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imf06.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=MdR85bzh; spf=pass (imf06.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1790077259; b=Y11FNkZvYmNyUe/qYFOHvP/597B83R8ui7T0qEbgOA5s55V0stz3V6ptMeZq3T/Khaz/Zb uyrxy7b53pfIubzhBgT9WRLagI1rC4yLK3YMlm50/c8qwkSp7E/Qy86XxRHYXyblSLWtLp mSdYfTsayBsoXt9GvQMFpfXUAQib5M0= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 0E65F414D0; Tue, 22 Sep 2026 11:40:59 +0000 (UTC) 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 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 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: BC1E1180002 X-Stat-Signature: 8zjaugj8owf8ne418rp9atu8gscbkzaf X-Rspam-User: X-HE-Tag: 1790077259-926689 X-HE-Meta: U2FsdGVkX1874KPWnCU3PCpDoY9E4J43AbV9PsKUdWSaiBlouTX8nUKn8T4jU8JgVqtpVv83wYComKA2BcOpJ8jQx0k57zvIoVtzQ6CMIklTnopi0EAq3U4/mqbFCwImBv6sXbndi5eu3hMHIpBhryzXB7tokxS6Kvsu3/zAaYhkMI6lyPICxe0lHViCEDMAzPntMoZa33cNLYYSFHKfwFZCp2WSKhC1oE/9vNpidfzlodegMIlpbag66ByOeul9iTzip8NCHnt946/Zq+Wa2qNHMpeDKOV8DGuzwZJwtOGV4OEDqgJ5zEq7SMb++1H5g3IImsZp9NwgzPk1haeaIDNoLXnQyxg3vn7UQQRpGGOO9tixYHk9pxC/WDkVxVKOYAPGK/GXuZQpbQDFlHfhYMXvDikdvzikFJRAzyhpryhuHc2/xVY36qUo4k9uRYMZ1nrNfBpXCf9C6szPOIADXGzbakasTXnz6XpIm5fObVxuMIro4L5J/rfwLM03Pm+s1ojxcuGUtKyoa/c+at/EvX8h22LMQ5PqJs/P9PoYp5jJeyFY8Rl/4YVjAi9oWa3qdp+GDyN/6MZOk99oJ5kglq/+YeN+6MeQdLyi+XVFQSS4xQG4AIWtoPJxqLocTvLceBicE3M7iStPWW54/c+8ym4MYmUkUJuj+feuCtAh90QMK52dwJdVxJoI6trj+PUOSwSd2Wcazd+wz+Wxy2miUWQ5Yi/vC5e51JhbGJHrAHcrayFT9UZ7Ft0fqF38adsueIDjbd+ICzPbeQM2owixG8eIdu44yYCWxJHdu0cPIfmiLqezgEDcQ9aJyIT+RS85D4q1cfKc+SL0vuOZ/BlAyunKk08wXkGakwUv3QdY8kz5v2Sjn3FBoxrN37FBApJ+qPng+SBUts9LzpFGRgfg8Y4LSwpeFm68RKcjhUz/CPHtXzrXMnS67KPr3/BbYimqQUkZaLLmwB9jAwPceUV Mt8xVmL1 ksX008KHYjoJPxecbFQcW6KWKKGnfOFqfd2YOSAOyRedSlF2f/nN0JPWU2BLxvG/ZuxCck6XOk9lHrsqzBfyCun1k5ohgfOAnxHyg8+bh0QaJMJJ9XL4h5kNkuLyAv80rqPqX+uSzYdWE8yJ7GlCcVRy1DGadE689ITXVZgrONliFVRE8WBZq2LLM5WEhPr0gS2IVEfNBZsNuNLVU6bIlh66NP5KFz80EdKSttw65nVi2KBTA3AAPcMkschb2gUHL2IVUxGjle5TidCU0thf8nZ3KQY+XW6zrCDXZXVfZ/Gv7rkXwHm/h1/16U69khzcXf3ujeY5BX58f5RU5ji4UwHrW9wh8sJBD8wOK7H35csXybcaOex8+Vj7Nk+OCUjSO05SZMK5n6YZqWBlRQjUD1jXWeh0AiPUvkkG+D/Im9VdVB3Y= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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