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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 7F944C4360C for ; Fri, 4 Oct 2019 11:25:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 202D12070B for ; Fri, 4 Oct 2019 11:25:05 +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="ZnsQjPYP" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 202D12070B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 883CF6B0003; Fri, 4 Oct 2019 07:25:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 80BA96B0005; Fri, 4 Oct 2019 07:25:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6848E6B0007; Fri, 4 Oct 2019 07:25:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0203.hostedemail.com [216.40.44.203]) by kanga.kvack.org (Postfix) with ESMTP id 4016D6B0003 for ; Fri, 4 Oct 2019 07:25:04 -0400 (EDT) Received: from smtpin01.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id CE17545A0 for ; Fri, 4 Oct 2019 11:25:03 +0000 (UTC) X-FDA: 76005870486.01.music39_2c20f161f8136 X-HE-Tag: music39_2c20f161f8136 X-Filterd-Recvd-Size: 6023 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf08.hostedemail.com (Postfix) with ESMTP for ; Fri, 4 Oct 2019 11:25:03 +0000 (UTC) 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=RXKGx8X/1FKuOuVTe5a+zqWHCcREtJtzpf0mmOIuvz8=; b=ZnsQjPYPqZqfl38X4184WJZaF IYI0tUAi3WvtFfwDF0F7a/z/9DOD3bKMVBAWXGmHRNf7hNtFvXJvmis0Vx2M21gA7KXvL/dhCzCb/ u5a5KdVT6IZKTbJ44Y1idOc//bRcOX9/SKd8UzoqsZkGsVLIY1NjnS2kkt+LesFbCQy0e0E+HXzMk EjbwXR2oPQO67RrgJR4a2azNCgtEzeN2UpIRClq45dXeObg7fRoZC+8hTQpdNmwXMmhSVkwSRczJv Sgtn+GLMpXxswWi2KXhjwrRntT6prFNu60S3ZLgFuy3kWbwoYAIc5BDl8xIJwPWMPOI5wQzyTOcWz YAkdtWSzA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.2 #3 (Red Hat Linux)) id 1iGLhD-0000Hy-LH; Fri, 04 Oct 2019 11:24:27 +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 DD6E9305ED5; Fri, 4 Oct 2019 13:23:31 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 60366203E50D2; Fri, 4 Oct 2019 13:24:21 +0200 (CEST) Date: Fri, 4 Oct 2019 13:24:21 +0200 From: Peter Zijlstra To: John Hubbard Cc: Leonardo Bras , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Arnd Bergmann , "Aneesh Kumar K.V" , Christophe Leroy , Nicholas Piggin , Andrew Morton , Mahesh Salgaonkar , Reza Arbab , Santosh Sivaraj , Balbir Singh , Thomas Gleixner , Greg Kroah-Hartman , Mike Rapoport , Allison Randal , Jason Gunthorpe , Dan Williams , Vlastimil Babka , Christoph Lameter , Logan Gunthorpe , Andrey Ryabinin , Alexey Dobriyan , Souptick Joarder , Mathieu Desnoyers , Ralph Campbell , Jesper Dangaard Brouer , Jann Horn , Davidlohr Bueso , Ingo Molnar , Christian Brauner , Michal Hocko , Elena Reshetova , Roman Gushchin , Andrea Arcangeli , Al Viro , "Dmitry V. Levin" , =?iso-8859-1?B?Suly9G1l?= Glisse , Song Liu , Bartlomiej Zolnierkiewicz , Ira Weiny , "Kirill A. Shutemov" , Keith Busch , Paul McKenney Subject: Re: [PATCH v5 01/11] asm-generic/pgtable: Adds generic functions to monitor lockless pgtable walks Message-ID: <20191004112421.GB19463@hirez.programming.kicks-ass.net> References: <20191003013325.2614-1-leonardo@linux.ibm.com> <20191003013325.2614-2-leonardo@linux.ibm.com> <20191003071145.GM4536@hirez.programming.kicks-ass.net> <20191003115141.GJ4581@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Oct 03, 2019 at 01:40:38PM -0700, John Hubbard wrote: > On 10/3/19 4:51 AM, Peter Zijlstra wrote: > > On Thu, Oct 03, 2019 at 09:11:45AM +0200, Peter Zijlstra wrote: > >> On Wed, Oct 02, 2019 at 10:33:15PM -0300, Leonardo Bras wrote: > ... > > > > I'm still really confused about this barrier. It just doesn't make > > sense. > > > > If an interrupt happens before the local_irq_disable()/save(), then it > > will discard any and all speculation that would be in progress to handle > > the exception. > > > > Hi Peter, > > So, would that imply that it's correct to apply approximately the following > patch: > > diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt > index 1adbb8a371c7..cf41eff37e24 100644 > --- a/Documentation/memory-barriers.txt > +++ b/Documentation/memory-barriers.txt > @@ -2099,9 +2099,9 @@ INTERRUPT DISABLING FUNCTIONS > ----------------------------- > > Functions that disable interrupts (ACQUIRE equivalent) and enable interrupts > -(RELEASE equivalent) will act as compiler barriers only. So if memory or I/O > -barriers are required in such a situation, they must be provided from some > -other means. > +(RELEASE equivalent) will act as full memory barriers. This is because, for > +all supported CPU architectures, interrupt arrival causes all speculative > +memory accesses to be discarded. > > ? No, you're misunderstanding. They imply nothing of the sort.