From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793672147; b=WatryqmN7pqR2zJhKf1jn6/+p5TCZyr3BCIfGokQwZpkpcRLvzOjweKyWqQq4SmqWuKw Qn5+cZDF3MJSb6NlElBoaR3OyT2gBKWqk9uLf909/2xkcq9eK339NlZAe+kAUxNXKl3rT as93KgY96dVOlDhlNn/9XW8invfPSZKvuyrTkLlVO4YwlNtDexvJntnTSvszK06CadUwQ KsY/SF3lwXCz9TindBM8ERhLb6WSic0zYQI1UNPpPw3AsE6OdfbepR+0M95KToZ51DcGc fVy1yKIjHcwC15aDO/up0Fb9O9CWo1BFg0Ok47Dg9FUtu+MKYEt0cZ176BdFT97BD6w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793672147; h=Received:DKIM-Signature:Date:To:From:Subject:Message-Id; bh=APoOSE3eQiTpI/a8/7eMeTk/q6sS/mBd5YfCvBguydo=; b=HmPJAWR3wDdwRAAGgXNR1b0+3m42uaD+D2DXgoMWQwyZ6hrZnM5Tq9G24P3CeLwXKtop fcJZVif1h/Chl8K2WlFBee7/8BMKDY7lvzdS+SW/Vg4Dpa+TcHcn0WORo9TAmmIyTl4lv J20UQoWJtLUWKi11FQnNohnKJdAzdWjFsVP4wLpyIHeMVG21clqMEm4v/bqEBbzBlAjZF OPI0CEY3ZHA3b1lfuW9LCxDxzpDcvvq3etd0klZVv59vaL0rPgGWAxzAo9p5dZF2U6JLk pAiIummi5MO9KfsJUmusVmmWSDzGiogV12lUZBGD24kljNMlj0h5GUHDbiIw/OTo/YQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=rL7fMwcq; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BC2B3606A32E; Tue, 3 Nov 2026 02:15:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=rL7fMwcq Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7D8B81F000C1; Tue, 3 Nov 2026 02:15:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1793672146; bh=APoOSE3eQiTpI/a8/7eMeTk/q6sS/mBd5YfCvBguydo=; h=Date:To:From:Subject; b=rL7fMwcqn+ckPFbur97k19MzPOh9wBs5FNbqbx1l0RgHKrT+wS7mbhvHRBlljbSTH eQ0p/CAoPKZtd2pPhD1Q8b7mn5xdAAGZNe65rLpNSVy6yNViDyr+uJ/HqWRTyBfHcd eYpjAQdh6cHj8tvej35qP2Ikz15R14xXt5hUlcPU= Date: Mon, 02 Nov 2026 18:15:46 -0800 To: mm-commits@vger.kernel.org,ziy@nvidia.com,xu.xin@linux.dev, xemul@openvz.org,vbabka@kernel.org,surenb@google.com,stable@vger.kernel.org, sj@kernel.org,shli@fb.com,seanjc@google.com,samarth.colleges@gmail.com, rppt@kernel.org,riel@surriel.com,peterx@redhat.com,pbonzini@redhat.com, mhocko@suse.com,mgorman@techsingularity.net,med08elkadiri@gmail.com, mcfadden8@llnl.gov,ljs@kernel.org,liam@infradead.org,kas@kernel.org, jthoughton@google.com,jglisse@redhat.com,hughd@google.com,hannes@cmpxchg.org, gokhale2@llnl.gov,dplotnikov@virtuozzo.com,dgilbert@interlog.com, david@kernel.org,cracauer@cons.org,corbet@lwn.net,chengming.zhou@linux.dev, bobbypowers@gmail.com,bgeffon@google.com,aarcange@redhat.com, lance.yang@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-hotfixes-stable] mm-ksm-fix-userfaultfd-protection-during-merge-and-unmerge.patch removed from -mm tree Message-Id: <20261103021546.7D8B81F000C1@smtp.kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list The quilt patch titled Subject: mm/ksm: fix userfaultfd protection during merge and unmerge has been removed from the -mm tree. Its filename was mm-ksm-fix-userfaultfd-protection-during-merge-and-unmerge.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Lance Yang Subject: mm/ksm: fix userfaultfd protection during merge and unmerge Date: Mon, 26 Oct 2026 21:00:54 +0800 KSM loses userfaultfd protection when replace_page() builds a new PTE from vma->vm_page_prot. Dropping its uffd bit lets a subsequent write go through ordinary COW instead of userfaultfd write protection handling. For RWP, a merged page also becomes readable without faulting. Keeping the uffd bit and restoring PAGE_NONE fixes merging, but we also have to handle unmerging. An existing KSM page can be protected with RWP before MADV_UNMERGEABLE, so unmerging already needs fixing independently of preserving RWP during merging. Unsharing replaces a shared page with a private one and should leave userfaultfd protection in place, as do_wp_page() already does for write protection. Currently, an unshare fault reaches do_uffd_rwp() before it can proceed to do_wp_page(). - With synchronous RWP, handle_userfault() returns VM_FAULT_SIGBUS. break_ksm() then reports success with a KSM page still merged. - With asynchronous RWP, protection is cleared before unsharing. Preserve the uffd bit when merging, and restore PAGE_NONE for RWP. Let FAULT_FLAG_UNSHARE skip RWP fault handling and keep PAGE_NONE on each private copy as well. Unsharing can then complete with RWP still armed for a subsequent access. Link: https://lore.kernel.org/20261026130054.91461-1-lance.yang@linux.dev Link: https://lore.kernel.org/all/20261019010934.697895-1-samarth.colleges@gmail.com/ Link: https://lore.kernel.org/all/20261020055518.36087-1-lance.yang@linux.dev/ Fixes: 63b2d4174c4a ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl") Fixes: 2d427bb01639 ("mm/userfaultfd: add RWP fault delivery and expose UFFDIO_REGISTER_MODE_RWP") Signed-off-by: Samarth Narang Signed-off-by: Lance Yang Signed-off-by: Andrew Morton Co-developed-by: Samarth Narang Acked-by: Lorenzo Stoakes (ARM) Reviewed-by: Kiryl Shutsemau (Meta) Acked-by: David Hildenbrand (Arm) Cc: Mel Gorman Cc: Xu Xin " Cc: Chengming Zhou Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Jérôme Glisse Cc: Andrea Arcangeli Cc: Peter Xu Cc: Bobby Powers Cc: Brian Geffon Cc: Denis Plotnikov Cc: Doug Gilbert Cc: Hugh Dickins Cc: Johannes Weiner Cc: Martin Cracauer Cc: Marty McFadden Cc: Maya Gokhale Cc: Pavel Emelyanov Cc: Rik van Riel Cc: Shaohua Li Cc: James Houghton Cc: Jonathan Corbet Cc: Paolo Bonzini Cc: Sean Christopherson Cc: SJ Park Cc: Zi Yan Cc: Mohammed EL Kadiri Cc: --- mm/ksm.c | 8 +++++++- mm/memory.c | 14 ++++++++++---- 2 files changed, 17 insertions(+), 5 deletions(-) --- a/mm/ksm.c~mm-ksm-fix-userfaultfd-protection-during-merge-and-unmerge +++ a/mm/ksm.c @@ -34,6 +34,7 @@ #include #include #include +#include #include #include #include @@ -1463,9 +1464,14 @@ static int replace_page(struct vm_area_s dec_mm_counter(mm, MM_ANONPAGES); } - /* Preserve soft-dirty when replacing the page. */ + /* Preserve soft-dirty and uffd protection when replacing the page. */ if (pte_soft_dirty(orig_pte)) newpte = pte_mksoft_dirty(newpte); + if (pte_uffd(orig_pte)) { + newpte = pte_mkuffd(newpte); + if (userfaultfd_rwp(vma)) + newpte = pte_modify(newpte, PAGE_NONE); + } flush_cache_page(vma, addr, pte_pfn(ptep_get(ptep))); /* --- a/mm/memory.c~mm-ksm-fix-userfaultfd-protection-during-merge-and-unmerge +++ a/mm/memory.c @@ -4125,8 +4125,11 @@ static vm_fault_t wp_page_copy(struct vm if (unlikely(unshare)) { if (pte_soft_dirty(vmf->orig_pte)) entry = pte_mksoft_dirty(entry); - if (pte_uffd(vmf->orig_pte)) + if (pte_uffd(vmf->orig_pte)) { entry = pte_mkuffd(entry); + if (userfaultfd_rwp(vma)) + entry = pte_modify(entry, PAGE_NONE); + } } else { entry = maybe_mkwrite(pte_mkdirty(entry), vma); } @@ -6662,9 +6665,12 @@ static vm_fault_t handle_pte_fault(struc * VM_UFFD_RWP VMA, a protnone PTE without the uffd bit is * NUMA hinting and must still fall through to do_numa_page(). */ - if (userfaultfd_pte_rwp(vmf->vma, vmf->orig_pte)) - return do_uffd_rwp(vmf); - return do_numa_page(vmf); + if (userfaultfd_pte_rwp(vmf->vma, vmf->orig_pte)) { + if (!(vmf->flags & FAULT_FLAG_UNSHARE)) + return do_uffd_rwp(vmf); + } else { + return do_numa_page(vmf); + } } spin_lock(vmf->ptl); _ Patches currently in -mm which might be from lance.yang@linux.dev are