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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C489AFF8873 for ; Thu, 30 Apr 2026 16:53:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3CAC16B008C; Thu, 30 Apr 2026 12:53:10 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3A3446B0092; Thu, 30 Apr 2026 12:53:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 291B86B0093; Thu, 30 Apr 2026 12:53:10 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 139556B008C for ; Thu, 30 Apr 2026 12:53:10 -0400 (EDT) Received: from smtpin28.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 899001C1257 for ; Thu, 30 Apr 2026 16:46:40 +0000 (UTC) X-FDA: 84715800960.28.FA5D275 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf03.hostedemail.com (Postfix) with ESMTP id 3803F2000B for ; Thu, 30 Apr 2026 16:46:37 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=azAn6L1i; spf=pass (imf03.hostedemail.com: domain of kas@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=kas@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1777567598; 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=I8h8kKTkdN7z1XElsH3DVSdti59JiDyE6T9Anf8bntU=; b=otnaQ5uS+YFtJHbTMBWoqEP2ioliSi+AS32YC8nHBoNLvzVqS4SBham4V+1HWrHAkVEhPy GuSvLKpCXZRjN29XvS+PWhyQXFvVk+Y/wWPxMk4FsSUnc6IKg2QReCUs3MuCKWUPciqfu2 rPStvC6juLK0E/rxATZ/4XymomV4EjY= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=azAn6L1i; spf=pass (imf03.hostedemail.com: domain of kas@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=kas@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1777567598; a=rsa-sha256; cv=none; b=VBqCEMjxxSy3hoi+xjRnzKtM42kez2RlJz3/cTlRA4dkllYQu0cXhsfSzk2tnA1td2cMnF fYryT/ejP5LPT4DIZ6d3S9Tf8fKk4EKYyA6nist22bLCAleamEqCW3dOf7+VD1rTeQaW3t SGF3yBTM8QK+gxpiTmwcqED3aET5rmM= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 133A143A53; Thu, 30 Apr 2026 16:46:37 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C6BCC4AF09; Thu, 30 Apr 2026 16:46:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777567597; bh=ee0AbLojRbTTk/miCV2NuwgchMwICYZkqYau2Z3hA7Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=azAn6L1iUdNMjBR/nMIlbjAMC4T4JXjm7euIYiwupXzXoD+p1UNnLQNbMY1iTrwCi 8ncpAGo7ngDftJtz7P+7whwhqBWoVOPN0330D/MK7mBuNLKVHHYy2XEUXdHFdsvYK8 v4MDa+x41RTR1f8gD/Ek31EjHbpMxrZ67Uyhr+Ls1KVgkZApqXjIaMSyiIleLjWBFW 7G6C5GoFa8segxTvPDZ9gVgulrNqld/RlCKpEYEsG84SFXui/KGD4CzFuRieNjtxmf CwvwWHhAtcCAFhUfgSS+LsyyPZwaIT0bF3YdjoxfINm61a+xBlcKdB+NIs9t+3lmcZ U1wpLgZxH11Mw== Received: from phl-compute-05.internal (phl-compute-05.internal [10.202.2.45]) by mailfauth.phl.internal (Postfix) with ESMTP id 8CE60F40077; Thu, 30 Apr 2026 12:46:35 -0400 (EDT) Received: from phl-frontend-03 ([10.202.2.162]) by phl-compute-05.internal (MEProxy); Thu, 30 Apr 2026 12:46:35 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefhedrtddtgdekjeekgecutefuodetggdotefrod ftvfcurfhrohhfihhlvgemucfhrghsthforghilhdpuffrtefokffrpgfnqfghnecuuegr ihhlohhuthemuceftddtnecunecujfgurhepfffhvfevuffkfhggtggujgesthdtredttd dtvdenucfhrhhomhepmfhirhihlhcuufhhuhhtshgvmhgruhcuoehkrghssehkvghrnhgv lhdrohhrgheqnecuggftrfgrthhtvghrnhepgeetuedtjefhkeeuiefgudduvdfgvdeiue eigeehheehudetuedtkeelhfeihedunecuffhomhgrihhnpehsrghshhhikhhordguvghv necuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepkhhirh hilhhlodhmvghsmhhtphgruhhthhhpvghrshhonhgrlhhithihqdduieduudeivdeiheeh qddvkeeggeegjedvkedqkhgrsheppehkvghrnhgvlhdrohhrghesshhhuhhtvghmohhvrd hnrghmvgdpnhgspghrtghpthhtohepgeeipdhmohguvgepshhmthhpohhuthdprhgtphht thhopegrkhhpmheslhhinhhugidqfhhouhhnuggrthhiohhnrdhorhhgpdhrtghpthhtoh eprhhpphhtsehkvghrnhgvlhdrohhrghdprhgtphhtthhopehpvghtvghrgiesrhgvughh rghtrdgtohhmpdhrtghpthhtohepuggrvhhiugeskhgvrhhnvghlrdhorhhgpdhrtghpth htoheplhhjsheskhgvrhhnvghlrdhorhhgpdhrtghpthhtohepshhurhgvnhgssehgohho ghhlvgdrtghomhdprhgtphhtthhopehvsggrsghkrgeskhgvrhhnvghlrdhorhhgpdhrtg hpthhtoheplhhirghmrdhhohiflhgvthhtsehorhgrtghlvgdrtghomhdprhgtphhtthho peiiihihsehnvhhiughirgdrtghomh X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 30 Apr 2026 12:46:34 -0400 (EDT) Date: Thu, 30 Apr 2026 17:46:33 +0100 From: Kiryl Shutsemau To: akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com, david@kernel.org Cc: ljs@kernel.org, surenb@google.com, vbabka@kernel.org, Liam.Howlett@oracle.com, ziy@nvidia.com, corbet@lwn.net, skhan@linuxfoundation.org, seanjc@google.com, pbonzini@redhat.com, jthoughton@google.com, aarcange@redhat.com, sj@kernel.org, usama.arif@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH 08/14] userfaultfd: add UFFDIO_REGISTER_MODE_RWP and UFFDIO_RWPROTECT plumbing Message-ID: References: <20260427114607.4068647-1-kas@kernel.org> <20260427114607.4068647-9-kas@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260427114607.4068647-9-kas@kernel.org> X-Stat-Signature: u3zrphrt4ibinozu41fo4bey961iszbc X-Rspamd-Queue-Id: 3803F2000B X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1777567597-771970 X-HE-Meta: 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 zMZGbIFO rPe7kmlM/aLAI5dk1cxBsBbIW02u+jG06bK1BqG89u9+Y5FvRQCLufdWmhQUxJSBlvkQ63p0xTA076PeCaCjhFGORlSkqkQIVaW/tx08I3fzm090Pph8MZkJ4adUAXb9tN836HqTZ91D2GnpTA+LMVnx3aE+DjtVvD/KMKeo4Zj0PyKeZLFphkWkbpOZ/imPm+Znl9QCQbmV60HU8rElHDIHLqtQUNMTWkVI1HWmn/AZQCNOH6KA3e8yOZWh2M9xAxlMEZCeLZQQCBxFmxXtIN2lGoIO/hrQLXLF5SYbcqV2V25fabV46Zwlk5cUxvcQhrXgB6WCtOHsmiUnaZxKbqOQFyBH36DckjROGoAzFaUm3Yeb7xroluSYPZ+kUx+mrMmW8k9Byy2yyvi2e5Jn8O+dphg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: sashiko.dev -- https://sashiko.dev/#/patchset/20260427114607.4068647-1-kas@kernel.org -- wrote: > + if (enable_rwp) > + mm_cp_flags = MM_CP_UFFD_RWP; > + else > + mm_cp_flags = MM_CP_UFFD_RWP_RESOLVE | MM_CP_TRY_CHANGE_WRITABLE; > > Does this unconditionally apply MM_CP_TRY_CHANGE_WRITABLE to the entire range? Confirmed bug. RWP registration does not require VM_WRITE, so mmap(PROT_READ) UFFDIO_REGISTER(MODE_RWP) UFFDIO_RWPROTECT(, disable) trips WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE)) inside maybe_change_pte_writable() on resolve. The flag belongs inside the iteration, gated on vma_wants_manual_pte_write_upgrade(vma), matching mwriteprotect_range() (mm/userfaultfd.c:1003) and userfaultfd_clear_vma() (mm/userfaultfd.c:2182): for_each_vma_range(vmi, dst_vma, end) { unsigned long vma_start = max(dst_vma->vm_start, start); unsigned long vma_end = min(dst_vma->vm_end, end); unsigned int flags = mm_cp_flags; if (!enable_rwp && vma_wants_manual_pte_write_upgrade(dst_vma)) flags |= MM_CP_TRY_CHANGE_WRITABLE; change_protection(&tlb, dst_vma, vma_start, vma_end, flags); } Will fold for v2. > Since change_protection() walks and modifies page tables here, does this > need to call vma_start_write(vma) first? No. This is the same locking pattern as the pre-existing uffd_wp_range() call that the hunk replaces -- mmap_write_lock without vma_start_write(), which remains safe for the same reasons: - mmap_write_lock excludes anything taking mmap_read_lock, including MADV_DONTNEED and the other PTE-page-freeing paths (try_to_free_pte() runs under mmap_read_lock + per-VMA locking, never standalone). - The remaining concurrent reader is the per-VMA-locked page fault (lock_vma_under_rcu()), which walks PTEs under the PTE lock. change_protection() also takes the PTE lock when updating, so the two serialise. A fault that observes a transient pre-resolve PTE just produces a normal fault delivery and resolves correctly. -- Kiryl Shutsemau / Kirill A. Shutemov