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Sun, 18 Oct 2026 08:21:27 +0000 X-Mizu-Trace-ID: 39d921597cd8dcbf X-Migadu-Flow: FLOW_OUT From: Lance Yang To: david@kernel.org Cc: akpm@linux-foundation.org, liam@infradead.org, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, pfalcato@suse.de, muchun.song@linux.dev, osalvador@suse.de, linmiaohe@huawei.com, nao.horiguchi@gmail.com, agl@us.ibm.com, mel@csn.ul.ie, riel@surriel.com, peterx@redhat.com, kas@kernel.org, rppt@kernel.org, josef@toxicpanda.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, mason@kernel.org Subject: Re: [PATCH 09/10] mm/hugetlb: don't leave a uffd-wp marker when zapping an RWP entry Date: Sun, 18 Oct 2026 16:21:13 +0800 Message-ID: <20261018082113.5548-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261015-urgent_fixes-v1-9-42796911043b@kernel.org> References: <20261015-urgent_fixes-v1-9-42796911043b@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 091A140005 X-Stat-Signature: yh7std1j8onqoj77r5uus7qksjqw86s8 X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1792311688-441885 X-HE-Meta: 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 iTiya5uK kPSlDSot6hUH+j9wtRwMXl/oOKeIFZzfpgFFoCX1VDjhDk/YRNGTD+VVotB4HWY72XPuQvVRbPnMcR6aEBSD158U2RQ7HHNzFK6hKETBnm+8tVHWC8Og+dLk9mB7SAiktNR6ALo5erIp6WTmWwd3X/cSbfHCEo76vsk5sGl71oymcIbg8URIV9TPDJsbIBiuu2gUkC5Fi2Z5La7zU39tyWGXHJq2yap9lQCbUo7kWasvuiUwuB5d9ciUp3RfGD0zWIuWW2fGDnG1Ub+RVuczTNSKfnNYe54vxhDWkxv07HqynWfpS4kj3hI54P1E078wAYJLBvdVMuzwm6zNJtawIdXZB+s6END8qSj7f8602zYfdaewVBUxHYf8CegsOppwHsetoyU/La9uj3Qk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Oct 15, 2026 at 06:07:15PM +0200, David Hildenbrand (Arm) wrote: >From: Josef Bacik > >An entry that is protected with UFFDIO_RWPROTECT is PAGE_NONE with the >uffd bit set, the bit that userfaultfd write protection uses too. When >__unmap_hugepage_range() zaps an entry with that bit it leaves a >PTE_MARKER_UFFD_WP behind, whatever the VMA is registered for. > >In a VMA registered with UFFDIO_REGISTER_MODE_RWP that marker means >nothing. The next fault has hugetlb_no_page() turn it into a present, >read-only entry with the uffd bit. That is not an RWP entry, since it is >not PAGE_NONE, and the VMA has no VM_UFFD_WP (the two modes can not be >registered together). An earlier fix solved some side effects, now just >stop the zap from wrongly installing a marker. > >Leave a marker only if the VMA is registered for write protection, both >for present and for non-present entries. The zap of ordinary page >tables has the same test, in cond_install_uffd_wp_ptes(), and >hugetlb_change_protection() says that "uffd_rwp does not install markers". > >After a zap the range of an RWP VMA is simply empty, as it is for >anonymous memory and shmem. Nothing changes for VMAs with VM_UFFD_WP. In >a VMA that is not registered at all a leftover uffd bit or marker is now >dropped by the zap and no longer kept alive. > >Original fix generated by an LLM and sent in private by Josef. > >Fixes: 2d427bb01639 ("mm/userfaultfd: add RWP fault delivery and expose UFFDIO_REGISTER_MODE_RWP") >Cc: stable@vger.kernel.org >Reported-by: Chris Mason >Signed-off-by: Josef Bacik >[ david: a bit of description overhaul+simplification ] >Signed-off-by: David Hildenbrand (Arm) >--- Reviewed-by: Lance Yang