From: Kiryl Shutsemau <kas@kernel.org>
To: akpm@linux-foundation.org, rppt@kernel.org, peterx@redhat.com,
david@kernel.org
Cc: ljs@kernel.org, surenb@google.com, vbabka@kernel.org,
Liam.Howlett@oracle.com, ziy@nvidia.com, corbet@lwn.net,
skhan@linuxfoundation.org, seanjc@google.com,
pbonzini@redhat.com, jthoughton@google.com, aarcange@redhat.com,
sj@kernel.org, usama.arif@linux.dev, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kselftest@vger.kernel.org, kvm@vger.kernel.org,
kernel-team@meta.com
Subject: Re: [PATCH 09/14] mm/userfaultfd: add RWP fault delivery and expose UFFDIO_REGISTER_MODE_RWP
Date: Thu, 30 Apr 2026 17:51:24 +0100 [thread overview]
Message-ID: <afOH-MzZVT8Kuk-6@thinkstation> (raw)
In-Reply-To: <20260427114607.4068647-10-kas@kernel.org>
sashiko.dev -- https://sashiko.dev/#/patchset/20260427114607.4068647-1-kas@kernel.org -- wrote:
> Does this code lose the RWP read protection after a page is swapped out
> and back in?
> [ ... ]
> The restored PTE will be PROT_READ with the uffd bit set, instead of
> PROT_NONE. Will this silently allow subsequent read accesses to succeed
> without triggering the required RWP userfault?
The PROT_NONE restoration on swap-in is performed two commits earlier,
in patch 6/14 "mm: preserve RWP marker across PTE rewrites", which
adds to do_swap_page():
if (pte_swp_uffd(vmf->orig_pte) && userfaultfd_rwp(vma))
pte = pte_modify(pte, PAGE_NONE);
so a swapped-in RWP page comes back as PAGE_NONE | _PAGE_UFFD, not
PROT_READ | _PAGE_UFFD. The same patch covers unuse_pte() (the
swapoff(2) path), restore_exclusive_pte(), and the migration-entry
resolvers; each gates on userfaultfd_rwp(vma) and the swap-pte uffd
bit before re-applying PAGE_NONE.
> Can this sequence cause a state collision between RWP and NUMA-hinted
> UFFD_WP pages?
> If a VMA has both VM_UFFD_WP and VM_UFFD_RWP enabled, [ ... ]
No. VM_UFFD_WP and VM_UFFD_RWP are mutually exclusive.
--
Kiryl Shutsemau / Kirill A. Shutemov
next prev parent reply other threads:[~2026-04-30 16:51 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-27 11:45 [PATCH 00/14] userfaultfd: working set tracking for VM guest memory Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 01/14] mm: decouple protnone helpers from CONFIG_NUMA_BALANCING Kiryl Shutsemau (Meta)
2026-04-30 4:47 ` SeongJae Park
2026-04-27 11:45 ` [PATCH 02/14] mm: rename uffd-wp PTE bit macros to uffd Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 03/14] mm: rename uffd-wp PTE accessors " Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 04/14] mm: add VM_UFFD_RWP VMA flag Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 05/14] mm: add MM_CP_UFFD_RWP change_protection() flag Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 06/14] mm: preserve RWP marker across PTE rewrites Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 07/14] mm: handle VM_UFFD_RWP in khugepaged, rmap, and GUP Kiryl Shutsemau (Meta)
2026-04-30 16:28 ` Kiryl Shutsemau
2026-04-30 16:31 ` Kiryl Shutsemau
2026-04-27 11:45 ` [PATCH 08/14] userfaultfd: add UFFDIO_REGISTER_MODE_RWP and UFFDIO_RWPROTECT plumbing Kiryl Shutsemau (Meta)
2026-04-30 16:46 ` Kiryl Shutsemau
2026-04-27 11:45 ` [PATCH 09/14] mm/userfaultfd: add RWP fault delivery and expose UFFDIO_REGISTER_MODE_RWP Kiryl Shutsemau (Meta)
2026-04-30 16:51 ` Kiryl Shutsemau [this message]
2026-04-27 11:45 ` [PATCH 10/14] mm/pagemap: add PAGE_IS_ACCESSED for RWP tracking Kiryl Shutsemau (Meta)
2026-04-27 11:45 ` [PATCH 11/14] userfaultfd: add UFFD_FEATURE_RWP_ASYNC for async fault resolution Kiryl Shutsemau (Meta)
2026-04-27 11:46 ` [PATCH 12/14] userfaultfd: add UFFDIO_SET_MODE for runtime sync/async toggle Kiryl Shutsemau (Meta)
2026-04-27 11:46 ` [PATCH 13/14] selftests/mm: add userfaultfd RWP tests Kiryl Shutsemau (Meta)
2026-04-27 11:46 ` [PATCH 14/14] Documentation/userfaultfd: document RWP working set tracking Kiryl Shutsemau (Meta)
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