Some platforms can customize the PTE/PMD entry uffd-wp bit making
it unavailable even if the architecture provides the resource.
This patch adds a macro API that allows architectures to define their
specific implementations to check if the uffd-wp bit is available
on which device the kernel is running.
Also this patch is removing "ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP" and
"ifdef CONFIG_PTE_MARKER_UFFD_WP" in favor of pgtable_supports_uffd_wp()
and uffd_supports_wp_marker() checks respectively that default to
IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) and
"IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) && IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP)"
if not overridden by the architecture, no change in behavior is expected.
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
---
fs/userfaultfd.c | 22 +++---
include/asm-generic/pgtable_uffd.h | 17 +++++
include/linux/mm_inline.h | 12 ++-
include/linux/userfaultfd_k.h | 114 ++++++++++++++++-------------
mm/memory.c | 6 +-
5 files changed, 106 insertions(+), 65 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 54c6cc7fe9c6..e41736ffa202 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1270,9 +1270,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
vm_flags |= VM_UFFD_MISSING;
if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
-#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
- goto out;
-#endif
+ if (!pgtable_supports_uffd_wp())
+ goto out;
+
vm_flags |= VM_UFFD_WP;
}
if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
@@ -1980,14 +1980,14 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
uffdio_api.features &=
~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
#endif
-#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
- uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
-#endif
-#ifndef CONFIG_PTE_MARKER_UFFD_WP
- uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
- uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
- uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC;
-#endif
+ if (!pgtable_supports_uffd_wp())
+ uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
+
+ if (!uffd_supports_wp_marker()) {
+ uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
+ uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
+ uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC;
+ }
ret = -EINVAL;
if (features & ~uffdio_api.features)
diff --git a/include/asm-generic/pgtable_uffd.h b/include/asm-generic/pgtable_uffd.h
index 828966d4c281..0d85791efdf7 100644
--- a/include/asm-generic/pgtable_uffd.h
+++ b/include/asm-generic/pgtable_uffd.h
@@ -1,6 +1,23 @@
#ifndef _ASM_GENERIC_PGTABLE_UFFD_H
#define _ASM_GENERIC_PGTABLE_UFFD_H
+/*
+ * Some platforms can customize the uffd-wp bit, making it unavailable
+ * even if the architecture provides the resource.
+ * Adding this API allows architectures to add their own checks for the
+ * devices on which the kernel is running.
+ * Note: When overriding it, please make sure the
+ * CONFIG_HAVE_ARCH_USERFAULTFD_WP is part of this macro.
+ */
+#ifndef pgtable_supports_uffd_wp
+#define pgtable_supports_uffd_wp() IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP)
+#endif
+
+static inline bool uffd_supports_wp_marker(void)
+{
+ return pgtable_supports_uffd_wp() && IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP);
+}
+
#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
static __always_inline int pte_uffd_wp(pte_t pte)
{
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index d6c1011b38f2..c69162812ba6 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -553,7 +553,6 @@ static inline pte_marker copy_pte_marker(
return dstm;
}
-#endif
/*
* If this pte is wr-protected by uffd-wp in any form, arm the special pte to
@@ -571,9 +570,15 @@ static inline bool
pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr,
pte_t *pte, pte_t pteval)
{
-#ifdef CONFIG_PTE_MARKER_UFFD_WP
bool arm_uffd_pte = false;
+ /*
+ * Some platforms can customize the PTE uffd-wp bit, making it unavailable
+ * even if the architecture allows providing the PTE resource.
+ */
+ if (!uffd_supports_wp_marker())
+ return false;
+
/* The current status of the pte should be "cleared" before calling */
WARN_ON_ONCE(!pte_none(ptep_get(pte)));
@@ -602,7 +607,7 @@ pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr,
make_pte_marker(PTE_MARKER_UFFD_WP));
return true;
}
-#endif
+
return false;
}
@@ -616,5 +621,6 @@ static inline bool vma_has_recency(const struct vm_area_struct *vma)
return true;
}
+#endif
#endif
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index c0e716aec26a..4ccc79b5731e 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -228,15 +228,14 @@ static inline bool vma_can_userfault(struct vm_area_struct *vma,
if (wp_async && (vm_flags == VM_UFFD_WP))
return true;
-#ifndef CONFIG_PTE_MARKER_UFFD_WP
/*
* If user requested uffd-wp but not enabled pte markers for
* uffd-wp, then shmem & hugetlbfs are not supported but only
* anonymous.
*/
- if ((vm_flags & VM_UFFD_WP) && !vma_is_anonymous(vma))
+ if (!uffd_supports_wp_marker() && (vm_flags & VM_UFFD_WP) &&
+ !vma_is_anonymous(vma))
return false;
-#endif
/* By default, allow any of anon|shmem|hugetlb */
return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
@@ -291,6 +290,67 @@ void userfaultfd_release_new(struct userfaultfd_ctx *ctx);
void userfaultfd_release_all(struct mm_struct *mm,
struct userfaultfd_ctx *ctx);
+static inline bool userfaultfd_wp_use_markers(struct vm_area_struct *vma)
+{
+ /* Only wr-protect mode uses pte markers */
+ if (!userfaultfd_wp(vma))
+ return false;
+
+ /* File-based uffd-wp always need markers */
+ if (!vma_is_anonymous(vma))
+ return true;
+
+ /*
+ * Anonymous uffd-wp only needs the markers if WP_UNPOPULATED
+ * enabled (to apply markers on zero pages).
+ */
+ return userfaultfd_wp_unpopulated(vma);
+}
+
+static inline bool pte_marker_entry_uffd_wp(swp_entry_t entry)
+{
+ if (!uffd_supports_wp_marker())
+ return false;
+
+ return is_pte_marker_entry(entry) &&
+ (pte_marker_get(entry) & PTE_MARKER_UFFD_WP);
+}
+
+static inline bool pte_marker_uffd_wp(pte_t pte)
+{
+ swp_entry_t entry;
+
+ if (!uffd_supports_wp_marker())
+ return false;
+
+ if (!is_swap_pte(pte))
+ return false;
+
+ entry = pte_to_swp_entry(pte);
+
+ return pte_marker_entry_uffd_wp(entry);
+}
+
+/*
+ * Returns true if this is a swap pte and was uffd-wp wr-protected in either
+ * forms (pte marker or a normal swap pte), false otherwise.
+ */
+static inline bool pte_swp_uffd_wp_any(pte_t pte)
+{
+ if (!uffd_supports_wp_marker())
+ return false;
+
+ if (!is_swap_pte(pte))
+ return false;
+
+ if (pte_swp_uffd_wp(pte))
+ return true;
+
+ if (pte_marker_uffd_wp(pte))
+ return true;
+
+ return false;
+}
#else /* CONFIG_USERFAULTFD */
/* mm helpers */
@@ -415,68 +475,24 @@ static inline bool vma_has_uffd_without_event_remap(struct vm_area_struct *vma)
return false;
}
-#endif /* CONFIG_USERFAULTFD */
-
static inline bool userfaultfd_wp_use_markers(struct vm_area_struct *vma)
{
- /* Only wr-protect mode uses pte markers */
- if (!userfaultfd_wp(vma))
return false;
-
- /* File-based uffd-wp always need markers */
- if (!vma_is_anonymous(vma))
- return true;
-
- /*
- * Anonymous uffd-wp only needs the markers if WP_UNPOPULATED
- * enabled (to apply markers on zero pages).
- */
- return userfaultfd_wp_unpopulated(vma);
}
static inline bool pte_marker_entry_uffd_wp(swp_entry_t entry)
{
-#ifdef CONFIG_PTE_MARKER_UFFD_WP
- return is_pte_marker_entry(entry) &&
- (pte_marker_get(entry) & PTE_MARKER_UFFD_WP);
-#else
- return false;
-#endif
+ return false;
}
static inline bool pte_marker_uffd_wp(pte_t pte)
{
-#ifdef CONFIG_PTE_MARKER_UFFD_WP
- swp_entry_t entry;
-
- if (!is_swap_pte(pte))
return false;
-
- entry = pte_to_swp_entry(pte);
-
- return pte_marker_entry_uffd_wp(entry);
-#else
- return false;
-#endif
}
-/*
- * Returns true if this is a swap pte and was uffd-wp wr-protected in either
- * forms (pte marker or a normal swap pte), false otherwise.
- */
static inline bool pte_swp_uffd_wp_any(pte_t pte)
{
-#ifdef CONFIG_PTE_MARKER_UFFD_WP
- if (!is_swap_pte(pte))
return false;
-
- if (pte_swp_uffd_wp(pte))
- return true;
-
- if (pte_marker_uffd_wp(pte))
- return true;
-#endif
- return false;
}
-
+#endif /* CONFIG_USERFAULTFD */
#endif /* _LINUX_USERFAULTFD_K_H */
diff --git a/mm/memory.c b/mm/memory.c
index 39ed698dfc37..a47621b35194 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1593,7 +1593,9 @@ zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
{
bool was_installed = false;
-#ifdef CONFIG_PTE_MARKER_UFFD_WP
+ if (!uffd_supports_wp_marker())
+ return false;
+
/* Zap on anonymous always means dropping everything */
if (vma_is_anonymous(vma))
return false;
@@ -1610,7 +1612,7 @@ zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
pte++;
addr += PAGE_SIZE;
}
-#endif
+
return was_installed;
}
--
2.34.1On 17.09.25 05:36, Chunyan Zhang wrote:
> Some platforms can customize the PTE/PMD entry uffd-wp bit making
> it unavailable even if the architecture provides the resource.
> This patch adds a macro API that allows architectures to define their
> specific implementations to check if the uffd-wp bit is available
> on which device the kernel is running.
>
> Also this patch is removing "ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP" and
> "ifdef CONFIG_PTE_MARKER_UFFD_WP" in favor of pgtable_supports_uffd_wp()
> and uffd_supports_wp_marker() checks respectively that default to
> IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) and
> "IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) && IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP)"
> if not overridden by the architecture, no change in behavior is expected.
>
> Acked-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
> ---
[...]
Taking another look.
> /* mm helpers */
> @@ -415,68 +475,24 @@ static inline bool vma_has_uffd_without_event_remap(struct vm_area_struct *vma)
> return false;
> }
>
> -#endif /* CONFIG_USERFAULTFD */
> -
> static inline bool userfaultfd_wp_use_markers(struct vm_area_struct *vma)
> {
> - /* Only wr-protect mode uses pte markers */
> - if (!userfaultfd_wp(vma))
> return false;
Isn't this indented one level too deep?
> -
> - /* File-based uffd-wp always need markers */
> - if (!vma_is_anonymous(vma))
> - return true;
> -
> - /*
> - * Anonymous uffd-wp only needs the markers if WP_UNPOPULATED
> - * enabled (to apply markers on zero pages).
> - */
> - return userfaultfd_wp_unpopulated(vma);
> }
>
> static inline bool pte_marker_entry_uffd_wp(swp_entry_t entry)
> {
> -#ifdef CONFIG_PTE_MARKER_UFFD_WP
> - return is_pte_marker_entry(entry) &&
> - (pte_marker_get(entry) & PTE_MARKER_UFFD_WP);
> -#else
> - return false;
> -#endif
> + return false;
Same here.
> }
>
> static inline bool pte_marker_uffd_wp(pte_t pte)
> {
> -#ifdef CONFIG_PTE_MARKER_UFFD_WP
> - swp_entry_t entry;
> -
> - if (!is_swap_pte(pte))
> return false;
Same here.
> -
> - entry = pte_to_swp_entry(pte);
> -
> - return pte_marker_entry_uffd_wp(entry);
> -#else
> - return false;
> -#endif
> }
--
Cheers
David / dhildenb
On Wed, 17 Sept 2025 at 15:25, David Hildenbrand <david@redhat.com> wrote:
>
> On 17.09.25 05:36, Chunyan Zhang wrote:
> > Some platforms can customize the PTE/PMD entry uffd-wp bit making
> > it unavailable even if the architecture provides the resource.
> > This patch adds a macro API that allows architectures to define their
> > specific implementations to check if the uffd-wp bit is available
> > on which device the kernel is running.
> >
> > Also this patch is removing "ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP" and
> > "ifdef CONFIG_PTE_MARKER_UFFD_WP" in favor of pgtable_supports_uffd_wp()
> > and uffd_supports_wp_marker() checks respectively that default to
> > IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) and
> > "IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP) && IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP)"
> > if not overridden by the architecture, no change in behavior is expected.
> >
> > Acked-by: David Hildenbrand <david@redhat.com>
> > Signed-off-by: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
> > ---
>
> [...]
>
> Taking another look.
>
> > /* mm helpers */
> > @@ -415,68 +475,24 @@ static inline bool vma_has_uffd_without_event_remap(struct vm_area_struct *vma)
> > return false;
> > }
> >
> > -#endif /* CONFIG_USERFAULTFD */
> > -
> > static inline bool userfaultfd_wp_use_markers(struct vm_area_struct *vma)
> > {
> > - /* Only wr-protect mode uses pte markers */
> > - if (!userfaultfd_wp(vma))
> > return false;
>
> Isn't this indented one level too deep?
Oh right, I will fix these.
Thanks to you spotting them out!
Chunyan
>
> > -
> > - /* File-based uffd-wp always need markers */
> > - if (!vma_is_anonymous(vma))
> > - return true;
> > -
> > - /*
> > - * Anonymous uffd-wp only needs the markers if WP_UNPOPULATED
> > - * enabled (to apply markers on zero pages).
> > - */
> > - return userfaultfd_wp_unpopulated(vma);
> > }
> >
> > static inline bool pte_marker_entry_uffd_wp(swp_entry_t entry)
> > {
> > -#ifdef CONFIG_PTE_MARKER_UFFD_WP
> > - return is_pte_marker_entry(entry) &&
> > - (pte_marker_get(entry) & PTE_MARKER_UFFD_WP);
> > -#else
> > - return false;
> > -#endif
> > + return false;
>
> Same here.
>
> > }
> >
> > static inline bool pte_marker_uffd_wp(pte_t pte)
> > {
> > -#ifdef CONFIG_PTE_MARKER_UFFD_WP
> > - swp_entry_t entry;
> > -
> > - if (!is_swap_pte(pte))
> > return false;
>
> Same here.
>
> > -
> > - entry = pte_to_swp_entry(pte);
> > -
> > - return pte_marker_entry_uffd_wp(entry);
> > -#else
> > - return false;
> > -#endif
> > }
>
>
> --
> Cheers
>
> David / dhildenb
>
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