From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Jonathan Corbet <corbet@lwn.net>,
Shuah Khan <skhan@linuxfoundation.org>,
Randy Dunlap <rdunlap@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Liam R. Howlett" <liam@infradead.org>,
Lorenzo Stoakes <ljs@kernel.org>,
Vlastimil Babka <vbabka@kernel.org>, Jann Horn <jannh@google.com>,
Pedro Falcato <pfalcato@suse.de>, Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, Peter Xu <peterx@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Zi Yan <ziy@nvidia.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Nico Pache <nico.pache@linux.dev>,
Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>,
Barry Song <baohua@kernel.org>, Lance Yang <lance.yang@linux.dev>,
Usama Arif <usama.arif@linux.dev>,
Kiryl Shutsemau <kas@kernel.org>,
Axel Rasmussen <axelrasmussen@google.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-doc@vger.kernel.org, linux-mm@kvack.org,
linux-trace-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] mm/userfaultfd: prevent poison marker loss
Date: Sat, 14 Nov 2026 16:39:44 +0100 [thread overview]
Message-ID: <822c1c7e-bfdf-4570-bf30-08f187e7253d@kernel.org> (raw)
In-Reply-To: <20261107-b4-uffd_marker_loss-v1-1-82926b22704c@kernel.org>
On 11/7/26 00:51, David Hildenbrand (Arm) wrote:
> Unregistering userfaultfd leaves poison markers in the page tables.
> However, once unregistered, hugetlb PMD tables can be shared again.
>
> Further, shmem page-table retraction can discard poison markers even
> while registered in missing mode, and fork() can skip copying page
> tables containing poison markers.
>
> To fix it, add VM_MAYBE_UFFD_POISON and set it before installing poison
> markers. Preserve it across unregistration, splits, merges and fork(),
> just like we do with guard markers.
>
> Use the new atomic VMA flag to disable PMD sharing and page-table
> retraction, and to force page-table copying during fork().
>
> Move VM_UFFD_WP to bit 44 and make HAVE_ARCH_USERFAULTFD_WP depend on
> 64BIT, freeing bit 12 for the new flag on both 32-bit and 64-bit systems.
> Expose the flag as "up" in smaps.
>
> Losing poison markers, while unpleasant, is not really fatal, and the
> use case is rather a niche thing. In addition, we rely on the atomic
> VMA flags infrastructure ... so let's not CC stable.
>
> Fixes: fc71884a5f59 ("mm: userfaultfd: add new UFFDIO_POISON ioctl")
> Fixes: 8a13897fb0da ("mm: userfaultfd: support UFFDIO_POISON for hugetlbfs")
> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
> ---
Ping on this one.
--
Cheers,
David
next prev parent reply other threads:[~2026-11-14 15:39 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-06 23:51 [PATCH 0/2] mm/userfaultfd: prevent poison marker loss David Hildenbrand (Arm)
2026-11-06 23:51 ` [PATCH 1/2] " David Hildenbrand (Arm)
2026-11-14 15:39 ` David Hildenbrand (Arm) [this message]
2026-11-06 23:51 ` [PATCH 2/2] mm/khugepaged: check for empty PTE tables before retracting David Hildenbrand (Arm)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=822c1c7e-bfdf-4570-bf30-08f187e7253d@kernel.org \
--to=david@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=axelrasmussen@google.com \
--cc=baohua@kernel.org \
--cc=baolin.wang@linux.alibaba.com \
--cc=corbet@lwn.net \
--cc=dev.jain@arm.com \
--cc=jannh@google.com \
--cc=kas@kernel.org \
--cc=lance.yang@linux.dev \
--cc=liam@infradead.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-trace-kernel@vger.kernel.org \
--cc=ljs@kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mhiramat@kernel.org \
--cc=mhocko@suse.com \
--cc=nico.pache@linux.dev \
--cc=peterx@redhat.com \
--cc=pfalcato@suse.de \
--cc=rdunlap@infradead.org \
--cc=rostedt@goodmis.org \
--cc=rppt@kernel.org \
--cc=ryan.roberts@arm.com \
--cc=skhan@linuxfoundation.org \
--cc=surenb@google.com \
--cc=usama.arif@linux.dev \
--cc=vbabka@kernel.org \
--cc=ziy@nvidia.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox