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 6A14ECD5BB1 for ; Fri, 22 May 2026 11:51:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D19656B0093; Fri, 22 May 2026 07:51:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CEF0F6B0095; Fri, 22 May 2026 07:51:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C2D636B0096; Fri, 22 May 2026 07:51:23 -0400 (EDT) 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 B3A186B0093 for ; Fri, 22 May 2026 07:51:23 -0400 (EDT) Received: from smtpin04.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 5F4531619DA for ; Fri, 22 May 2026 11:51:23 +0000 (UTC) X-FDA: 84794890446.04.D2A9161 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf21.hostedemail.com (Postfix) with ESMTP id 735CC1C0004 for ; Fri, 22 May 2026 11:51:21 +0000 (UTC) Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="Wx/KGeJW"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf21.hostedemail.com: domain of kas@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=kas@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1779450681; 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=Mb5pSbbAGYerWjfqxHgQXJ81h4yET5l0OQn5Vn752FE=; b=gvuUkTdDhyI2retN+5wCyjWU6Di4iFYP4+KE/CC5t2PnKNO/hvcnN1fammseP6Bv0v4V4C lTiAoPIOysmRop78Hf4RcWkfibioXUhnFeLOLsW6ZV78LLON+dkdxN2WQ8GuLGYPIZLGqT yN6oWZwB3Ovt3PQkYubf3n6NsNnkCXc= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1779450681; a=rsa-sha256; cv=none; b=g3PwykLw+gCToDOIcHq/p/Kx6YG4Jl0+C61p7L4eB+BXTeh2MK6a79lC5xL9adsbjWSwnj /Y3Nlbb/wtGHS7zIre6JFzHDeGMBQQH1/6OISsgXzSW+SEXEeZWwehzhN4wv5gD2RzbVfZ yAIAez+MiEapYZYjrYcKrpgxZNZOP8g= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="Wx/KGeJW"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf21.hostedemail.com: domain of kas@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=kas@kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id DF64660138 for ; Fri, 22 May 2026 11:51:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 59D051F00A3E; Fri, 22 May 2026 11:51:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779450680; bh=Mb5pSbbAGYerWjfqxHgQXJ81h4yET5l0OQn5Vn752FE=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Wx/KGeJWlF2Zr6qrDmGOviCunxl1pvuPYJEtXPnsRc2sv+cGOfWuDkQYe19P/XgJF DV4ABfqKzI442PvPYQnd9Vmk9AxeGfMHFmWM/Wzl8bYf4qGE0bmWaF5sbfCG/WnhYd kKwiC4iHkWe+3F42VZBVVk6fmGl/kxOdyNplrMsBCf2xgwv3R+QWwmgUlKWMW1wUh6 jBzUqzZU7c/GwdKUhbtdHdjIZMYtAo0Ym4p2oGPJie57LP1Gw3XNGWdxDWYsLrXwLB Lb/gfSY7moaLGg5LTDQFGc2AG1Do73RgBKnbeWLhA9dUVxG7I2UEYsw0EekOxOBVkj IifVwtTpGehhA== Received: from phl-compute-03.internal (phl-compute-03.internal [10.202.2.43]) by mailfauth.phl.internal (Postfix) with ESMTP id AE3E0F40068; Fri, 22 May 2026 07:51:19 -0400 (EDT) Received: from phl-frontend-03 ([10.202.2.162]) by phl-compute-03.internal (MEProxy); Fri, 22 May 2026 07:51:19 -0400 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeefhedrtddtgdduhedttdelucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfurfetoffkrfgpnffqhgenuceu rghilhhouhhtmecufedttdenucenucfjughrpeffhffvvefukfhfgggtuggjsehttdertd dttddvnecuhfhrohhmpefmihhrhihlucfuhhhuthhsvghmrghuuceokhgrsheskhgvrhhn vghlrdhorhhgqeenucggtffrrghtthgvrhhnpeeuieejieffkeehfeffffdtkeelfeelhe fhfefhudehjeehvdffleeuvddufefgkeenucevlhhushhtvghrufhiiigvpedtnecurfgr rhgrmhepmhgrihhlfhhrohhmpehkihhrihhllhdomhgvshhmthhprghuthhhphgvrhhsoh hnrghlihhthidqudeiudduiedvieehhedqvdekgeeggeejvdekqdhkrghspeepkhgvrhhn vghlrdhorhhgsehshhhuthgvmhhovhdrnhgrmhgvpdhnsggprhgtphhtthhopeegiedpmh houggvpehsmhhtphhouhhtpdhrtghpthhtoheprhhpphhtsehkvghrnhgvlhdrohhrghdp rhgtphhtthhopegrkhhpmheslhhinhhugidqfhhouhhnuggrthhiohhnrdhorhhgpdhrtg hpthhtohepphgvthgvrhigsehrvgguhhgrthdrtghomhdprhgtphhtthhopegurghvihgu sehkvghrnhgvlhdrohhrghdprhgtphhtthhopehljhhssehkvghrnhgvlhdrohhrghdprh gtphhtthhopehsuhhrvghnsgesghhoohhglhgvrdgtohhmpdhrtghpthhtohepvhgsrggs khgrsehkvghrnhgvlhdrohhrghdprhgtphhtthhopehlihgrmhdrhhhofihlvghtthesoh hrrggtlhgvrdgtohhmpdhrtghpthhtohepiihihiesnhhvihguihgrrdgtohhm X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Fri, 22 May 2026 07:51:18 -0400 (EDT) Date: Fri, 22 May 2026 12:51:16 +0100 From: Kiryl Shutsemau To: Mike Rapoport Cc: akpm@linux-foundation.org, peterx@redhat.com, david@kernel.org, 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 v2 09/14] mm/userfaultfd: add RWP fault delivery and expose UFFDIO_REGISTER_MODE_RWP Message-ID: References: <454b3381cb7ead65291b2d7e24c0bff62e55c41b.1778254670.git.kas@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 735CC1C0004 X-Stat-Signature: ekkoncr87kap3ifdx9djnaj1ks1c7swc X-Rspam-User: X-HE-Tag: 1779450681-667006 X-HE-Meta: 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 8+jCwC22 jO6otY5/HHLehqQdNN0vgUL50dRete1rfvG5EKzQxhBja2O7uK3Hr5j3Tvr4qeiv3Rv7YHnKSELrcwRbMUPZ+hjaMzQKiIbchKNdJTOZEWPreYiUvH/GNUivmT94SGT5bxDMBUpGm70coYCrlsf+RLEkBgcdMoEGMazJb99cnSyI2L0C27SUrK5aXGE+1hQ4kmIoSxED5c9Lm3d/MUmKvTvjMXBVpsm1tMCSfR2cmQu9mXzSqduRbn5hT6stioZiVaZ/Ux8oWoPFdLYWhDdtKlEsPnt8rFv2bpTQl5kXB2JDUeUAyp8++kXrK1vWZvbsq8EtAj1DKwAuRsOnTrrMuwpDf0o3mvIhh/em4+X1IY+qnoJHKedFbaakoEuvzH2oTdg+9aP42MGTVMioS2QA91uJsOALYUunr3FN/ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, May 12, 2026 at 08:29:02PM +0300, Mike Rapoport wrote: > On Fri, May 08, 2026 at 04:55:21PM +0100, Kiryl Shutsemau (Meta) wrote: > > Wire the fault side of read-write protection tracking and turn the > > userspace interface on. > > > > An RWP-protected PTE is PAGE_NONE with the uffd bit set. The > > PROT_NONE triggers a fault on any access; the uffd bit distinguishes > > it from plain mprotect(PROT_NONE) or NUMA hinting. > > > > Fault dispatch, per level: > > > > PTE handle_pte_fault() -> do_uffd_rwp() > > PMD __handle_mm_fault() -> do_huge_pmd_uffd_rwp() > > hugetlb hugetlb_fault() -> hugetlb_handle_userfault() > > > > The RWP branches gate on userfaultfd_pte_rwp() / userfaultfd_huge_pmd_rwp() > > (VM_UFFD_RWP plus the uffd bit) and fall through to do_numa_page() / > > do_huge_pmd_numa_page() otherwise. Each delivers a > > UFFD_PAGEFAULT_FLAG_RWP message through handle_userfault(); the handler > > resolves it with UFFDIO_RWPROTECT clearing MODE_RWP. > > > > userfaultfd_must_wait() and userfaultfd_huge_must_wait() add matching > > protnone+uffd waiters so sync-mode fault handlers block correctly. > > > > Expose the UAPI: > > > > UFFDIO_REGISTER_MODE_RWP -> UFFD_API_REGISTER_MODES > > UFFD_FEATURE_RWP -> UFFD_API_FEATURES > > _UFFDIO_RWPROTECT -> UFFD_API_RANGE_IOCTLS > > UFFD_API_RANGE_IOCTLS_BASIC > > > > UFFD_FEATURE_RWP is masked out at UFFDIO_API time when PROT_NONE is > > not available or VM_UFFD_RWP aliases VM_NONE (32-bit), so userspace > > never sees an advertised-but-broken feature. > > > > Works on anonymous, shmem, and hugetlb memory. > > > > Signed-off-by: Kiryl Shutsemau > > Assisted-by: Claude:claude-opus-4-6 > > A small nit below, other than that > > Reviewed-by: Mike Rapoport (Microsoft) Thanks! > > @@ -347,6 +359,14 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx, > > */ > > if (!pte_write(ptent) && (reason & VM_UFFD_WP)) > > goto out; > > + /* > > + * PTE is still RW-protected (protnone with uffd bit), wait for > > + * userspace to resolve. Plain PROT_NONE without the marker is not > > + * an RWP fault. > > + */ > > + if (pte_protnone(ptent) && pte_uffd(ptent) && > > + (reason & VM_UFFD_RWP)) > > Nit: this fits even in 80-chars line Ack. -- Kiryl Shutsemau / Kirill A. Shutemov