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 48753C54EAA for ; Thu, 26 Jan 2023 22:17:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AE0AF8E0005; Thu, 26 Jan 2023 17:17:50 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A91008E0001; Thu, 26 Jan 2023 17:17:50 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9595C8E0005; Thu, 26 Jan 2023 17:17:50 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 83BFC8E0001 for ; Thu, 26 Jan 2023 17:17:50 -0500 (EST) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 522C680F0A for ; Thu, 26 Jan 2023 22:17:50 +0000 (UTC) X-FDA: 80398363500.12.535AF86 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) by imf06.hostedemail.com (Postfix) with ESMTP id A5F22180015 for ; Thu, 26 Jan 2023 22:17:48 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=linux.org.uk header.s=zeniv-20220401 header.b=jQxxxyXc; spf=none (imf06.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=1674771468; 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=RpR41kvGYjpBYQtXapQ3XU33vxpfaI0JWc3v8JbFCC4=; b=kq/AvGZGXQcr7fk1ojoxFlaNUcLGSB0h46SDOhnN+szkCm++S3Le/gkF8Kw9AAEP+WM7hq GTBryK+lDH7Z3Z05GR6HqrY3h1gFI1IABx9vhgOTgNn3KrQKEa0/BKGiOI8JfX748lrNjR 7u+BPvOu/i4F1J4qemJ8O2oAcBjWNIc= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=linux.org.uk header.s=zeniv-20220401 header.b=jQxxxyXc; spf=none (imf06.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=1674771468; a=rsa-sha256; cv=none; b=pqbeCbfeHeF02z3ZHTQRJkMKqDGhZRigryWV3o1QfHN76DLDCBNtUVZQfk6VETx+wTbp0p haO2wtkb5bAZsEU8BZk3vosSuQmatvzqpUrbpJo68/gar0Qtqgq/oyGw/Rg1VfsQpePnpj wB2pLQtqq+yvkQ6x/h/dJBucbaWmRZM= 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=RpR41kvGYjpBYQtXapQ3XU33vxpfaI0JWc3v8JbFCC4=; b=jQxxxyXcoOryVWvJ7Mq7djXSeP 0e3o16zTP8W0dWtfz0/JURhq+rVHc8PjVqaomETP/4eWlRXnv5x9wdHe/N1SHJto1iUfZxtS6afX5 moAVvqAPfsWp2t2vuijclvAjQb3WeWcrJk9AlXIZOFTC3CzJJoD0E4DBcJ00wkCBConYxQlEMrmq6 4uFHepBcsa6xJ+PZCROdsLbumw6VayCGv9ErJl+wArTKlgrYlPizVLikllJBH2LhC7VCWW6IQd3Mi V8D4Z0YPBc7j/BGCGi7lecZPwTSMlmuKGVCzHJnPP/HgLI2tqL5wUqwZ/Np+GOeTsA9WzviEQGp97 XYWyANTA==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.96 #2 (Red Hat Linux)) id 1pLAYn-004KHr-0d; Thu, 26 Jan 2023 22:17:33 +0000 Date: Thu, 26 Jan 2023 22:17:33 +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-Server: rspam07 X-Rspamd-Queue-Id: A5F22180015 X-Rspam-User: X-Stat-Signature: wx46irk6mk88kwzbhyadqfe4or6d8rg4 X-HE-Tag: 1674771468-872492 X-HE-Meta: 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 XjbIiPOM OXvobwRGC1OW/OFUGiCGU9xVlEDO5VcTQEo0CkloJSGRYtKkkneTTqRHJNxG44ROvuQENedZAczInKTn2DnOKXLZhlPJkXD8iBpMJ59qs1Gk81gTAQ0+WyB4+NJcNC9pn5Rk6Sp1yzGjTZLtHfUgNpQwMEQv91hmQsNe28u7uu2gudT3fxKJnD0Jv6Yr3HR7zMg2lZs35oRsACsoCgY+Lfk3Nmu5oRoGe9L9hMqEvIDa8BDA544QFKD4tJE/lzI0Zolv2H1JpK3WeDh7/6w9zirivsnK/g4hIMFEWQJWW+Nlbkzq+MVlGpOc1iKix6vyO+LFra1aIph+thaQYLmg+AS30FrCJfRHD6dqQdwDJ6gu6G/jzM3RVLSRSP2J3Shij49e1kRhRniyKo7E2qBhPs1ObMKPAHAFY6eUaj6m5krutTrFjHqZ7kSRSfA== 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 09:56:07PM +0000, Matthew Wilcox wrote: > On Thu, Jan 26, 2023 at 09:04:02PM +0000, Al Viro wrote: > > 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 > > Ah, no. kmap_local_folio() accepts a byte offset within the folio > and returns a pointer to that byte. I hadn't noticed the parisc > case and thought it was already allowed to pass a misaligned pointer > to kunmap_local() since it is allowed for the highmem case. It > simplified the callers, so it looked like a good tradeoff. > > See, eg 338f379cf7c2: > > - src_addr = kmap_atomic(src_page); > - dest_addr = kmap_atomic(dest_page); > + src_addr = kmap_local_folio(src_folio, > + offset_in_folio(src_folio, srcoff)); > + dst_addr = kmap_local_folio(dst_folio, > + offset_in_folio(dst_folio, dstoff)); > > - if (memcmp(src_addr + src_poff, dest_addr + dest_poff, cmp_len)) > + if (memcmp(src_addr, dst_addr, cmp_len)) > > - kunmap_atomic(dest_addr); > - kunmap_atomic(src_addr); > + kunmap_local(dst_addr); > + kunmap_local(src_addr); Argh... Missed that. OK, then Fixes: on the patch makes a lot of sense. And it still needs a chunk in D/m/highmem.rst...