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 CABEAEE4996 for ; Tue, 22 Aug 2023 15:24:25 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 12B02280041; Tue, 22 Aug 2023 11:24:25 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0DBD694001B; Tue, 22 Aug 2023 11:24:25 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id EBE10280041; Tue, 22 Aug 2023 11:24:24 -0400 (EDT) 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 DD4CE94001B for ; Tue, 22 Aug 2023 11:24:24 -0400 (EDT) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 9AFC6B1C7B for ; Tue, 22 Aug 2023 15:24:24 +0000 (UTC) X-FDA: 81152112048.20.A44E33D Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf12.hostedemail.com (Postfix) with ESMTP id C9D014000D for ; Tue, 22 Aug 2023 15:24:22 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="M/0/D5T3"; dmarc=none; spf=none (imf12.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1692717863; 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=VmtAtCcHRfR32PnwuVa9rLL2uGT/TuCRRqTlgyU2vBA=; b=A4IxImk6t0PiIHvfUy5Ono5z/PTbD5N1LKIFS3qxBgwaAW9bIJzj9p2eT6tACj+nn3fK5x QVHtVFA3MfD4UyCV/QbzfdRSkrTThRQMpXFseJxkNr7ks80kSttjSqsjuNWlzS80CwwAMd 5MGSlIvRqHFMx6cNpwzIBweP23kGYaQ= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b="M/0/D5T3"; dmarc=none; spf=none (imf12.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1692717863; a=rsa-sha256; cv=none; b=2CpWU/fl9Xy+uaMM5gcUYaS1E/zY4QEg3wkDUYso/s/c5xxGGSIs/6hfF1UFbqMRMOOqfq eOG9WzumBwvUIkNDmbYwjI4qkNDLmrytZCBNWKocRlnc0AN97EVg9Crf+WyRd3COzBE1N5 bbgNf3tdxVcmf3sBoo3EJE0z3hVeRp4= 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=VmtAtCcHRfR32PnwuVa9rLL2uGT/TuCRRqTlgyU2vBA=; b=M/0/D5T3AyM8nE1eiuk7zbB7kQ BJrm5LWDM76wZcpRlUeUCl5ar6M7LqHhjbON3vQMbyweMSxSFmB5OgRYyMzWmBnVFnL7cRXEIRI2k +n31COizrjThN1j9n443LMvLNQLHJUILNsqHPwBiXGmJhYz9WMrndPhu2WLjej9VojPyBazd4IAPZ 3i2zAOqaXLdAgTzgiS0tE8XMBFu5jps70cx4hrqdbETII5iv5evh1/hveF6E8VBdkOPciXOwlGJeA jaQxBw/pZbJCFwqisyevMFsMIrN1oQcerGvlcS3NpR38lQxo3TF10oJ//HmzjywWxjVjY6ifAcgqY VYfbDqvg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qYTDW-00H50z-QD; Tue, 22 Aug 2023 15:22:50 +0000 Date: Tue, 22 Aug 2023 16:22:50 +0100 From: Matthew Wilcox To: Jann Horn Cc: Hugh Dickins , Andrew Morton , Mike Kravetz , Mike Rapoport , "Kirill A. Shutemov" , David Hildenbrand , Suren Baghdasaryan , Qi Zheng , Yang Shi , Mel Gorman , Peter Xu , Peter Zijlstra , Will Deacon , Yu Zhao , Alistair Popple , Ralph Campbell , Ira Weiny , Steven Price , SeongJae Park , Lorenzo Stoakes , Huang Ying , Naoya Horiguchi , Christophe Leroy , Zack Rusin , Jason Gunthorpe , Axel Rasmussen , Anshuman Khandual , Pasha Tatashin , Miaohe Lin , Minchan Kim , Christoph Hellwig , Song Liu , Thomas Hellstrom , Russell King , "David S. Miller" , Michael Ellerman , "Aneesh Kumar K.V" , Heiko Carstens , Christian Borntraeger , Claudio Imbrenda , Alexander Gordeev , Gerald Schaefer , Vasily Gorbik , Vishal Moola , Vlastimil Babka , Zi Yan , Zach O'Keefe , Linux ARM , sparclinux@vger.kernel.org, linuxppc-dev , linux-s390 , kernel list , Linux-MM Subject: Re: [PATCH mm-unstable] mm/khugepaged: fix collapse_pte_mapped_thp() versus uffd Message-ID: References: <4d31abf5-56c0-9f3d-d12f-c9317936691@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: C9D014000D X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: jr1539nmo5knjb1t4gzc6rmjbkshnyx5 X-HE-Tag: 1692717862-376427 X-HE-Meta: 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 y0jhJnsb 7xBdok+KuAyQ1EjzDtVF+x+yiQuksPjNKxKXUCbgUkPFK+vfA5FCyw4cUjLem3RBSNOIC8JSnJuztckd+UF6cGiAoky6Jkimsphe913/1Aq909lIfckCJe4i0P7CiF87FMnFTQFkhr11zgZ1dFJNwWjeyFlINigE+dmK+ul/R5jkXmtl3WnidQOVjz1IhuC8N/TShjCYa0ROicYefxAuJIywAXxGQSrrDqF9tBd0LA9sz/gcUjIJ2w+zsfw6udt2EG0mo 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 Tue, Aug 22, 2023 at 04:39:43PM +0200, Jann Horn wrote: > > Perhaps something else will want that same behaviour in future (it's > > tempting, but difficult to guarantee correctness); for now, it is just > > userfaultfd (but by saying "_armed" rather than "_missing", I'm half- > > expecting uffd to add more such exceptional modes in future). > > Hm, yeah, sounds okay. (I guess we'd also run into this if we ever > wanted to make it possible to reliably install PTE markers with > madvise() or something like that, which might be nice for allowing > userspace to create guard pages without unnecessary extra VMAs...) I don't know what a userspace API for this would look like, but I have a dream of creating guard VMAs which only live in the maple tree and don't require the allocation of a struct VMA. Use some magic reserved pointer value like XA_ZERO_ENTRY to represent them ... seems more robust than putting a PTE marker in the page tables?