[PATCH 13/14] selftests/mm: add userfaultfd RWP tests

Kiryl Shutsemau (Meta)
2026-04-27T11:48:01Z

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.

Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Assisted-by: Claude:claude-opus-4-6
---
tools/testing/selftests/mm/uffd-unit-tests.c | 734 +++++++++++++++++++
1 file changed, 734 insertions(+)

diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
index 6f5e404a446c..6fdfe8bc3a70 100644
--- a/tools/testing/selftests/mm/uffd-unit-tests.c
+++ b/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -7,6 +7,7 @@

#include "uffd-common.h"

+#include <linux/fs.h>
#include "../../../../mm/gup_test.h"

#ifdef __NR_userfaultfd
@@ -167,6 +168,23 @@ static int test_uffd_api(bool use_dev)
goto out;
}

+ /* Verify returned fd-level ioctls bitmask */
+ {
+ uint64_t expected_ioctls =
+ BIT_ULL(_UFFDIO_REGISTER) |
+ BIT_ULL(_UFFDIO_UNREGISTER) |
+ BIT_ULL(_UFFDIO_API) |
+ BIT_ULL(_UFFDIO_SET_MODE);
+
+ if ((uffdio_api.ioctls & expected_ioctls) != expected_ioctls) {
+ uffd_test_fail("UFFDIO_API missing expected ioctls: "
+ "got=0x%"PRIx64", expected=0x%"PRIx64,
+ (uint64_t)uffdio_api.ioctls,
+ expected_ioctls);
+ goto out;
+ }
+ }
+
/* Test double requests of UFFDIO_API with a random feature set */
uffdio_api.features = BIT_ULL(0);
if (ioctl(uffd, UFFDIO_API, &uffdio_api) == 0) {
@@ -623,6 +641,653 @@ void uffd_minor_collapse_test(uffd_global_test_opts_t *gopts, uffd_test_args_t *
uffd_minor_test_common(gopts, true, false);
}

+static int uffd_register_rwp(int uffd, void *addr, uint64_t len)
+{
+ struct uffdio_register reg = {
+ .range = { .start = (unsigned long)addr, .len = len },
+ .mode = UFFDIO_REGISTER_MODE_RWP,
+ };
+
+ if (ioctl(uffd, UFFDIO_REGISTER, &reg) == -1)
+ return -errno;
+ return 0;
+}
+
+static void rwprotect_range(int uffd, __u64 start, __u64 len, bool protect)
+{
+ struct uffdio_rwprotect rwp = {
+ .range = { .start = start, .len = len },
+ .mode = protect ? UFFDIO_RWPROTECT_MODE_RWP : 0,
+ };
+
+ if (ioctl(uffd, UFFDIO_RWPROTECT, &rwp))
+ err("UFFDIO_RWPROTECT failed");
+}
+
+static void set_async_mode(int uffd, bool enable)
+{
+ struct uffdio_set_mode mode = { };
+
+ if (enable)
+ mode.enable = UFFD_FEATURE_RWP_ASYNC;
+ else
+ mode.disable = UFFD_FEATURE_RWP_ASYNC;
+
+ if (ioctl(uffd, UFFDIO_SET_MODE, &mode))
+ err("UFFDIO_SET_MODE failed");
+}
+
+/*
+ * Test async RWP faults on anonymous memory.
+ * Populate pages, register MODE_RWP with RWP_ASYNC,
+ * RW-protect, re-access, verify content preserved and no faults delivered.
+ */
+static void uffd_rwp_async_test(uffd_global_test_opts_t *gopts,
+ uffd_test_args_t *args)
+{
+ unsigned long nr_pages = gopts->nr_pages;
+ unsigned long page_size = gopts->page_size;
+ unsigned long p;
+
+ /* Populate all pages with known content */
+ for (p = 0; p < nr_pages; p++)
+ memset(gopts->area_dst + p * page_size, p % 255 + 1, page_size);
+
+ /* Register MODE_RWP */
+ if (uffd_register_rwp(gopts->uffd, gopts->area_dst,
+ nr_pages * page_size))
+ err("register failure");
+
+ /* RW-protect all pages (sets protnone) */
+ rwprotect_range(gopts->uffd, (uint64_t)gopts->area_dst,
+ nr_pages * page_size, true);
+
+ /* Access all pages — should auto-resolve, no faults */
+ for (p = 0; p < nr_pages; p++) {
+ unsigned char *page = (unsigned char *)gopts->area_dst +
+ p * page_size;
+ unsigned char expected = p % 255 + 1;
+
+ if (page[0] != expected) {
+ uffd_test_fail("page %lu content mismatch: %u != %u",
+ p, page[0], expected);
+ return;
+ }
+ }
+
+ uffd_test_pass();
+}
+
+/*
+ * Fault handler for RWP — unprotect the page via UFFDIO_RWPROTECT.
+ */
+static void uffd_handle_rwp_fault(uffd_global_test_opts_t *gopts,
+ struct uffd_msg *msg,
+ struct uffd_args *uargs)
+{
+ if (!(msg->arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_RWP))
+ err("expected RWP fault, got 0x%llx",
+ msg->arg.pagefault.flags);
+
+ rwprotect_range(gopts->uffd, msg->arg.pagefault.address,
+ gopts->page_size, false);
+ uargs->minor_faults++;
+}
+
+/*
+ * Test sync RWP faults on anonymous memory.
+ * Populate pages, register MODE_RWP (sync), RW-protect,
+ * access from worker thread, verify fault delivered, UFFDIO_RWPROTECT resolves.
+ */
+static void uffd_rwp_sync_test(uffd_global_test_opts_t *gopts,
+ uffd_test_args_t *args)
+{
+ unsigned long nr_pages = gopts->nr_pages;
+ unsigned long page_size = gopts->page_size;
+ pthread_t uffd_mon;
+ struct uffd_args uargs = { };
+ char c = '\0';
+ unsigned long p;
+
+ uargs.gopts = gopts;
+ uargs.handle_fault = uffd_handle_rwp_fault;
+
+ /* Populate all pages */
+ for (p = 0; p < nr_pages; p++)
+ memset(gopts->area_dst + p * page_size, p % 255 + 1, page_size);
+
+ /* Register MODE_RWP */
+ if (uffd_register_rwp(gopts->uffd, gopts->area_dst,
+ nr_pages * page_size))
+ err("register failure");
+
+ /* RW-protect all pages */
+ rwprotect_range(gopts->uffd, (uint64_t)gopts->area_dst,
+ nr_pages * page_size, true);
+
+ /* Start fault handler thread */
+ if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &uargs))
+ err("uffd_poll_thread create");
+
+ /* Access all pages — triggers sync RWP faults, handler unprotects */
+ for (p = 0; p < nr_pages; p++) {
+ unsigned char *page = (unsigned char *)gopts->area_dst +
+ p * page_size;
+
+ if (page[0] != (p % 255 + 1)) {
+ uffd_test_fail("page %lu content mismatch", p);
+ goto out;
+ }
+ }
+
+ if (uargs.minor_faults == 0) {
+ uffd_test_fail("expected RWP faults, got 0");
+ goto out;
+ }
+
+ uffd_test_pass();
+out:
+ if (write(gopts->pipefd[1], &c, sizeof(c)) != sizeof(c))
+ err("pipe write");
+ if (pthread_join(uffd_mon, NULL))
+ err("join() failed");
+}
+
+/*
+ * Test PAGEMAP_SCAN detection of RW-protected (cold) pages.
+ */
+static void uffd_rwp_pagemap_test(uffd_global_test_opts_t *gopts,
+ uffd_test_args_t *args)
+{
+ unsigned long nr_pages = gopts->nr_pages;
+ unsigned long page_size = gopts->page_size;
+ unsigned long p;
+ struct page_region regions[16];
+ struct pm_scan_arg pm_arg;
+ int pagemap_fd;
+ long ret;
+
+ /* Need at least 4 pages */
+ if (nr_pages < 4) {
+ uffd_test_skip("need at least 4 pages");
+ return;
+ }
+
+ /* Populate all pages */
+ for (p = 0; p < nr_pages; p++)
+ memset(gopts->area_dst + p * page_size, 0xab, page_size);
+
+ /* Register and RW-protect */
+ if (uffd_register_rwp(gopts->uffd, gopts->area_dst,
+ nr_pages * page_size))
+ err("register failure");
+
+ rwprotect_range(gopts->uffd, (uint64_t)gopts->area_dst,
+ nr_pages * page_size, true);
+
+ /* Touch first half of pages to re-activate them (async auto-resolve) */
+ for (p = 0; p < nr_pages / 2; p++) {
+ volatile char *page = gopts->area_dst + p * page_size;
+ (void)*page;
+ }
+
+ /* Scan for cold (still RW-protected) pages */
+ pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+ if (pagemap_fd < 0)
+ err("open pagemap");
+
+ /*
+ * PAGE_IS_ACCESSED is set once the uffd-wp bit has been cleared
+ * (access happened, or the user resolved). Invert it to select
+ * still-protected (cold) pages.
+ */
+ memset(&pm_arg, 0, sizeof(pm_arg));
+ pm_arg.size = sizeof(pm_arg);
+ pm_arg.start = (uint64_t)gopts->area_dst;
+ pm_arg.end = (uint64_t)gopts->area_dst + nr_pages * page_size;
+ pm_arg.vec = (uint64_t)regions;
+ pm_arg.vec_len = 16;
+ pm_arg.category_mask = PAGE_IS_ACCESSED;
+ pm_arg.category_inverted = PAGE_IS_ACCESSED;
+ pm_arg.return_mask = PAGE_IS_ACCESSED;
+
+ ret = ioctl(pagemap_fd, PAGEMAP_SCAN, &pm_arg);
+ close(pagemap_fd);
+
+ if (ret < 0) {
+ uffd_test_fail("PAGEMAP_SCAN failed: %s", strerror(errno));
+ return;
+ }
+
+ /*
+ * The second half of pages should be reported as RW-protected.
+ * They may be coalesced into one region.
+ */
+ if (ret < 1) {
+ uffd_test_fail("expected cold pages, got %ld regions", ret);
+ return;
+ }
+
+ /* Verify the cold region covers the second half */
+ uint64_t cold_start = regions[0].start;
+ uint64_t expected_start = (uint64_t)gopts->area_dst +
+ (nr_pages / 2) * page_size;
+
+ if (cold_start != expected_start) {
+ uffd_test_fail("cold region starts at 0x%lx, expected 0x%lx",
+ (unsigned long)cold_start,
+ (unsigned long)expected_start);
+ return;
+ }
+
+ uffd_test_pass();
+}
+
+/*
+ * Test that RWP protection survives a mprotect(PROT_NONE) ->
+ * mprotect(PROT_READ|PROT_WRITE) round-trip. The uffd-wp bit on a
+ * VM_UFFD_RWP VMA must continue to carry PROT_NONE semantics after
+ * mprotect() changes the base protection; otherwise accesses would
+ * silently succeed and the pagemap bit would stick without a fault
+ * ever clearing it.
+ */
+static void uffd_rwp_mprotect_test(uffd_global_test_opts_t *gopts,
+ uffd_test_args_t *args)
+{
+ unsigned long nr_pages = gopts->nr_pages;
+ unsigned long page_size = gopts->page_size;
+ unsigned long p;
+ struct page_region regions[16];
+ struct pm_scan_arg pm_arg;
+ int pagemap_fd;
+ long ret;
+
+ /* Populate all pages */
+ for (p = 0; p < nr_pages; p++)
+ memset(gopts->area_dst + p * page_size, 0xab, page_size);
+
+ /* Register and RW-protect the whole range */
+ if (uffd_register_rwp(gopts->uffd, gopts->area_dst,
+ nr_pages * page_size))
+ err("register failure");
+ rwprotect_range(gopts->uffd, (uint64_t)gopts->area_dst,
+ nr_pages * page_size, true);
+
+ /* Round-trip mprotect(): PROT_NONE -> PROT_READ|PROT_WRITE */
+ if (mprotect(gopts->area_dst, nr_pages * page_size, PROT_NONE))
+ err("mprotect() PROT_NONE");
+ if (mprotect(gopts->area_dst, nr_pages * page_size,
+ PROT_READ | PROT_WRITE))
+ err("mprotect() PROT_READ|PROT_WRITE");
+
+ /* Touch every page. Async RWP must auto-resolve each fault. */
+ for (p = 0; p < nr_pages; p++) {
+ volatile char *page = gopts->area_dst + p * page_size;
+ (void)*page;
+ }
+
+ /*
+ * After touching, no page should remain RW-protected. A stuck
+ * uffd-wp bit would mean mprotect() silently dropped PROT_NONE and
+ * the access never faulted.
+ */
+ pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+ if (pagemap_fd < 0)
+ err("open pagemap");
+
+ memset(&pm_arg, 0, sizeof(pm_arg));
+ pm_arg.size = sizeof(pm_arg);
+ pm_arg.start = (uint64_t)gopts->area_dst;
+ pm_arg.end = (uint64_t)gopts->area_dst + nr_pages * page_size;
+ pm_arg.vec = (uint64_t)regions;
+ pm_arg.vec_len = 16;
+ pm_arg.category_mask = PAGE_IS_ACCESSED;
+ pm_arg.category_inverted = PAGE_IS_ACCESSED;
+ pm_arg.return_mask = PAGE_IS_ACCESSED;
+
+ ret = ioctl(pagemap_fd, PAGEMAP_SCAN, &pm_arg);
+ close(pagemap_fd);
+
+ if (ret < 0) {
+ uffd_test_fail("PAGEMAP_SCAN failed: %s", strerror(errno));
+ return;
+ }
+ if (ret != 0) {
+ uffd_test_fail("expected no cold pages after mprotect()+touch, got %ld regions",
+ ret);
+ return;
+ }
+
+ uffd_test_pass();
+}
+
+/*
+ * Test that GUP resolves through protnone PTEs (async mode).
+ * RW-protect pages, then use a pipe to exercise GUP on the RW-protected
+ * memory. write() from RW-protected pages triggers GUP which must fault
+ * through the protnone PTE.
+ */
+static void uffd_rwp_gup_test(uffd_global_test_opts_t *gopts,
+ uffd_test_args_t *args)
+{
+ unsigned long page_size = gopts->page_size;
+ char *buf;
+ int pipefd[2];
+
+ buf = malloc(page_size);
+ if (!buf)
+ err("malloc");
+
+ /* Populate first page with known content */
+ memset(gopts->area_dst, 0xCD, page_size);
+
+ if (uffd_register_rwp(gopts->uffd, gopts->area_dst, page_size))
+ err("register failure");
+
+ rwprotect_range(gopts->uffd, (uint64_t)gopts->area_dst, page_size, true);
+
+ if (pipe(pipefd))
+ err("pipe");
+
+ /*
+ * write() from the RW-protected page into the pipe.
+ * This triggers GUP on the protnone PTE. In async mode the
+ * kernel auto-restores permissions and GUP succeeds.
+ */
+ /*
+ * Use base page size for write — hugetlb pages are larger than
+ * the default pipe buffer, which would deadlock.
+ */
+ if (write(pipefd[1], gopts->area_dst, getpagesize()) != getpagesize()) {
+ uffd_test_fail("write from RW-protected page failed: %s",
+ strerror(errno));
+ goto out;
+ }
+
+ if (read(pipefd[0], buf, getpagesize()) != getpagesize()) {
+ uffd_test_fail("read from pipe failed");
+ goto out;
+ }
+
+ if (memcmp(buf, "\xCD", 1) != 0) {
+ uffd_test_fail("content mismatch: got 0x%02x, expected 0xCD",
+ (unsigned char)buf[0]);
+ goto out;
+ }
+
+ uffd_test_pass();
+out:
+ close(pipefd[0]);
+ close(pipefd[1]);
+ free(buf);
+}
+
+/*
+ * Test runtime toggle between async and sync modes.
+ * Start in async mode (detection), flip to sync (eviction), verify faults
+ * block, resolve them, flip back to async.
+ */
+static void uffd_rwp_async_toggle_test(uffd_global_test_opts_t *gopts,
+ uffd_test_args_t *args)
+{
+ unsigned long nr_pages = gopts->nr_pages;
+ unsigned long page_size = gopts->page_size;
+ struct uffd_args uargs = { };
+ pthread_t uffd_mon;
+ char c = '\0';
+ unsigned long p;
+
+ uargs.gopts = gopts;
+ uargs.handle_fault = uffd_handle_rwp_fault;
+
+ /* Populate */
+ for (p = 0; p < nr_pages; p++)
+ memset(gopts->area_dst + p * page_size, p % 255 + 1, page_size);
+
+ if (uffd_register_rwp(gopts->uffd, gopts->area_dst,
+ nr_pages * page_size))
+ err("register failure");
+
+ /* Phase 1: async detection — RW-protect, access first half */
+ rwprotect_range(gopts->uffd, (uint64_t)gopts->area_dst,
+ nr_pages * page_size, true);
+
+ for (p = 0; p < nr_pages / 2; p++) {
+ volatile char *page = gopts->area_dst + p * page_size;
+ (void)*page; /* auto-resolves in async mode */
+ }
+
+ /* Phase 2: flip to sync for eviction */
+ set_async_mode(gopts->uffd, false);
+
+ /* Start handler — will receive faults for cold pages */
+ if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &uargs))
+ err("uffd_poll_thread create");
+
+ /* Access second half (cold pages) — should trigger sync faults */
+ for (p = nr_pages / 2; p < nr_pages; p++) {
+ unsigned char *page = (unsigned char *)gopts->area_dst +
+ p * page_size;
+ if (page[0] != (p % 255 + 1)) {
+ uffd_test_fail("page %lu content mismatch", p);
+ goto out;
+ }
+ }
+
+ if (uargs.minor_faults == 0) {
+ uffd_test_fail("expected sync faults, got 0");
+ goto out;
+ }
+
+ /* Phase 3: flip back to async */
+ set_async_mode(gopts->uffd, true);
+
+ /* RW-protect and access again — should auto-resolve */
+ rwprotect_range(gopts->uffd, (uint64_t)gopts->area_dst,
+ nr_pages * page_size, true);
+
+ for (p = 0; p < nr_pages; p++) {
+ volatile char *page = gopts->area_dst + p * page_size;
+ (void)*page;
+ }
+
+ uffd_test_pass();
+out:
+ if (write(gopts->pipefd[1], &c, sizeof(c)) != sizeof(c))
+ err("pipe write");
+ if (pthread_join(uffd_mon, NULL))
+ err("join() failed");
+}
+
+/*
+ * Test that RW-protected pages become accessible after closing uffd.
+ */
+static void uffd_rwp_close_test(uffd_global_test_opts_t *gopts,
+ uffd_test_args_t *args)
+{
+ unsigned long nr_pages = gopts->nr_pages;
+ unsigned long page_size = gopts->page_size;
+ unsigned long p;
+
+ /* Populate */
+ for (p = 0; p < nr_pages; p++)
+ memset(gopts->area_dst + p * page_size, p % 255 + 1, page_size);
+
+ if (uffd_register_rwp(gopts->uffd, gopts->area_dst,
+ nr_pages * page_size))
+ err("register failure");
+
+ rwprotect_range(gopts->uffd, (uint64_t)gopts->area_dst,
+ nr_pages * page_size, true);
+
+ /* Close uffd — should restore protnone PTEs */
+ close(gopts->uffd);
+ gopts->uffd = -1;
+
+ /* All pages should be accessible with original content */
+ for (p = 0; p < nr_pages; p++) {
+ unsigned char *page = (unsigned char *)gopts->area_dst +
+ p * page_size;
+ unsigned char expected = p % 255 + 1;
+
+ if (page[0] != expected) {
+ uffd_test_fail("page %lu not accessible after close", p);
+ return;
+ }
+ }
+
+ uffd_test_pass();
+}
+
+/*
+ * Test that RWP protection is preserved across fork() when
+ * UFFD_FEATURE_EVENT_FORK is enabled. Without preservation, the child's
+ * PTEs would lose the uffd-wp marker and RWP-protected accesses would
+ * silently fall through to do_numa_page().
+ */
+static void uffd_rwp_fork_test(uffd_global_test_opts_t *gopts,
+ uffd_test_args_t *args)
+{
+ unsigned long nr_pages = gopts->nr_pages;
+ unsigned long page_size = gopts->page_size;
+ int pagemap_fd;
+ uint64_t value;
+
+ if (uffd_register_rwp(gopts->uffd, gopts->area_dst,
+ nr_pages * page_size))
+ err("register failed");
+
+ /* Populate + RWP-protect */
+ *gopts->area_dst = 1;
+ rwprotect_range(gopts->uffd, (uint64_t)gopts->area_dst,
+ page_size, true);
+
+ /* Parent: verify uffd-wp bit is set before fork */
+ pagemap_fd = pagemap_open();
+ value = pagemap_get_entry(pagemap_fd, gopts->area_dst);
+ pagemap_check_wp(value, true);
+
+ /*
+ * Fork with EVENT_FORK: child inherits VM_UFFD_RWP. Child reads
+ * its own pagemap and must still see the uffd-wp bit set.
+ */
+ if (pagemap_test_fork(gopts, true, false)) {
+ uffd_test_fail("RWP marker lost in child after fork");
+ goto out;
+ }
+
+ uffd_test_pass();
+out:
+ close(pagemap_fd);
+}
+
+/*
+ * Test that RWP protection on a pinned anon page is preserved across fork().
+ * Pinning forces copy_present_page() in the child path, which must restore
+ * PAGE_NONE on top of the uffd bit. Using async mode, a read in the child
+ * auto-resolves if — and only if — the PTE was actually protnone+uffd; the
+ * cleared uffd bit afterward proves the fault path ran.
+ */
+static void uffd_rwp_fork_pin_test(uffd_global_test_opts_t *gopts,
+ uffd_test_args_t *args)
+{
+ unsigned long page_size = gopts->page_size;
+ pin_args pin_args = {};
+ int pagemap_fd, status;
+ uint64_t value;
+ pid_t child;
+
+ if (uffd_register_rwp(gopts->uffd, gopts->area_dst, page_size))
+ err("register failed");
+
+ /* Populate. */
+ *gopts->area_dst = 1;
+
+ /* RO-longterm pin so fork() takes copy_present_page() for this PTE. */
+ if (pin_pages(&pin_args, gopts->area_dst, page_size)) {
+ uffd_test_skip("Possibly CONFIG_GUP_TEST missing or unprivileged");
+ uffd_unregister(gopts->uffd, gopts->area_dst, page_size);
+ return;
+ }
+
+ /* RWP-protect: PTE is now PAGE_NONE + uffd bit. */
+ rwprotect_range(gopts->uffd, (uint64_t)gopts->area_dst, page_size, true);
+
+ pagemap_fd = pagemap_open();
+ value = pagemap_get_entry(pagemap_fd, gopts->area_dst);
+ pagemap_check_wp(value, true);
+
+ child = fork();
+ if (child < 0)
+ err("fork");
+ if (child == 0) {
+ volatile char c;
+ int cfd;
+
+ /*
+ * Read the pinned page. Only reaches the fault path if the
+ * child PTE is protnone + uffd; async mode auto-resolves and
+ * clears the uffd bit. If copy_present_page() dropped
+ * PAGE_NONE, the read would silently succeed and the bit
+ * would still be set.
+ */
+ c = *(volatile char *)gopts->area_dst;
+ (void)c;
+
+ cfd = pagemap_open();
+ value = pagemap_get_entry(cfd, gopts->area_dst);
+ close(cfd);
+ _exit((value & PM_UFFD_WP) ? 1 : 0);
+ }
+ if (waitpid(child, &status, 0) < 0)
+ err("waitpid");
+
+ unpin_pages(&pin_args);
+ close(pagemap_fd);
+ if (uffd_unregister(gopts->uffd, gopts->area_dst, page_size))
+ err("unregister failed");
+
+ if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+ uffd_test_fail("RWP not enforced in child after pinned fork");
+ return;
+ }
+
+ uffd_test_pass();
+}
+
+/*
+ * Test WP and RWP coexisting on the same VMA (async RWP mode).
+ * Register with MODE_WP | MODE_RWP, apply WP, then apply RWP, then read
+ * pages. Async RWP auto-resolves, and the WP bit must survive the RWP
+ * protect/unprotect cycle so subsequent writes still deliver WP faults.
+ */
+/*
+ * WP and RWP share the uffd-wp PTE bit and cannot coexist in the same VMA.
+ * Registration requesting both modes must be rejected.
+ */
+static void uffd_rwp_wp_exclusive_test(uffd_global_test_opts_t *gopts,
+ uffd_test_args_t *args)
+{
+ unsigned long nr_pages = gopts->nr_pages;
+ unsigned long page_size = gopts->page_size;
+ struct uffdio_register reg = { };
+
+ reg.range.start = (unsigned long)gopts->area_dst;
+ reg.range.len = nr_pages * page_size;
+ reg.mode = UFFDIO_REGISTER_MODE_WP | UFFDIO_REGISTER_MODE_RWP;
+
+ if (ioctl(gopts->uffd, UFFDIO_REGISTER, &reg) == 0) {
+ uffd_test_fail("register with WP|RWP unexpectedly succeeded");
+ return;
+ }
+ if (errno != EINVAL) {
+ uffd_test_fail("register with WP|RWP: expected EINVAL, got %d",
+ errno);
+ return;
+ }
+ uffd_test_pass();
+}
+
static sigjmp_buf jbuf, *sigbuf;

static void sighndl(int sig, siginfo_t *siginfo, void *ptr)
@@ -1625,6 +2290,75 @@ uffd_test_case_t uffd_tests[] = {
/* We can't test MADV_COLLAPSE, so try our luck */
.uffd_feature_required = UFFD_FEATURE_MINOR_SHMEM,
},
+ {
+ .name = "rwp-async",
+ .uffd_fn = uffd_rwp_async_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required =
+ UFFD_FEATURE_RWP | UFFD_FEATURE_RWP_ASYNC,
+ },
+ {
+ .name = "rwp-sync",
+ .uffd_fn = uffd_rwp_sync_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required = UFFD_FEATURE_RWP,
+ },
+ {
+ .name = "rwp-pagemap",
+ .uffd_fn = uffd_rwp_pagemap_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required =
+ UFFD_FEATURE_RWP | UFFD_FEATURE_RWP_ASYNC,
+ },
+ {
+ .name = "rwp-mprotect",
+ .uffd_fn = uffd_rwp_mprotect_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required =
+ UFFD_FEATURE_RWP | UFFD_FEATURE_RWP_ASYNC,
+ },
+ {
+ .name = "rwp-gup",
+ .uffd_fn = uffd_rwp_gup_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required =
+ UFFD_FEATURE_RWP | UFFD_FEATURE_RWP_ASYNC,
+ },
+ {
+ .name = "rwp-async-toggle",
+ .uffd_fn = uffd_rwp_async_toggle_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required =
+ UFFD_FEATURE_RWP | UFFD_FEATURE_RWP_ASYNC,
+ },
+ {
+ .name = "rwp-close",
+ .uffd_fn = uffd_rwp_close_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required = UFFD_FEATURE_RWP,
+ },
+ {
+ .name = "rwp-fork",
+ .uffd_fn = uffd_rwp_fork_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required =
+ UFFD_FEATURE_RWP | UFFD_FEATURE_EVENT_FORK,
+ },
+ {
+ .name = "rwp-fork-pin",
+ .uffd_fn = uffd_rwp_fork_pin_test,
+ .mem_targets = MEM_ANON,
+ .uffd_feature_required =
+ UFFD_FEATURE_RWP | UFFD_FEATURE_RWP_ASYNC,
+ },
+ {
+ .name = "rwp-wp-exclusive",
+ .uffd_fn = uffd_rwp_wp_exclusive_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required =
+ UFFD_FEATURE_RWP |
+ UFFD_FEATURE_PAGEFAULT_FLAG_WP,
+ },
{
.name = "sigbus",
.uffd_fn = uffd_sigbus_test,
--
2.51.2