:36:34 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 625D2302C0F; Mon, 27 Jan 2020 09:34:50 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 327532019658B; Mon, 27 Jan 2020 09:36:32 +0100 (CET) Date: Mon, 27 Jan 2020 09:36:32 +0100 From: Peter Zijlstra To: "Luck, Tony" Cc: Arvind Sankar , Thomas Gleixner , "Christopherson, Sean J" , Ingo Molnar , "Yu, Fenghua" , Ingo Molnar , Borislav Petkov , H Peter Anvin , "Raj, Ashok" , "Shankar, Ravi V" , linux-kernel , x86 Subject: Re: [PATCH v15] x86/split_lock: Enable split lock detection by kernel Message-ID: <20200127083632.GI14946@hirez.programming.kicks-ass.net> References: <3908561D78D1C84285E8C5FCA982C28F7F54887A@ORSMSX114.amr.corp.intel.com> <20200123004507.GA2403906@rani.riverdale.lan> <20200123035359.GA23659@agluck-desk2.amr.corp.intel.com> <20200123044514.GA2453000@rani.riverdale.lan> <20200123231652.GA4457@agluck-desk2.amr.corp.intel.com> <87h80kmta4.fsf@nanos.tec.linutronix.de> <20200125024727.GA32483@agluck-desk2.amr.corp.intel.com> <20200125212524.GA538225@rani.riverdale.lan> <20200125215003.GB17914@agluck-desk2.amr.corp.intel.com> <20200127080419.GG14914@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200127080419.GG14914@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 27, 2020 at 09:04:19AM +0100, Peter Zijlstra wrote: > On Sat, Jan 25, 2020 at 01:50:03PM -0800, Luck, Tony wrote: > > On Sat, Jan 25, 2020 at 04:25:25PM -0500, Arvind Sankar wrote: > > > On Fri, Jan 24, 2020 at 06:47:27PM -0800, Luck, Tony wrote: > > > > I did find something with a new test. Applications that hit a > > > > split lock warn as expected. But if they sleep before they hit > > > > a new split lock, we get another warning. This is may be because > > > > I messed up when fixing a PeterZ typo in the untested patch. > > > > But I think there may have been bigger problems. > > > > > > > > Context switch in V14 code did: > > > > > > > > if (tifp & _TIF_SLD) > > > > switch_to_sld(prev_p); > > > > > > > > void switch_to_sld(struct task_struct *prev) > > > > { > > > > __sld_msr_set(true); > > > > clear_tsk_thread_flag(prev, TIF_SLD); > > > > } > > > > > > > > Which re-enables split lock checking for the next process to run. But > > > > mysteriously clears the TIF_SLD bit on the previous task. > > > > > > Did Peter mean to disable it only for the current timeslice and > > > re-enable it for the next time its scheduled? > > > > He's seen and commented on this thread since I made this comment. So > > Yeah, I sorta don't care either way :-) Part of the reason I did that was to get the MSR back to enabled ASAP, to limit the blind spot on the sibling. By leaving the TIF_SLD cleared for a task, and using the XOR logic used for other TIF flags, the blind spots will be much larger.