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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6FA22C05027 for ; Thu, 26 Jan 2023 21:04:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CC7178E0001; Thu, 26 Jan 2023 16:04:13 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id C76DA6B0075; Thu, 26 Jan 2023 16:04:13 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B3E5F8E0001; Thu, 26 Jan 2023 16:04:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id A53A46B0074 for ; Thu, 26 Jan 2023 16:04:13 -0500 (EST) Received: from smtpin11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 807F140F04 for ; Thu, 26 Jan 2023 21:04:13 +0000 (UTC) X-FDA: 80398177986.11.A7008FC Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) by imf08.hostedemail.com (Postfix) with ESMTP id A8F36160018 for ; Thu, 26 Jan 2023 21:04:11 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=linux.org.uk header.s=zeniv-20220401 header.b=gaFXxUy4; spf=none (imf08.hostedemail.com: domain of viro@ftp.linux.org.uk has no SPF policy when checking 62.89.141.173) smtp.mailfrom=viro@ftp.linux.org.uk; dmarc=pass (policy=none) header.from=zeniv.linux.org.uk ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1674767051; h=from:from:sender:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=WeRZ4ev+cIGFoILzVACqwJK5TvQKgnTXms3rSxBm3Os=; b=bzJGG1n/LIw9hbKX5Vg3NcmdAMn8jZF3512LiEA667dAbeNj4sZ6lbcwl0i1FM8gReKsph uxaeC+JwiFEqnTwLhVGxHm8UxoOMb/GZtp8TUDZkLmB5/KuBqWxGAuD1XncjU95xD1LBn8 BV57lnBL8h2sN7laPJFTU0tO/fLJnlk= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=linux.org.uk header.s=zeniv-20220401 header.b=gaFXxUy4; spf=none (imf08.hostedemail.com: domain of viro@ftp.linux.org.uk has no SPF policy when checking 62.89.141.173) smtp.mailfrom=viro@ftp.linux.org.uk; dmarc=pass (policy=none) header.from=zeniv.linux.org.uk ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1674767051; a=rsa-sha256; cv=none; b=pLmRx2702S/0YBXw94zNOXk4F622S+9V0mvj968t5SOZoayr/qixWAepqZa/sIXIqx5XBt 8AYrFdw6xANL/X253J7Qxg7Of8Brqk2BYOZ1IdGT7T2A1I8QptDNrpKC3egNTpwTWULnjK yGNttPfMx7pnXWpbe8QoeUyX7AV3dDg= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=WeRZ4ev+cIGFoILzVACqwJK5TvQKgnTXms3rSxBm3Os=; b=gaFXxUy4EjaUAeZyDva/yElV0p EdaUMqOQuigNnv2xq2EpY3x0UyDUKjdgg2z1a9pRPnsm71tbWAPoZW6bL6Ykk39km9W4NlFi8eksG KXkHWwCZU9oXcPqf9ITvd4q5mW8n9Fa2pUSMIh5Oai9u+PSj2xDM2KCyac0RxDwqTMv7kNJ3Hq4ky JL0tkytMJqTGe6xnT1nzlwzdwJB3QEChMsl+qsY+4k8lJqwbg5So3V205ymTt3rU/gzAlIiigQZ+C Zclh77KN2yor68DomCPTgk6ES39rDQv38K22daEzWiNBZ+iLs4hJW4sKI0rLtUZPlYzwejkeq/qdL FI0qfqCQ==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1pL9Pe-004JgM-32; Thu, 26 Jan 2023 21:04:03 +0000 Date: Thu, 26 Jan 2023 21:04:02 +0000 From: Al Viro To: Matthew Wilcox Cc: Andrew Morton , "Fabio M. De Francesco" , Ira Weiny , Sebastian Andrzej Siewior , Alexander Potapenko , Andrey Konovalov , Tony Luck , Bagas Sanjaya , David Sterba , Kees Cook , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Thomas Gleixner , Helge Deller Subject: Re: [PATCH] mm/highmem: Align-down to page the address for kunmap_flush_on_unmap() Message-ID: References: <20230126143346.12086-1-fmdefrancesco@gmail.com> <20230126123858.42d9377ad6e352a58c81668b@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: A8F36160018 X-Stat-Signature: wfenxhbf5fud9gkhhmfinqjadimo7j37 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1674767051-199526 X-HE-Meta: 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 azj79nF5 cfhxU72r0M/rkdRxOjdZKiYr7eZ7hX0MRZa01K9mEf41hFSdYQavm7GICc4OAKV+aIlX5z9fXWZ1/um8GU4kiTZQ0fZyS+zflAy+JMv/hcHF8a8M8+s3hljYStH4ZLarIiv+rUSI+8HK6Lfcb8G+phWXhdK7cPqkd4OxTw4Dcja+bh5Ni5nOY5lTPNrANDftWVGzqz/PQE5MIY1piiYaNRRdK+5ZL3Owy8hG4d7RyUhjn31kd8VDa5slEA2tEnd+asT3KOFUbaBIuSfIWBybWqHlGtb002BeTEKQ1aA05y21rPdi6C3SHeKkbdOdnuQew/fPodvzeoOM141bQFwo5ECxarl2kSvmoJuU9uort/54Z1l2/v27ZVprCtUxC5xFqnxbUAX3oO4TUdUfMpOSffQBEcfiFFQHn18I9O9YWIWjKAJwusrOasUDQgg== 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, Jan 26, 2023 at 08:48:03PM +0000, Matthew Wilcox wrote: > On Thu, Jan 26, 2023 at 12:38:58PM -0800, Andrew Morton wrote: > > On Thu, 26 Jan 2023 15:33:46 +0100 "Fabio M. De Francesco" wrote: > > > > > If ARCH_HAS_FLUSH_ON_KUNMAP is defined (PA-RISC case), __kunmap_local() > > > calls kunmap_flush_on_unmap(). The latter currently flushes the wrong > > > address (as confirmed by Matthew Wilcox and Helge Deller). Al Viro > > > proposed to call kunmap_flush_on_unmap() on an aligned-down to page > > > address in order to fix this issue. Consensus has been reached on this > > > solution. > > > > What are the user-visible runtime effects of this flaw? > > The version of this patch I sent out includes this information, > as well as the missed alignment for kunmap_atomic(). One point: AFAICS, the situation right now is * all callers of kunmap_local() pass page-aligned pointers * all callers of kunmap_atomic() seem to do the same * there's nothing in documentation that would say one can pass anything other than the return value of original kmap_local_page() or kmap_atomic() call to those. * there's nothing that would outright ban doing that. So these patches really ought to touch Documentation/mm/highmem.rst saying that from now on kunmap_local() and kunmap_atomic() callers are allowed to pass any pointer within the mapped area. And yes, we want it in -stable before anything that relies upon that sucker gets backported.