From: "Jose A. Perez de Azpillaga" <azpijr@gmail.com>
To: Tal Zussman <tz2294@columbia.edu>, Kiryl Shutsemau <kas@kernel.org>
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>,
"Matthew Brost" <matthew.brost@intel.com>,
"Joshua Hahn" <joshua.hahnjy@gmail.com>,
"Byungchul Park" <byungchul@sk.com>,
"Gregory Price" <gourry@gourry.net>,
"Ying Huang" <ying.huang@linux.alibaba.com>,
"Alistair Popple" <apopple@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>,
"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: Thu, 12 Nov 2026 10:40:38 +0100 [thread overview]
Message-ID: <db9ed03f-0b85-4360-a2e9-f6719773c7eb@gmail.com> (raw)
In-Reply-To: <e19f1fff-f1a7-4c2b-8908-2d3ee6a49069@columbia.edu>
On 11/12/26 12:21 AM, Tal Zussman wrote:
> + Jose
>
> On 11/11/26 2:25 PM, Kiryl Shutsemau wrote:
>> 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.
>>
> So this makes sense, but I think this gets at the documentation point
> raised in the other thread. It seems that to use sync RWP "properly" it
> needs to be combined with MINOR for shmem and hugetlb (and MISSING for
> holes) and with MISSING for anonymous memory. Is that accurate? If so,
> this should be stated much more explicitly in the documentation + man
> page. I see that co-registering with MISSING is mentioned, but not the
> rest of the points (reclaim, collapse, etc.) The example in
> userfaultfd.rst also registers a MAP_SHARED mapping only with RWP and
> MISSING, no MINOR, so that should be clarified too. Hopefully this will
> make it into Jose's documentation patch.
okay, if Kiryl is okay with that I will add it to my upcoming patch.
--
cheers,
jose a. p-a
next prev parent reply other threads:[~2026-11-12 9:40 UTC|newest]
Thread overview: 19+ 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 22:39 ` Tal Zussman
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
2026-11-11 23:21 ` Tal Zussman
2026-11-12 9:40 ` Jose A. Perez de Azpillaga [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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