From: Kiryl Shutsemau <kas@kernel.org>
To: Tal Zussman <tz2294@columbia.edu>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Mike Rapoport" <rppt@kernel.org>, "Peter Xu" <peterx@redhat.com>,
"James Houghton" <jthoughton@google.com>,
"Andrea Arcangeli" <aarcange@redhat.com>,
"Suren Baghdasaryan" <surenb@google.com>,
"Balbir Singh" <balbirs@nvidia.com>,
"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>,
"Michał Mirosław" <mirq-linux@rere.qmqm.pl>,
"Andrei Vagin" <avagin@gmail.com>,
"Stephen Rothwell" <sfr@canb.auug.org.au>,
"Arnd Bergmann" <arnd@arndb.de>,
"Muhammad Usama Anjum" <usama.anjum@arm.com>,
"David Hildenbrand" <david@kernel.org>, "Zi Yan" <ziy@nvidia.com>,
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"Ying Huang" <ying.huang@linux.alibaba.com>,
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"Dev Jain" <dev.jain@arm.com>, "Barry Song" <baohua@kernel.org>,
"Lance Yang" <lance.yang@linux.dev>,
"Usama Arif" <usama.arif@linux.dev>,
"Chris Down" <chris@chrisdown.name>,
"Muchun Song" <muchun.song@linux.dev>,
"Oscar Salvador" <osalvador@suse.de>,
"Mikołaj Lenczewski" <miko.lenczewski@arm.com>,
"Michal Hocko" <mhocko@suse.com>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 11/12] mm/madvise: send UFFD_EVENT_REMOVE when installing guard regions
Date: Wed, 11 Nov 2026 19:25:27 +0000 [thread overview]
Message-ID: <avTA58zlxJZ69TB8@thinkstation> (raw)
In-Reply-To: <20261111-uffd-state-fixes-v1-11-00713d368976@columbia.edu>
On Wed, Nov 11, 2026 at 12:55:19PM -0500, Tal Zussman wrote:
> On an anonymous VMA, the zap drops uffd-wp and RWP protection along with
> the pages. Writes and accesses to the range after the guard is removed
> are then not reported, and the manager cannot know that it has to
> protect the range again.
For RWP this only holds if the range is registered without MISSING.
The zap frees the pages, so with MISSING the first access after the
guard is removed is reported as a missing fault. And there is nothing to
protect again: RWP only covers present PTEs, and a page faulted back in
shows up as accessed in PAGEMAP_SCAN.
--
Kiryl Shutsemau / Kirill A. Shutemov
next prev parent reply other threads:[~2026-11-11 19:25 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-11 17:55 [PATCH 00/12] userfaultfd: assorted fixes (part 1) Tal Zussman
2026-11-11 17:55 ` [PATCH 01/12] userfaultfd: use anonymous memory for UFFDIO_ZEROPAGE on private file mappings Tal Zussman
2026-11-11 17:55 ` [PATCH 02/12] userfaultfd: refuse UFFDIO_MOVE into a non-present huge destination PMD Tal Zussman
2026-11-11 17:55 ` [PATCH 03/12] fs/proc/task_mmu: downgrade writable migration entries in PAGEMAP_SCAN write-protect Tal Zussman
2026-11-11 17:55 ` [PATCH 04/12] mm/migrate: keep the uffd bit when restoring a writable migration entry Tal Zussman
2026-11-11 17:55 ` [PATCH 05/12] fs/proc/task_mmu: write-protect device-private THPs in PAGEMAP_SCAN Tal Zussman
2026-11-11 17:55 ` [PATCH 06/12] mm/huge_memory: build the moved huge zero PMD from the destination VMA Tal Zussman
2026-11-11 19:12 ` Kiryl Shutsemau
2026-11-11 17:55 ` [PATCH 07/12] mm/mremap: resolve uffd state when the context is dropped, not during the move Tal Zussman
2026-11-11 19:20 ` Kiryl Shutsemau
2026-11-11 17:55 ` [PATCH 08/12] mm/migrate_device: do not migrate a uffd-protected zero page Tal Zussman
2026-11-11 17:55 ` [PATCH 09/12] mm/madvise: let a guard marker carry the uffd-wp bit Tal Zussman
2026-11-11 17:55 ` [PATCH 10/12] mm: set the uffd-wp bit on a guard marker when write-protecting Tal Zussman
2026-11-11 17:55 ` [PATCH 11/12] mm/madvise: send UFFD_EVENT_REMOVE when installing guard regions Tal Zussman
2026-11-11 19:25 ` Kiryl Shutsemau [this message]
2026-11-11 17:55 ` [PATCH 12/12] mm/userfaultfd: check hugetlb end alignment in UFFDIO_UNREGISTER pre-scan Tal Zussman
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