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=1794273148; b=bJehH2zMD+Wp0AEYsZq1mkAOsoN6MFxu6FGzi+rek/dhd6ZcPCnpaN4cDBZunjnwgGWZ d8zKOvN1EGutpom3x8kn1eAt0e/nNR37teLGNLRR1qVUmlgXcBoL2WNMN+hx2NrGwNfY8 iT3mubuXi2vTvgiYkKM11a20joy+2wx1blgfeNcFGUkxjkIX5lKEbJUpLHF+bvCfB/XvW VCYLulYgwTE9UJFAFblNHf8zaO7BS+EuAhEMyEFPigK/tyPqEjYYMq6Z8FL2Sxmultktf o7lCcMO7VOZtJEt+dB+ygIhqhNWZWxiJuW02czX0Og93FoCXhQV076qPMJJVW8/rC/A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794273148; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=gq4pLAA9gkk1j2JTrOymGaJlH/2AvXkuCe42cxUT7zM=; b=S3GRHhbwEPHq71yaedA7Vk/sZtfcTHbBf0Kue9vF8LiIPyV1nKl2pgVhESwuK/zb7b9r QX+wvMOerRoB6pvU0etXMq5j5yp4OwwKzf67QXE2DKY/dqnJqZ1o+tWUDt+RrvRWRqdoQ tmqC3SdevKMoi8/x6RDHpp3cW0Jbt7xjoTNUxMnoNKdcY2oUcRm/nMjmqk+JhZYSkd0q+ W5Ig0nANyYdrKblwwRXUgzzMzXvIon+OF/FKUfsNYSTm0b7+BsWo0ldd3RAGWhyYvVCES xmma0Pl0dYY/hT96DL7zFujUfhmOtsBQd2jG9zA4r2iZNLjPHkV3ecl7G6YmuVW8R7A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=LcorPuT+; 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 9C98A606A31C for ; Tue, 10 Nov 2026 01:12:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=LcorPuT+ Received: by smtp.kernel.org (Postfix) with ESMTPSA id C51C71F0089F; Tue, 10 Nov 2026 01:12:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794273147; bh=gq4pLAA9gkk1j2JTrOymGaJlH/2AvXkuCe42cxUT7zM=; h=From:To:Cc:Subject:Date; b=LcorPuT+1zGzUmELrs6B+i3B/83pAIk6OGlIFgIjjfFEVRsP0JnL/DEtcAUnroLJV 6OD04u18T3AMqNz6RvdbNngYfw55F9gVJ3cF7AuNwv3IzUU7b0hQpjKLwFBUsA1nW1 oWVZ2rP4P+ex8w9HB+npgD9yLD0aJ++QDQDwNvriCgldsWOkEa78BHjn6rHbzoCveU 0ZIT/kno6DgU++S5N3MQjDPpDvP9yUTDXKhkTs5xkyokm0C/zORmZyjM//mMUzKaxo OB1/L/TmKx8gCpj5jkCRESSSwuXJF9w+xMz0Woh7u41Cp3BFmAeTu+OtIjYdkijo15 W0iMyL5iC7g1Q== From: Sasha Levin To: lance.yang@linux.dev, samarth.colleges@gmail.com, akpm@linux-foundation.org, ljs@kernel.org, kas@kernel.org, david@kernel.org, mgorman@techsingularity.net, xu.xin@linux.dev, chengming.zhou@linux.dev, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jglisse@redhat.com, aarcange@redhat.com, peterx@redhat.com, bobbypowers@gmail.com, bgeffon@google.com, dplotnikov@virtuozzo.com, dgilbert@interlog.com, hughd@google.com, hannes@cmpxchg.org, cracauer@cons.org, mcfadden8@llnl.gov, gokhale2@llnl.gov, xemul@openvz.org, riel@surriel.com, shli@fb.com, jthoughton@google.com, corbet@lwn.net, pbonzini@redhat.com, seanjc@google.com, sj@kernel.org, ziy@nvidia.com, med08elkadiri@gmail.com Cc: stable@vger.kernel.org Subject: FAILED: patch "[PATCH] mm/ksm: fix userfaultfd protection during merge and unmerge" failed to apply to 6.6-stable tree Date: Mon, 9 Nov 2026 20:12:22 -0500 Message-ID: <20261109201222-failed-6.6-990d6c2194a9@kernel.org> X-Mailer: git-send-email 2.53.0 X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 990d6c2194a938a19a8cf94c6cfd75171345089b # git commit -s git send-email --to '' --in-reply-to '20261109201222-failed-6.6-990d6c2194a9@kernel.org' --subject-prefix 'PATCH 6.6.y' 'HEAD^..' Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From 990d6c2194a938a19a8cf94c6cfd75171345089b Mon Sep 17 00:00:00 2001 From: Lance Yang Date: Mon, 26 Oct 2026 21:00:54 +0800 Subject: [PATCH] mm/ksm: fix userfaultfd protection during merge and unmerge MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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(-) diff --git a/mm/ksm.c b/mm/ksm.c index 910a1307ac9f3..d6f736a1aa2f9 100644 --- a/mm/ksm.c +++ b/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_struct *vma, struct page *page, 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))); /* diff --git a/mm/memory.c b/mm/memory.c index 916637e8381da..b65b56fe97148 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4125,8 +4125,11 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf) 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(struct vm_fault *vmf) * 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); -- 2.53.0