mm: userfaultfd: add pgtable_supports_uffd_wp()

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 pgtable_supports_uffd_wp() 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.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Chunyan Zhang <[e-mail]>
Acked-by: David Hildenbrand <[e-mail]>
Cc: Albert Ou <[e-mail]>
Cc: Alexandre Ghiti <[e-mail]>
Cc: Alexandre Ghiti <[e-mail]>
Cc: Al Viro <[e-mail]>
Cc: Andrew Jones <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Axel Rasmussen <[e-mail]>
Cc: Christian Brauner <[e-mail]>
Cc: Conor Dooley <[e-mail]>
Cc: Conor Dooley <[e-mail]>
Cc: Deepak Gupta <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Liam Howlett <[e-mail]>
Cc: Lorenzo Stoakes <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Cc: Palmer Dabbelt <[e-mail]>
Cc: Paul Walmsley <[e-mail]>
Cc: Peter Xu <[e-mail]>
Cc: Rob Herring <[e-mail]>
Cc: Suren Baghdasaryan <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Yuanchu Xie <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

fs/userfaultfd.c

···
 	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) {
···
 	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)

include/asm-generic/pgtable_uffd.h

···
 #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)
 {

include/linux/mm_inline.h

···
 
 	return dstm;
 }
-#endif
 
 /*
  * If this pte is wr-protected by uffd-wp in any form, arm the special pte to
···
 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;
+
+	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)));
···
 			   make_pte_marker(PTE_MARKER_UFFD_WP));
 		return true;
 	}
-#endif
+
 	return false;
 }
 
···
 
 	return true;
 }
+#endif
 
 /**
  * num_pages_contiguous() - determine the number of contiguous pages

include/linux/userfaultfd_k.h

···
 	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) ||
···
 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);
+}
+
+/*
+ * 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 (pte_present(pte))
+		return false;
+
+	if (pte_swp_uffd_wp(pte))
+		return true;
+
+	if (pte_is_uffd_wp_marker(pte))
+		return true;
+
+	return false;
+}
 #else /* CONFIG_USERFAULTFD */
 
 /* mm helpers */
···
 	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);
+	return false;
 }
 
 /*
···
  */
 static inline bool pte_swp_uffd_wp_any(pte_t pte)
 {
-#ifdef CONFIG_PTE_MARKER_UFFD_WP
-	if (pte_present(pte))
-		return false;
-	if (pte_swp_uffd_wp(pte))
-		return true;
-
-	if (pte_is_uffd_wp_marker(pte))
-		return true;
-#endif
 	return false;
 }
-
+#endif /* CONFIG_USERFAULTFD */
 #endif /* _LINUX_USERFAULTFD_K_H */

mm/memory.c

···
 {
 	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;
···
 		pte++;
 		addr += PAGE_SIZE;
 	}
-#endif
+
 	return was_installed;
 }