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 1CF3C53D0D4; Tue, 22 Sep 2026 11:41:01 +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=1790077270; cv=none; b=O+p/P/9plWTyFz/b0z8oZOJDkgIDvd3TSoIolJ24LseJPmcVDs0L3yYgAmqRAM81NvIfAsVVTgPNWLGNi3Lr4ukeGh0xK103etjW4RaKhaXSos3eOZfZIU97MB/GMfiyaF4Z3bneEFCy6zdR+YEpB7GyKSkl/p1FhZYall7Vyug= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790077270; c=relaxed/simple; bh=jxO2tbCn05NkUfkav108Q3sl+zdNebjag0oxiZ6oa7k=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cQ6pB5Ifk8ftASWZtctNsRALANn1cC0zUfwh+TX0Hb0vnXJocuSqgqc5a3GxgQ2ZI5H3k6KqTT0wXHqcUKiAJFVqbxOLO+IEgtxWDDBzUyprWCltph27sr/+We2tXCfM+sE+RmAmFzZkHEeuaX6A2qL06gbMaqsrr1vQH9y+VGs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MdR85bzh; 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="MdR85bzh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 757891F00898; Tue, 22 Sep 2026 11:40:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790077258; bh=F+/XiWey5CLZx+RgVIraKLoSGfEXc6kJ7NpnMFbxg/g=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=MdR85bzh1RoqepA7zsF3/V8Pl3ctZkZaPAwXAkpWebSOYwMiIbBg3nw2cdV5909Er Uedjv/1PNvNeBmzZVpxsppAHst/XgeDExrGvWwvfJAnxrHh4tAkKsOPgQm6wtCkQfF 6iiKaW9kUgyR0zBRpZOv3kT37aMB6ZltRGaudFj4ZeHkg0ZrOYTxubjYHGxFjhAUDR ZNZPm7Pp828QoHwc6rw+JMG5FdJKk7qkk51QeZdkB8WLdt7TyuAuCd1jWyFrppvasK ctEmDZ+yTGQRmAQOCEs7HRUudU4TKL1rsVIklBs9ms2+yTi5bCf+8tCq8DpcgD6HH8 RnGkReCInrnWg== Message-ID: <49208ed6-6c20-49a9-9c0d-0e1cffe1898f@kernel.org> Date: Tue, 22 Sep 2026 13:40:51 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] userfaultfd: clear the inherited uffd bit in move_swap_pte() To: Donggeun Yoo , akpm@linux-foundation.org, rppt@kernel.org Cc: peterx@redhat.com, surenb@google.com, aarcange@redhat.com, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, mhocko@suse.com, shuah@kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260919004630.1159895-1-donggeunyoo.kernel@gmail.com> <20260919004630.1159895-2-donggeunyoo.kernel@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/19/26 02:46, Donggeun Yoo wrote: > UFFDIO_MOVE on a swapped-out page installs the source PTE at the > destination unchanged, so a uffd bit set on the source lands in a > destination VMA that was never registered for write protection. It is > then permanent: the bit is dropped only by change_protection() under > MM_CP_UFFD_{WP,RWP}_RESOLVE, which uffd_wp_range(), mrwprotect_range() > and userfaultfd_clear_vma() issue only for a VMA registered in that > mode. pagemap reports the page as uffd-tracked, and MADV_COLLAPSE > refuses the range while the bit is set, because collapse_scan_pmd() is > strict about uffd on swap entries. > > move_present_ptes() and move_zeropage_pte() build the destination PTE > from dst_vma->vm_page_prot and arm RWP only when dst_vma asks for it, so > the destination's own registration decides the result. move_swap_pte() > copies the source PTE instead and only ever sets the bit, never clears > it, so one UFFDIO_MOVE behaves differently depending on whether the page > happened to be resident. > > Clear the uffd bit on the moved swap entry unless the destination is > RWP-registered, as copy_nonpresent_pte() does where it installs a PTE > into a destination that may not be armed. A WP-registered destination > stops inheriting the bit as well, which is already what it gets when the > moved page is resident. > > Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") > Cc: > Signed-off-by: Donggeun Yoo > --- > mm/userfaultfd.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 74f04c323c50..6495666c596b 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -1452,6 +1452,8 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, > /* Re-arm RWP on the moved swap entry if dst_vma is RWP-registered. */ > if (userfaultfd_rwp(dst_vma)) > orig_src_pte = pte_swp_mkuffd(orig_src_pte); > + else > + orig_src_pte = pte_swp_clear_uffd(orig_src_pte); > set_pte_at(mm, dst_addr, dst_pte, orig_src_pte); > double_pt_unlock(dst_ptl, src_ptl); > In move_present_ptes() we don't run into that issue as we create a new PTE from scratch orig_dst_pte = folio_mk_pte(src_folio, dst_vma->vm_page_prot); Staring at the if (userfaultfd_rwp(dst_vma)) I do wonder why we don't have to take similar care about wp ... I'm sure the is a good reason. Code change itself LGTM. -- Cheers, David