From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 172563F44FC; Tue, 25 Aug 2026 11:26:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787657211; cv=none; b=Z24IUTU6vVRpKenIjhbnjZ1ACU26ooe69XfUthIWQweQpB8Sxz1RR9t0dkAY33jnwa/5Ug1Ezog5dSztAmFmhlR9LL7AeWmSLJoSAqTL6XpOOf0xnASa+HtrURCxGXOPJfncjyJYU2fI2K/sIZMV9EdudpFNaWi5C2QIgnQ4EK8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787657211; c=relaxed/simple; bh=PbYB/wvtFM1VPd3iwbL1tVogTkEhGUZQvsMK0I2XnnU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OaF68BEnmxFwaRgxxkyuoxlZ0jQURoQF4NMsuyd+EuEGexBHeecHceZ0M5mXFSMWbRYq6cfaSCCmymFVSUnGaVwgLzwuPDr7vfNK3mh10ZaEmar/kIgjZa1lusQx8goI3wXDQePzCvX5G5Rc4PbGUWABBlXuVzOoTgj6wg2AlG4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GoXlgVdV; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GoXlgVdV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F260C1F000E9; Tue, 25 Aug 2026 11:26:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787657209; bh=+Kwg1vlmpiXfsrVuG+kXUemOecdCeye6XceIRD4GCkc=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=GoXlgVdVnQB3UIKDtlCK2MeqgMCYQLVg5a+xp6sO3+cbWgVd5+A/I2aV1BFeUM7k6 BVHc7H3QnM5OAstm5ICZF1F8UtUkOy4StSrkX8dng+bSYclRRQOkGUeYGNXJIH+4/P l6uMBxScbiacbX2oODUOkqBBoDvwqh6gu0SouefX1HJd802b3VnwzhSPutCafbEAgU 8TdZqHlqFtDqM86XjkQzIPwG4CoL+2UmnlHJLOG1je/70VJB/I7p+JYvsI646XL6a8 Mci0t5DOw3pDjpm/SEMAL6Qcu0JDgf8r4KMhu5L88J2MrpMu0jWyZHq0dsDmDpecvY UJWoV4aI7U0Kg== Date: Tue, 25 Aug 2026 12:26:39 +0100 From: "Lorenzo Stoakes (ARM)" To: Mike Rapoport Cc: Andrew Morton , David Hildenbrand , Baolin Wang , Barry Song , Dev Jain , Hugh Dickins , Jann Horn , Jason Gunthorpe , John Hubbard , Jonathan Corbet , Lance Yang , "Liam R. Howlett" , Masami Hiramatsu , Mathieu Desnoyers , Michal Hocko , Muchun Song , Nico Pache , Oscar Salvador , Pedro Falcato , Peter Xu , Ryan Roberts , Shakeel Butt , Shuah Khan , Steven Rostedt , Suren Baghdasaryan , Usama Arif , Vlastimil Babka , Zi Yan , linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH 3/6] userfaultfd: use userfaultfd_*() helpers instead of open coded flag tests Message-ID: References: <20260823-uffd-vm-flags-v1-v1-0-3086981b33cf@kernel.org> <20260823-uffd-vm-flags-v1-v1-3-3086981b33cf@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Aug 25, 2026 at 02:19:52PM +0300, Mike Rapoport wrote: > > > +/* > > > + * Don't do fault around for WP, RWP or MINOR registered uffd range. For > > > + * MINOR registered range, fault around will be a total disaster and ptes can > > > + * be installed without notifications; for WP it should mostly be fine as long > > > + * as the fault around checks for pte_none() before the installation, however > > > + * to be super safe we just forbid it; for RWP, pre-faulted neighbours would > > > + * be indistinguishable from accessed pages in PAGEMAP_SCAN (PAGE_IS_ACCESSED) > > > + * and pollute the tracked working set, so each page must be populated by its > > > + * own fault. > > > + */ > > > +static inline bool uffd_disable_fault_around(struct vm_area_struct *vma) > > > +{ > > > + return userfaultfd_minor(vma) || userfaultfd_wp(vma) || > > > + userfaultfd_rwp(vma); > > > > This is changing the logic. > > > > Before we were testing only the flags, now we have: > > > > static inline bool userfaultfd_rwp(const struct vm_area_struct *vma) > > { > > /* > > * Callers gate PAGE_NONE usage on this; PAGE_NONE is a BUILD_BUG() > > * without CONFIG_ARCH_HAS_PTE_PROTNONE, so fold to false. > > */ > > if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_PROTNONE)) > > return false; > > return vma_test_single_mask(vma, VMA_UFFD_RWP); > > } > > > > I.e. adding in a CONFIG_ARCH_HAS_PTE_PROTNONE check. > > Without CONFIG_ARCH_HAS_PTE_PROTNONE VMA_UFFD_RWP is hardwired to VM_NONE > so it's functionally the same ;-) Well then you're explicitly removing logic and not mentioning it anywhere with a NFC commit. So please say so in the commit message. > > > BTW side-note these: > > > > static inline bool userfaultfd_missing(const struct vm_area_struct *vma) > > { > > return vma_test_any_mask(vma, VMA_UFFD_MISSING); > > } > > > > static inline bool userfaultfd_wp(const struct vm_area_struct *vma) > > { > > return vma_test_any_mask(vma, VMA_UFFD_WP); > > } > > > > static inline bool userfaultfd_minor(const struct vm_area_struct *vma) > > { > > return vma_test_any_mask(vma, VMA_UFFD_MINOR); > > } > > > > Should all use vma_test_single_mask() really :) > > These are changed anyway in a later patch. Yup, but you (potentially) break one of them. Will comment there. > > > -- > > Cheers, Lorenzo > > -- > Sincerely yours, > Mike. -- Cheers, Lorenzo