selftests/mm: add userfaultfd RWP tests

Coverage for UFFDIO_REGISTER_MODE_RWP and UFFDIO_RWPROTECT:

  rwp-async          async mode — touch pages, verify permissions are
                     auto-restored without a message
  rwp-sync           sync mode — access blocks, handler resolves via
                     UFFDIO_RWPROTECT
  rwp-pagemap        PAGEMAP_SCAN reports still-cold pages via
                     inverted PAGE_IS_ACCESSED
  rwp-mprotect       RWP survives mprotect(PROT_NONE) ->
                     mprotect(PROT_READ|PROT_WRITE) round-trip
  rwp-gup            GUP walks through a protnone RWP PTE (pipe
                     write/read drives the GUP path)
  rwp-async-toggle   UFFDIO_SET_MODE flips between sync and async
                     without re-registering
  rwp-close          closing the uffd restores page permissions
  rwp-fork           RWP survives fork() with EVENT_FORK; child's
                     PTEs keep the uffd bit
  rwp-fork-pin       RWP survives fork() on an RO-longterm-pinned
                     anon page (forces copy_present_page()); child
                     read auto-resolves and clears the bit, proving
                     PAGE_NONE was in place
  rwp-wp-exclusive   register with MODE_WP|MODE_RWP returns -EINVAL

All tests run against anon, shmem, shmem-private, hugetlb, and
hugetlb-private memory, except rwp-fork-pin which is anon-only —
copy_present_page() is the private-anon pinned-exclusive fork path.

Snapshot the RWP additions into tools/include/uapi/linux/userfaultfd.h so
the selftest builds without requiring "make headers" first, matching the
mechanism established by commit 580ea358af0a ("selftests/mm: fix
additional build errors for selftests").

Link: https://lore.kernel.org/ak-Z9KO2mP9HMOPW@thinkstation
Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Assisted-by: Claude:claude-opus-4-6
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
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.howlett@oracle.com>
Cc: Lorenzo Stoakes <ljs@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>

1 files changed, 50 insertions, 4 deletions

diff --git a/tools/include/uapi/linux/userfaultfd.h b/tools/include/uapi/linux/userfaultfd.h
index 4283de22d5b6..c8e99df95219 100644
--- a/tools/include/uapi/linux/userfaultfd.h
+++ b/tools/include/uapi/linux/userfaultfd.h
@@ -25,7 +25,8 @@
 #define UFFD_API ((__u64)0xAA)
 #define UFFD_API_REGISTER_MODES (UFFDIO_REGISTER_MODE_MISSING |	\
 				 UFFDIO_REGISTER_MODE_WP |	\
-				 UFFDIO_REGISTER_MODE_MINOR)
+				 UFFDIO_REGISTER_MODE_MINOR |	\
+				 UFFDIO_REGISTER_MODE_RWP)
 #define UFFD_API_FEATURES (UFFD_FEATURE_PAGEFAULT_FLAG_WP |	\
 			   UFFD_FEATURE_EVENT_FORK |		\
 			   UFFD_FEATURE_EVENT_REMAP |		\
@@ -42,10 +43,13 @@
 			   UFFD_FEATURE_WP_UNPOPULATED |	\
 			   UFFD_FEATURE_POISON |		\
 			   UFFD_FEATURE_WP_ASYNC |		\
-			   UFFD_FEATURE_MOVE)
+			   UFFD_FEATURE_MOVE |			\
+			   UFFD_FEATURE_RWP |			\
+			   UFFD_FEATURE_RWP_ASYNC)
 #define UFFD_API_IOCTLS				\
 	((__u64)1 << _UFFDIO_REGISTER |		\
 	 (__u64)1 << _UFFDIO_UNREGISTER |	\
+	 (__u64)1 << _UFFDIO_SET_MODE |		\
 	 (__u64)1 << _UFFDIO_API)
 #define UFFD_API_RANGE_IOCTLS			\
 	((__u64)1 << _UFFDIO_WAKE |		\
@@ -54,13 +58,15 @@
 	 (__u64)1 << _UFFDIO_MOVE |		\
 	 (__u64)1 << _UFFDIO_WRITEPROTECT |	\
 	 (__u64)1 << _UFFDIO_CONTINUE |		\
-	 (__u64)1 << _UFFDIO_POISON)
+	 (__u64)1 << _UFFDIO_POISON |		\
+	 (__u64)1 << _UFFDIO_RWPROTECT)
 #define UFFD_API_RANGE_IOCTLS_BASIC		\
 	((__u64)1 << _UFFDIO_WAKE |		\
 	 (__u64)1 << _UFFDIO_COPY |		\
 	 (__u64)1 << _UFFDIO_WRITEPROTECT |	\
 	 (__u64)1 << _UFFDIO_CONTINUE |		\
-	 (__u64)1 << _UFFDIO_POISON)
+	 (__u64)1 << _UFFDIO_POISON |		\
+	 (__u64)1 << _UFFDIO_RWPROTECT)
 
 /*
  * Valid ioctl command number range with this API is from 0x00 to
@@ -79,6 +85,8 @@
 #define _UFFDIO_WRITEPROTECT		(0x06)
 #define _UFFDIO_CONTINUE		(0x07)
 #define _UFFDIO_POISON			(0x08)
+#define _UFFDIO_RWPROTECT		(0x09)
+#define _UFFDIO_SET_MODE		(0x0A)
 #define _UFFDIO_API			(0x3F)
 
 /* userfaultfd ioctl ids */
@@ -103,6 +111,10 @@
 				      struct uffdio_continue)
 #define UFFDIO_POISON		_IOWR(UFFDIO, _UFFDIO_POISON, \
 				      struct uffdio_poison)
+#define UFFDIO_RWPROTECT	_IOWR(UFFDIO, _UFFDIO_RWPROTECT,	\
+				      struct uffdio_rwprotect)
+#define UFFDIO_SET_MODE		_IOW(UFFDIO, _UFFDIO_SET_MODE,	\
+				     struct uffdio_set_mode)
 
 /* read() structure */
 struct uffd_msg {
@@ -158,6 +170,7 @@ struct uffd_msg {
 #define UFFD_PAGEFAULT_FLAG_WRITE	(1<<0)	/* If this was a write fault */
 #define UFFD_PAGEFAULT_FLAG_WP		(1<<1)	/* If reason is VM_UFFD_WP */
 #define UFFD_PAGEFAULT_FLAG_MINOR	(1<<2)	/* If reason is VM_UFFD_MINOR */
+#define UFFD_PAGEFAULT_FLAG_RWP		(1<<3)	/* If reason is VM_UFFD_RWP */
 
 struct uffdio_api {
 	/* userland asks for an API number and the features to enable */
@@ -230,6 +243,18 @@ struct uffdio_api {
 	 *
 	 * UFFD_FEATURE_MOVE indicates that the kernel supports moving an
 	 * existing page contents from userspace.
+	 *
+	 * UFFD_FEATURE_RWP indicates that the kernel supports
+	 * UFFDIO_REGISTER_MODE_RWP for read-write protection tracking.
+	 * Pages are made inaccessible via UFFDIO_RWPROTECT and faults
+	 * are delivered when the pages are re-accessed.
+	 *
+	 * UFFD_FEATURE_RWP_ASYNC indicates asynchronous mode for
+	 * UFFDIO_REGISTER_MODE_RWP.  When set, faults on read-write
+	 * protected pages are auto-resolved by the kernel (PTE
+	 * permissions restored immediately) without delivering a message
+	 * to the userfaultfd handler.  Use PAGEMAP_SCAN with inverted
+	 * PAGE_IS_ACCESSED to find pages that were not re-accessed.
 	 */
 #define UFFD_FEATURE_PAGEFAULT_FLAG_WP		(1<<0)
 #define UFFD_FEATURE_EVENT_FORK			(1<<1)
@@ -248,6 +273,8 @@ struct uffdio_api {
 #define UFFD_FEATURE_POISON			(1<<14)
 #define UFFD_FEATURE_WP_ASYNC			(1<<15)
 #define UFFD_FEATURE_MOVE			(1<<16)
+#define UFFD_FEATURE_RWP			(1<<17)
+#define UFFD_FEATURE_RWP_ASYNC			(1<<18)
 	__u64 features;
 
 	__u64 ioctls;
@@ -263,6 +290,7 @@ struct uffdio_register {
 #define UFFDIO_REGISTER_MODE_MISSING	((__u64)1<<0)
 #define UFFDIO_REGISTER_MODE_WP		((__u64)1<<1)
 #define UFFDIO_REGISTER_MODE_MINOR	((__u64)1<<2)
+#define UFFDIO_REGISTER_MODE_RWP	((__u64)1<<3)
 	__u64 mode;
 
 	/*
@@ -356,6 +384,14 @@ struct uffdio_poison {
 	__s64 updated;
 };
 
+struct uffdio_rwprotect {
+	struct uffdio_range range;
+	/* !RWP means undo RWP-protection */
+#define UFFDIO_RWPROTECT_MODE_RWP		((__u64)1<<0)
+#define UFFDIO_RWPROTECT_MODE_DONTWAKE		((__u64)1<<1)
+	__u64 mode;
+};
+
 struct uffdio_move {
 	__u64 dst;
 	__u64 src;
@@ -374,6 +410,16 @@ struct uffdio_move {
 	__s64 move;
 };
 
+struct uffdio_set_mode {
+	/*
+	 * Toggle async mode for features at runtime.
+	 * Supported: UFFD_FEATURE_RWP_ASYNC.
+	 * Setting a bit in both enable and disable is invalid.
+	 */
+	__u64 enable;
+	__u64 disable;
+};
+
 /*
  * Flags for the userfaultfd(2) system call itself.
  */