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 63CF7C54EAA for ; Thu, 26 Jan 2023 21:56:26 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id F0FBC8E0002; Thu, 26 Jan 2023 16:56:25 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id EC05D8E0001; Thu, 26 Jan 2023 16:56:25 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D88B38E0002; Thu, 26 Jan 2023 16:56:25 -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 C98FB8E0001 for ; Thu, 26 Jan 2023 16:56:25 -0500 (EST) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 902031C214B for ; Thu, 26 Jan 2023 21:56:25 +0000 (UTC) X-FDA: 80398309530.17.5A80B1E Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf16.hostedemail.com (Postfix) with ESMTP id 3168F180011 for ; Thu, 26 Jan 2023 21:56:21 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=cjRnJXPG; spf=none (imf16.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1674770183; h=from:from: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=n+wxB0NNSlH+B4h0DWc/6/aSEBfGsI/y4mnQs/HfTU4=; b=2OJZNn7PL5ZhGKPZJM+746Fp29msR9YgzERZXcV8DsCr7vRMKvXvMF/XT01w42p9aLyZwQ tWiZgDGNOd8fEqBC/RUGAIB8SI1O9tRm64pQTkDfzRovwe3Ewq9gtl6CVwKG2HODDyGNLI MR38Jnd8k2zbt76Io9rVKuRNEOjgkug= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=cjRnJXPG; spf=none (imf16.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1674770183; a=rsa-sha256; cv=none; b=x9AN1lYq9iysV8i1rkn0U55GpnltV8j5Q4zngsCjbS3yCkWehQgVmadtpGzNb47qkDuGbc dQTcLLcrBOMDCQjMWij1Vnk6G5baPhl6VhGKvvC3noeyf940loAlgPZmHqHLwO0O3pGO/k hSN7DrUTDTlPxzJghc6bZpB32MGuLUg= 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=n+wxB0NNSlH+B4h0DWc/6/aSEBfGsI/y4mnQs/HfTU4=; b=cjRnJXPGEbVg4snSEKB+FUz7nw 0uHU/qZOlYcBvCBemGLwXFAB0EAsaIkpe1dAGgrZPYfh+68M5SzKqLJzeXTHv3uIGVe0qOFVKdxe1 l5g2xqYfGFOX1LuSDyXPEP4NlXIvRsjWxCPn9NLx82m+eeD9WVARbMGpvkBLRa5vaEuwFsRCkGNDq dS+Zq3rzVyufeAyiyNKAnwhpYoExhnDLwx3l59NlZjEKruFnJaY7IzgOurwksN5brwRALcFL7Sf2U amdeel0Ivx5n9SVtAu0x/eXj23AEuCg6dPSFCobvkjmPQ09BjrTKwU4NFCoCP7kWfz2tiESJg/ylp s56Ywj7w==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pLAE3-0077CA-KU; Thu, 26 Jan 2023 21:56:07 +0000 Date: Thu, 26 Jan 2023 21:56:07 +0000 From: Matthew Wilcox To: Al Viro 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: 3168F180011 X-Rspam-User: X-Stat-Signature: diy5zzeb8pdt1p1mpjsyka6zyekoj4g8 X-HE-Tag: 1674770181-771182 X-HE-Meta: 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 CJ5xnfwf 89Wvyu26D6z+6u9XkYHphKvLXousZR67ZcRciaja+LLfFKorKknibtDAyFRrz23Ryi8J3Fw+oJsHy5bWgmuoMKymcSu01qPob/EEy2qvsfKbnPl8F9NrBrY1u50jLbHg4cPqMhpKmcDbahnGgGw3XIQyn/W4/9HGFGyHBeXDIiNHdyGgymMvEaxGfgovSf48ha1txn78UsUlM/ruqJEas/CoOSGr8LKNI0E34 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 09:04:02PM +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);