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=1793051152; b=tGjXGMmQjsDeWLYjzfsSkSOysJMB/pNGjg4wmlX7sixTDZ/139wGooCANW97ur196D2l XOCfRNMzb/kD9hD9MfDRY6AwYo4S0AZ4+cwqbNr/VHvn43/TU+8Vp1YhtXUKHEKF8BLIa gI+AeWinISrCiYG1FC83Q3WXyZJVlXHos+8yz7xW37+ldai3y6XIU4vy34nXxQmSs+IyW PCK/O6/thtMqlyncZugX0X+PYOGnTLXvzjlGvlpYavo7MJfYgOMvoptu2ic2gLt4OZ2j2 YRZqpFMQJcpUFGyxLloiYmJMg//IvzN5k438p3YMR+cXY205tuhOdAC39eDZtz1lc9w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793051152; h=Received:DKIM-Signature:Date:To:From:Subject:Message-Id; bh=LIxn8dmLwdRcxbqau0966HmEjpdstbqbz/jOXmMb9Yo=; b=TZvrkadaDCqynBwQKgUZQ9IZy7108SQTZ3/5FP9MOW77vTeQ5EEzS3mb7FGSxnupmsty d2tWe1BLOia0uuO12MCqs4qVCgLWvwzdD+ittq0XssbdvKkonZ2roqe4cDHJGrIG0JIPB tY7taYPu2vaZXcz9QfoNlHD8jCLzUyjTFhp0rF2qh9uUgeWn8z5R65rOfJArwHjbRo/Wo Iw2qxK9Ogqh/LNpyzkGHVALSVzgBLEY8fslJ/MJGw/2M50ZBgymuHNdYUv5v6a5JLFcr9 TH58wAjgcC8aqZ2gZyezVJRA4ViphA6IC1NKQJvUH+LBPFf46rEPex6D8cuOENDWRgg== 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=dqVeQbC4; 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 221A3606A31A; Mon, 26 Oct 2026 21:45:51 +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=dqVeQbC4 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8F3311F0128D; Mon, 26 Oct 2026 21:45:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1793051151; bh=LIxn8dmLwdRcxbqau0966HmEjpdstbqbz/jOXmMb9Yo=; h=Date:To:From:Subject; b=dqVeQbC4qIr0XKEoTYc0sRzMppaWWsQ4lfslmU5vODkfafafBD35bSExBo8m45lOr 5E48nR7u228pWNG0GB7+sukWVHH5gmfZeyMDdWY5Kpg3qrBWRT4zXiBWNbJG7Kx8DT MPrg57Pejb/WNwATi+tCF0PMkKozDok0saxZRrTs= Date: Mon, 26 Oct 2026 14:45:51 -0700 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, mike.kravetz@oracle.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: + mm-ksm-fix-userfaultfd-protection-during-merge-and-unmerge.patch added to mm-unstable branch Message-Id: <20261026214551.8F3311F0128D@smtp.kernel.org> X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list The patch titled Subject: mm/ksm: fix userfaultfd protection during merge and unmerge has been added to the -mm mm-unstable branch. Its filename is mm-ksm-fix-userfaultfd-protection-during-merge-and-unmerge.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-ksm-fix-userfaultfd-protection-during-merge-and-unmerge.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ 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) Cc: David Hildenbrand 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: Kiryl Shutsemau 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: Mike Kravetz 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 @@ -4122,8 +4122,11 @@ 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); } @@ -6659,9 +6662,12 @@ 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 mm-ksm-fix-userfaultfd-protection-during-merge-and-unmerge.patch