[PATCH v11 2/5] mm: userfaultfd: Add pgtable_uffd_wp_supported()
David Hildenbrand
david at redhat.com
Fri Sep 12 01:54:19 PDT 2025
On 11.09.25 11:55, 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.
If you change the name of the sofdirty thingy, adjust that one here as well.
>
> Signed-off-by: Chunyan Zhang <zhangchunyan at iscas.ac.cn>
> ---
> fs/userfaultfd.c | 23 ++++++++--------
> include/asm-generic/pgtable_uffd.h | 11 ++++++++
> include/linux/mm_inline.h | 7 +++++
> include/linux/userfaultfd_k.h | 44 +++++++++++++++++++-----------
> mm/memory.c | 6 ++--
> 5 files changed, 62 insertions(+), 29 deletions(-)
>
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 54c6cc7fe9c6..b549c327d7ad 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_uffd_wp_supported())
> + goto out;
> +
> vm_flags |= VM_UFFD_WP;
I like that, similar to the softdirty thing we will simply not set the flag.
> }
> if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
> @@ -1980,14 +1980,15 @@ 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_uffd_wp_supported())
> + uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
> +
> + if (!IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP) ||
> + !pgtable_uffd_wp_supported()) {
I wonder if we would want to have a helper for that like
static inline bool uffd_supports_wp_marker(void)
{
return pgtable_uffd_wp_supported() && IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP);
}
That should clean all of this futher up.
> + 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..895d68ece0e7 100644
> --- a/include/asm-generic/pgtable_uffd.h
> +++ b/include/asm-generic/pgtable_uffd.h
> @@ -1,6 +1,17 @@
> #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 overiding it, please make sure the
s/overiding/overriding/
> + * CONFIG_HAVE_ARCH_USERFAULTFD_WP is part of this macro.
> + */
> +#ifndef pgtable_uffd_wp_supported
> +#define pgtable_uffd_wp_supported() IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_WP)
> +#endif
> #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 89b518ff097e..38845b8b79ff 100644
> --- a/include/linux/mm_inline.h
> +++ b/include/linux/mm_inline.h
> @@ -571,6 +571,13 @@ 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
> + /*
> + * Some platforms can customize the PTE uffd-wp bit, making it unavailable
> + * even if the architecture allows providing the PTE resource.
> + */
> + if (!pgtable_uffd_wp_supported())
> + return false;
> +
Likely we could use the uffd_supports_wp_marker() wrapper here isntead and
remove the #ifdef.
> bool arm_uffd_pte = false;
>
> /* The current status of the pte should be "cleared" before calling */
> diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
> index c0e716aec26a..6264b56ae961 100644
> --- a/include/linux/userfaultfd_k.h
> +++ b/include/linux/userfaultfd_k.h
> @@ -228,15 +228,15 @@ 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 ((!IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP) ||
> + !pgtable_uffd_wp_supported()) &&
This would also use the helper.
> + (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) ||
> @@ -437,8 +437,11 @@ static inline bool userfaultfd_wp_use_markers(struct vm_area_struct *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);
> + if (pgtable_uffd_wp_supported())
> + return is_pte_marker_entry(entry) &&
> + (pte_marker_get(entry) & PTE_MARKER_UFFD_WP);
> + else
> + return false;
if (!uffd_supports_wp_marker())
return false;
return is_pte_marker_entry(entry) &&
(pte_marker_get(entry) & PTE_MARKER_UFFD_WP);
> #else
> return false;
> #endif
> @@ -447,14 +450,19 @@ static inline bool pte_marker_entry_uffd_wp(swp_entry_t entry)
> static inline bool pte_marker_uffd_wp(pte_t pte)
> {
> #ifdef CONFIG_PTE_MARKER_UFFD_WP
Simialrly here, just do a
if (!uffd_supports_wp_marker())
return false;
and remove the ifdef
> #endif
> @@ -467,14 +475,18 @@ static inline bool pte_marker_uffd_wp(pte_t pte)
> static inline bool pte_swp_uffd_wp_any(pte_t pte)
> {
> #ifdef CONFIG_PTE_MARKER_UFFD_WP
Same here.
> - if (!is_swap_pte(pte))
> - return false;
> + if (pgtable_uffd_wp_supported()) {
> + if (!is_swap_pte(pte))
> + return false;
>
> - if (pte_swp_uffd_wp(pte))
> - return true;
> + if (pte_swp_uffd_wp(pte))
> + return true;
>
> - if (pte_marker_uffd_wp(pte))
> - return true;
> + if (pte_marker_uffd_wp(pte))
> + return true;
> + } else {
> + return false;
> + }
> #endif
> return false;
> }
> diff --git a/mm/memory.c b/mm/memory.c
> index 0ba4f6b71847..4eb05c5f487b 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1465,7 +1465,9 @@ zap_install_uffd_wp_if_needed(struct vm_area_struct *vma,
> {
> bool was_installed = false;
>
> -#ifdef CONFIG_PTE_MARKER_UFFD_WP
> + if (!IS_ENABLED(CONFIG_PTE_MARKER_UFFD_WP) || !pgtable_uffd_wp_supported())
> + return false;
> +
Same here.
--
Cheers
David / dhildenb
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