[merged mm-stable] mm-fold-userfaultfd_rwp-to-false-without-config_arch_has_pte_protnone.patch removed from -mm tree

[merged mm-stable] mm-fold-userfaultfd_rwp-to-false-without-config_arch_has_pte_protnone.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm: fold userfaultfd_rwp() to false without CONFIG_ARCH_HAS_PTE_PROTNONE
has been removed from the -mm tree.  Its filename was
     mm-fold-userfaultfd_rwp-to-false-without-config_arch_has_pte_protnone.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>
Subject: mm: fold userfaultfd_rwp() to false without CONFIG_ARCH_HAS_PTE_PROTNONE
Date: Mon, 27 Jul 2026 10:16:11 +0100

RWP tracks accesses by installing PAGE_NONE (protnone) PTEs, so its code
paths are gated on userfaultfd_rwp().  Without
CONFIG_ARCH_HAS_PTE_PROTNONE there is no PAGE_NONE -- <linux/pgtable.h>
defines it to a BUILD_BUG() stub, relying on callers folding such paths to
dead code via IS_ENABLED(CONFIG_ARCH_HAS_PTE_PROTNONE).

userfaultfd_rwp() was not a compile-time constant, so the compiler could
not fold those paths.  With an older compiler (gcc 8.5.0, sparc64) the
PAGE_NONE reference in move_pages_huge_pmd() survived to codegen:

  mm/huge_memory.c:2874: _dst_pmd = pmd_modify(_dst_pmd, PAGE_NONE);
  compiler_types.h:702: error: call to '__compiletime_assert_501'
    declared with attribute error: BUILD_BUG failed

RWP cannot exist without protnone, so return a compile-time false when
CONFIG_ARCH_HAS_PTE_PROTNONE is unset; every RWP path then folds away.

Link: https://lore.kernel.org/amcitKvUvFYr8W38@thinkstation
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202607250853.VaJWGLeA-lkp@intel.com/
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: James Houghton <jthoughton@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/userfaultfd_k.h |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/include/linux/userfaultfd_k.h~mm-fold-userfaultfd_rwp-to-false-without-config_arch_has_pte_protnone
+++ a/include/linux/userfaultfd_k.h
@@ -221,6 +221,12 @@ static inline bool userfaultfd_minor(str
 
 static inline bool userfaultfd_rwp(struct vm_area_struct *vma)
 {
+	/*
+	 * Callers gate PAGE_NONE usage on this; PAGE_NONE is a BUILD_BUG()
+	 * without CONFIG_ARCH_HAS_PTE_PROTNONE, so fold to false.
+	 */
+	if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_PROTNONE))
+		return false;
 	return vma_test_single_mask(vma, VMA_UFFD_RWP);
 }
 
_

Patches currently in -mm which might be from kas@kernel.org are