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 F26D7C433FE for ; Wed, 19 Jan 2022 18:01:44 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 8D2AB6B0071; Wed, 19 Jan 2022 13:01:44 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 85BF56B0072; Wed, 19 Jan 2022 13:01:44 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6FDA66B0074; Wed, 19 Jan 2022 13:01:44 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0150.hostedemail.com [216.40.44.150]) by kanga.kvack.org (Postfix) with ESMTP id 60CCB6B0071 for ; Wed, 19 Jan 2022 13:01:44 -0500 (EST) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 26BCD812538B for ; Wed, 19 Jan 2022 18:01:44 +0000 (UTC) X-FDA: 79047804528.28.195C4D8 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf01.hostedemail.com (Postfix) with ESMTP id 9734C4000E for ; Wed, 19 Jan 2022 18:01:43 +0000 (UTC) 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=wl35Nv5bzMCc708L4TqlyxLqxeH3mVDxX3k5zPuEGYo=; b=e6nKWnC2p+Tf/OuPB41XZewJTw 9aR5M2y6V/hfTahSIhFlgmKQoZ3OddEQoQb9TKA0jXQ2gbJRF6D0r6+TfbLm/heQJSprsV/QYpqcY qq11o1p/4VBTmIwr4vC84NqqRk0geKSmNkyOUY69cPTWm88tcFDEhTdqyUm7MD1Lbct50fNlKC99a BsyYPEPzDplXfd6VxNXD1dTJDfwfytPkKD8GZO/CVy0HjvUTo6ESV0VgcPXaG/+fAuvU5U+FtEZze H0KgRLdO8+qm8+U5XG8DSeVKCdBYV9XUUZv9SK820h3R+8x+V0sT9bzgLLNLmFZSPNdd5Lmkzn0+L h7HcSL4g==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1nAFGu-00BeGf-9X; Wed, 19 Jan 2022 18:01:24 +0000 Date: Wed, 19 Jan 2022 18:01:24 +0000 From: Matthew Wilcox To: "Russell King (Oracle)" Cc: Robin Murphy , Yury Norov , Catalin Marinas , Will Deacon , Andrew Morton , Nicholas Piggin , Ding Tianhong , Anshuman Khandual , Alexey Klimov , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] vmap(): don't allow invalid pages Message-ID: References: <20220118235244.540103-1-yury.norov@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 9734C4000E X-Stat-Signature: hutzyhg3yhzdxkaxxucb5nkti8ae4ixp Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=e6nKWnC2; spf=none (imf01.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none X-HE-Tag: 1642615303-477838 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 Wed, Jan 19, 2022 at 05:54:15PM +0000, Russell King (Oracle) wrote: > On Wed, Jan 19, 2022 at 04:27:32PM +0000, Matthew Wilcox wrote: > > On Wed, Jan 19, 2022 at 01:28:14PM +0000, Robin Murphy wrote: > > > > + if (WARN_ON(!pfn_valid(page_to_pfn(page)))) > > > > > > Is it page_to_pfn() guaranteed to work without blowing up if page is invalid > > > in the first place? Looking at the CONFIG_SPARSEMEM case I'm not sure that's > > > true... > > > > Even if it does blow up, at least it's blowing up here where someone > > can start to debug it, rather than blowing up on first access, where > > we no longer have the invlid struct page pointer. > > > > I don't think we have a 'page_valid' function which will tell us whether > > a random pointer is actually a struct page or not. > > Isn't it supposed to be: > > if (!pfn_valid(pfn)) { > handle invalid pfn; > } > > page = pfn_to_page(pfn); > > Anything else - even trying to convert an invalid page back to a pfn, > could well be unreliable (sparsemem or discontigmem). This function is passed an array of pages. We have no way of doing what you propose.