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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 9BB38C63697 for ; Thu, 26 Nov 2020 13:00:11 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B667321D46 for ; Thu, 26 Nov 2020 13:00:10 +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="kwtYBwhP" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B667321D46 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4ChdCB70RrzDqll for ; Fri, 27 Nov 2020 00:00:06 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=infradead.org (client-ip=2001:8b0:10b:1236::1; helo=casper.infradead.org; envelope-from=willy@infradead.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; secure) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=casper.20170209 header.b=kwtYBwhP; dkim-atps=neutral Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4Chd6v3DYYzDqNr for ; Thu, 26 Nov 2020 23:56:23 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=Wzqquq5/8D9FV29EVrzwmTN0u25CnsZPxZTtTznyxuY=; b=kwtYBwhPT/xZPaiK1qJKZ2HGr7 4quVpggBZGhRHOmciM0yyjUsYzXiVZmu3u3Pk0PSig7f3bnc2DnWNmqGhsEXLpcsUy8MqOLtxFiPq yemCSvOVi6L6aCTSF2KLJeKgK0w82yTmoe0CxCovoaDO5mvJy7nZ4nCW8E68MWCxGd2ei90UVJblp wjU+bSg380UGlOMpwS3X7MTXxRAqzF6205FfNpCb7yw6bDwdEkNv5ouvbb9HlNrYY5ea2yPOYigEc K+PjYbYftBbGrPwt+LbQsB5Y9gsJ1NFNEQ3pDT5Lwhzv5zJAgu57y3r7Y1Puc6/9zMPZ9dv+rxV/k q2rhtnRQ==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kiGog-0003FD-PN; Thu, 26 Nov 2020 12:56:07 +0000 Date: Thu, 26 Nov 2020 12:56:06 +0000 From: Matthew Wilcox To: Peter Zijlstra Subject: Re: [PATCH v2 3/6] perf/core: Fix arch_perf_get_page_size() Message-ID: <20201126125606.GR4327@casper.infradead.org> References: <20201126120114.071913521@infradead.org> <20201126121121.164675154@infradead.org> <20201126123458.GO4327@casper.infradead.org> <20201126124207.GM3040@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201126124207.GM3040@hirez.programming.kicks-ass.net> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, aneesh.kumar@linux.ibm.com, linux-arch@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, alexander.shishkin@linux.intel.com, linuxppc-dev@lists.ozlabs.org, npiggin@gmail.com, linux-kernel@vger.kernel.org, acme@kernel.org, davem@davemloft.net, dave.hansen@intel.com, ak@linux.intel.com, eranian@google.com, sparclinux@vger.kernel.org, jolsa@redhat.com, mingo@kernel.org, kirill.shutemov@linux.intel.com, kan.liang@linux.intel.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Nov 26, 2020 at 01:42:07PM +0100, Peter Zijlstra wrote: > + pgdp = pgd_offset(mm, addr); > + pgd = READ_ONCE(*pgdp); I forget how x86-32-PAE maps to Linux's PGD/P4D/PUD/PMD scheme, but according to volume 3, section 4.4.2, PAE paging uses a 64-bit PDE, so whether a PDE is a PGD or a PMD, we're only reading it with READ_ONCE rather than the lockless-retry method used by ptep_get_lockless(). So it's potentially racy? Do we need a pmdp_get_lockless() or pgdp_get_lockless()? [...] > + pmdp = pmd_offset_lockless(pudp, pud, addr); > + pmd = READ_ONCE(*pmdp); > + if (!pmd_present(pmd)) > return 0; > > + if (pmd_leaf(pmd)) > + return pmd_leaf_size(pmd); >