aboutsummaryrefslogtreecommitdiffstatshomepage
path: root/tools/testing/selftests/mm/uffd-common.c
diff options
context:
space:
mode:
Diffstat (limited to 'tools/testing/selftests/mm/uffd-common.c')
-rw-r--r--tools/testing/selftests/mm/uffd-common.c715
1 files changed, 715 insertions, 0 deletions
diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c
new file mode 100644
index 000000000000..b0ac0ec2356d
--- /dev/null
+++ b/tools/testing/selftests/mm/uffd-common.c
@@ -0,0 +1,715 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Userfaultfd tests util functions
+ *
+ * Copyright (C) 2015-2023 Red Hat, Inc.
+ */
+
+#include "uffd-common.h"
+
+#define BASE_PMD_ADDR ((void *)(1UL << 30))
+
+volatile bool test_uffdio_copy_eexist = true;
+unsigned long nr_cpus, nr_pages, nr_pages_per_cpu, page_size;
+char *area_src, *area_src_alias, *area_dst, *area_dst_alias, *area_remap;
+int uffd = -1, uffd_flags, finished, *pipefd, test_type;
+bool map_shared;
+bool test_uffdio_wp = true;
+unsigned long long *count_verify;
+uffd_test_ops_t *uffd_test_ops;
+uffd_test_case_ops_t *uffd_test_case_ops;
+
+static int uffd_mem_fd_create(off_t mem_size, bool hugetlb)
+{
+ unsigned int memfd_flags = 0;
+ int mem_fd;
+
+ if (hugetlb)
+ memfd_flags = MFD_HUGETLB;
+ mem_fd = memfd_create("uffd-test", memfd_flags);
+ if (mem_fd < 0)
+ err("memfd_create");
+ if (ftruncate(mem_fd, mem_size))
+ err("ftruncate");
+ if (fallocate(mem_fd,
+ FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0,
+ mem_size))
+ err("fallocate");
+
+ return mem_fd;
+}
+
+static void anon_release_pages(char *rel_area)
+{
+ if (madvise(rel_area, nr_pages * page_size, MADV_DONTNEED))
+ err("madvise(MADV_DONTNEED) failed");
+}
+
+static int anon_allocate_area(void **alloc_area, bool is_src)
+{
+ *alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
+ MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+ if (*alloc_area == MAP_FAILED) {
+ *alloc_area = NULL;
+ return -errno;
+ }
+ return 0;
+}
+
+static void noop_alias_mapping(__u64 *start, size_t len, unsigned long offset)
+{
+}
+
+static void hugetlb_release_pages(char *rel_area)
+{
+ if (!map_shared) {
+ if (madvise(rel_area, nr_pages * page_size, MADV_DONTNEED))
+ err("madvise(MADV_DONTNEED) failed");
+ } else {
+ if (madvise(rel_area, nr_pages * page_size, MADV_REMOVE))
+ err("madvise(MADV_REMOVE) failed");
+ }
+}
+
+static int hugetlb_allocate_area(void **alloc_area, bool is_src)
+{
+ off_t size = nr_pages * page_size;
+ off_t offset = is_src ? 0 : size;
+ void *area_alias = NULL;
+ char **alloc_area_alias;
+ int mem_fd = uffd_mem_fd_create(size * 2, true);
+
+ *alloc_area = mmap(NULL, size, PROT_READ | PROT_WRITE,
+ (map_shared ? MAP_SHARED : MAP_PRIVATE) |
+ (is_src ? 0 : MAP_NORESERVE),
+ mem_fd, offset);
+ if (*alloc_area == MAP_FAILED) {
+ *alloc_area = NULL;
+ return -errno;
+ }
+
+ if (map_shared) {
+ area_alias = mmap(NULL, size, PROT_READ | PROT_WRITE,
+ MAP_SHARED, mem_fd, offset);
+ if (area_alias == MAP_FAILED)
+ return -errno;
+ }
+
+ if (is_src) {
+ alloc_area_alias = &area_src_alias;
+ } else {
+ alloc_area_alias = &area_dst_alias;
+ }
+ if (area_alias)
+ *alloc_area_alias = area_alias;
+
+ close(mem_fd);
+ return 0;
+}
+
+static void hugetlb_alias_mapping(__u64 *start, size_t len, unsigned long offset)
+{
+ if (!map_shared)
+ return;
+
+ *start = (unsigned long) area_dst_alias + offset;
+}
+
+static void shmem_release_pages(char *rel_area)
+{
+ if (madvise(rel_area, nr_pages * page_size, MADV_REMOVE))
+ err("madvise(MADV_REMOVE) failed");
+}
+
+static int shmem_allocate_area(void **alloc_area, bool is_src)
+{
+ void *area_alias = NULL;
+ size_t bytes = nr_pages * page_size, hpage_size = read_pmd_pagesize();
+ unsigned long offset = is_src ? 0 : bytes;
+ char *p = NULL, *p_alias = NULL;
+ int mem_fd = uffd_mem_fd_create(bytes * 2, false);
+
+ /* TODO: clean this up. Use a static addr is ugly */
+ p = BASE_PMD_ADDR;
+ if (!is_src)
+ /* src map + alias + interleaved hpages */
+ p += 2 * (bytes + hpage_size);
+ p_alias = p;
+ p_alias += bytes;
+ p_alias += hpage_size; /* Prevent src/dst VMA merge */
+
+ *alloc_area = mmap(p, bytes, PROT_READ | PROT_WRITE, MAP_SHARED,
+ mem_fd, offset);
+ if (*alloc_area == MAP_FAILED) {
+ *alloc_area = NULL;
+ return -errno;
+ }
+ if (*alloc_area != p)
+ err("mmap of memfd failed at %p", p);
+
+ area_alias = mmap(p_alias, bytes, PROT_READ | PROT_WRITE, MAP_SHARED,
+ mem_fd, offset);
+ if (area_alias == MAP_FAILED) {
+ munmap(*alloc_area, bytes);
+ *alloc_area = NULL;
+ return -errno;
+ }
+ if (area_alias != p_alias)
+ err("mmap of anonymous memory failed at %p", p_alias);
+
+ if (is_src)
+ area_src_alias = area_alias;
+ else
+ area_dst_alias = area_alias;
+
+ close(mem_fd);
+ return 0;
+}
+
+static void shmem_alias_mapping(__u64 *start, size_t len, unsigned long offset)
+{
+ *start = (unsigned long)area_dst_alias + offset;
+}
+
+static void shmem_check_pmd_mapping(void *p, int expect_nr_hpages)
+{
+ if (!check_huge_shmem(area_dst_alias, expect_nr_hpages,
+ read_pmd_pagesize()))
+ err("Did not find expected %d number of hugepages",
+ expect_nr_hpages);
+}
+
+struct uffd_test_ops anon_uffd_test_ops = {
+ .allocate_area = anon_allocate_area,
+ .release_pages = anon_release_pages,
+ .alias_mapping = noop_alias_mapping,
+ .check_pmd_mapping = NULL,
+};
+
+struct uffd_test_ops shmem_uffd_test_ops = {
+ .allocate_area = shmem_allocate_area,
+ .release_pages = shmem_release_pages,
+ .alias_mapping = shmem_alias_mapping,
+ .check_pmd_mapping = shmem_check_pmd_mapping,
+};
+
+struct uffd_test_ops hugetlb_uffd_test_ops = {
+ .allocate_area = hugetlb_allocate_area,
+ .release_pages = hugetlb_release_pages,
+ .alias_mapping = hugetlb_alias_mapping,
+ .check_pmd_mapping = NULL,
+};
+
+void uffd_stats_report(struct uffd_args *args, int n_cpus)
+{
+ int i;
+ unsigned long long miss_total = 0, wp_total = 0, minor_total = 0;
+
+ for (i = 0; i < n_cpus; i++) {
+ miss_total += args[i].missing_faults;
+ wp_total += args[i].wp_faults;
+ minor_total += args[i].minor_faults;
+ }
+
+ printf("userfaults: ");
+ if (miss_total) {
+ printf("%llu missing (", miss_total);
+ for (i = 0; i < n_cpus; i++)
+ printf("%lu+", args[i].missing_faults);
+ printf("\b) ");
+ }
+ if (wp_total) {
+ printf("%llu wp (", wp_total);
+ for (i = 0; i < n_cpus; i++)
+ printf("%lu+", args[i].wp_faults);
+ printf("\b) ");
+ }
+ if (minor_total) {
+ printf("%llu minor (", minor_total);
+ for (i = 0; i < n_cpus; i++)
+ printf("%lu+", args[i].minor_faults);
+ printf("\b)");
+ }
+ printf("\n");
+}
+
+int userfaultfd_open(uint64_t *features)
+{
+ struct uffdio_api uffdio_api;
+
+ uffd = uffd_open(UFFD_FLAGS);
+ if (uffd < 0)
+ return -1;
+ uffd_flags = fcntl(uffd, F_GETFD, NULL);
+
+ uffdio_api.api = UFFD_API;
+ uffdio_api.features = *features;
+ if (ioctl(uffd, UFFDIO_API, &uffdio_api))
+ /* Probably lack of CAP_PTRACE? */
+ return -1;
+ if (uffdio_api.api != UFFD_API)
+ err("UFFDIO_API error: %" PRIu64, (uint64_t)uffdio_api.api);
+
+ *features = uffdio_api.features;
+ return 0;
+}
+
+static inline void munmap_area(void **area)
+{
+ if (*area)
+ if (munmap(*area, nr_pages * page_size))
+ err("munmap");
+
+ *area = NULL;
+}
+
+void uffd_test_ctx_clear(void)
+{
+ size_t i;
+
+ if (pipefd) {
+ for (i = 0; i < nr_cpus * 2; ++i) {
+ if (close(pipefd[i]))
+ err("close pipefd");
+ }
+ free(pipefd);
+ pipefd = NULL;
+ }
+
+ if (count_verify) {
+ free(count_verify);
+ count_verify = NULL;
+ }
+
+ if (uffd != -1) {
+ if (close(uffd))
+ err("close uffd");
+ uffd = -1;
+ }
+
+ munmap_area((void **)&area_src);
+ munmap_area((void **)&area_src_alias);
+ munmap_area((void **)&area_dst);
+ munmap_area((void **)&area_dst_alias);
+ munmap_area((void **)&area_remap);
+}
+
+int uffd_test_ctx_init(uint64_t features, const char **errmsg)
+{
+ unsigned long nr, cpu;
+ int ret;
+
+ if (uffd_test_case_ops && uffd_test_case_ops->pre_alloc) {
+ ret = uffd_test_case_ops->pre_alloc(errmsg);
+ if (ret)
+ return ret;
+ }
+
+ ret = uffd_test_ops->allocate_area((void **)&area_src, true);
+ ret |= uffd_test_ops->allocate_area((void **)&area_dst, false);
+ if (ret) {
+ if (errmsg)
+ *errmsg = "memory allocation failed";
+ return ret;
+ }
+
+ if (uffd_test_case_ops && uffd_test_case_ops->post_alloc) {
+ ret = uffd_test_case_ops->post_alloc(errmsg);
+ if (ret)
+ return ret;
+ }
+
+ ret = userfaultfd_open(&features);
+ if (ret) {
+ if (errmsg)
+ *errmsg = "possible lack of priviledge";
+ return ret;
+ }
+
+ count_verify = malloc(nr_pages * sizeof(unsigned long long));
+ if (!count_verify)
+ err("count_verify");
+
+ for (nr = 0; nr < nr_pages; nr++) {
+ *area_mutex(area_src, nr) =
+ (pthread_mutex_t)PTHREAD_MUTEX_INITIALIZER;
+ count_verify[nr] = *area_count(area_src, nr) = 1;
+ /*
+ * In the transition between 255 to 256, powerpc will
+ * read out of order in my_bcmp and see both bytes as
+ * zero, so leave a placeholder below always non-zero
+ * after the count, to avoid my_bcmp to trigger false
+ * positives.
+ */
+ *(area_count(area_src, nr) + 1) = 1;
+ }
+
+ /*
+ * After initialization of area_src, we must explicitly release pages
+ * for area_dst to make sure it's fully empty. Otherwise we could have
+ * some area_dst pages be errornously initialized with zero pages,
+ * hence we could hit memory corruption later in the test.
+ *
+ * One example is when THP is globally enabled, above allocate_area()
+ * calls could have the two areas merged into a single VMA (as they
+ * will have the same VMA flags so they're mergeable). When we
+ * initialize the area_src above, it's possible that some part of
+ * area_dst could have been faulted in via one huge THP that will be
+ * shared between area_src and area_dst. It could cause some of the
+ * area_dst won't be trapped by missing userfaults.
+ *
+ * This release_pages() will guarantee even if that happened, we'll
+ * proactively split the thp and drop any accidentally initialized
+ * pages within area_dst.
+ */
+ uffd_test_ops->release_pages(area_dst);
+
+ pipefd = malloc(sizeof(int) * nr_cpus * 2);
+ if (!pipefd)
+ err("pipefd");
+ for (cpu = 0; cpu < nr_cpus; cpu++)
+ if (pipe2(&pipefd[cpu * 2], O_CLOEXEC | O_NONBLOCK))
+ err("pipe");
+
+ return 0;
+}
+
+void wp_range(int ufd, __u64 start, __u64 len, bool wp)
+{
+ struct uffdio_writeprotect prms;
+
+ /* Write protection page faults */
+ prms.range.start = start;
+ prms.range.len = len;
+ /* Undo write-protect, do wakeup after that */
+ prms.mode = wp ? UFFDIO_WRITEPROTECT_MODE_WP : 0;
+
+ if (ioctl(ufd, UFFDIO_WRITEPROTECT, &prms))
+ err("clear WP failed: address=0x%"PRIx64, (uint64_t)start);
+}
+
+static void continue_range(int ufd, __u64 start, __u64 len, bool wp)
+{
+ struct uffdio_continue req;
+ int ret;
+
+ req.range.start = start;
+ req.range.len = len;
+ req.mode = 0;
+ if (wp)
+ req.mode |= UFFDIO_CONTINUE_MODE_WP;
+
+ if (ioctl(ufd, UFFDIO_CONTINUE, &req))
+ err("UFFDIO_CONTINUE failed for address 0x%" PRIx64,
+ (uint64_t)start);
+
+ /*
+ * Error handling within the kernel for continue is subtly different
+ * from copy or zeropage, so it may be a source of bugs. Trigger an
+ * error (-EEXIST) on purpose, to verify doing so doesn't cause a BUG.
+ */
+ req.mapped = 0;
+ ret = ioctl(ufd, UFFDIO_CONTINUE, &req);
+ if (ret >= 0 || req.mapped != -EEXIST)
+ err("failed to exercise UFFDIO_CONTINUE error handling, ret=%d, mapped=%" PRId64,
+ ret, (int64_t) req.mapped);
+}
+
+int uffd_read_msg(int ufd, struct uffd_msg *msg)
+{
+ int ret = read(uffd, msg, sizeof(*msg));
+
+ if (ret != sizeof(*msg)) {
+ if (ret < 0) {
+ if (errno == EAGAIN || errno == EINTR)
+ return 1;
+ err("blocking read error");
+ } else {
+ err("short read");
+ }
+ }
+
+ return 0;
+}
+
+void uffd_handle_page_fault(struct uffd_msg *msg, struct uffd_args *args)
+{
+ unsigned long offset;
+
+ if (msg->event != UFFD_EVENT_PAGEFAULT)
+ err("unexpected msg event %u", msg->event);
+
+ if (msg->arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WP) {
+ /* Write protect page faults */
+ wp_range(uffd, msg->arg.pagefault.address, page_size, false);
+ args->wp_faults++;
+ } else if (msg->arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_MINOR) {
+ uint8_t *area;
+ int b;
+
+ /*
+ * Minor page faults
+ *
+ * To prove we can modify the original range for testing
+ * purposes, we're going to bit flip this range before
+ * continuing.
+ *
+ * Note that this requires all minor page fault tests operate on
+ * area_dst (non-UFFD-registered) and area_dst_alias
+ * (UFFD-registered).
+ */
+
+ area = (uint8_t *)(area_dst +
+ ((char *)msg->arg.pagefault.address -
+ area_dst_alias));
+ for (b = 0; b < page_size; ++b)
+ area[b] = ~area[b];
+ continue_range(uffd, msg->arg.pagefault.address, page_size,
+ args->apply_wp);
+ args->minor_faults++;
+ } else {
+ /*
+ * Missing page faults.
+ *
+ * Here we force a write check for each of the missing mode
+ * faults. It's guaranteed because the only threads that
+ * will trigger uffd faults are the locking threads, and
+ * their first instruction to touch the missing page will
+ * always be pthread_mutex_lock().
+ *
+ * Note that here we relied on an NPTL glibc impl detail to
+ * always read the lock type at the entry of the lock op
+ * (pthread_mutex_t.__data.__type, offset 0x10) before
+ * doing any locking operations to guarantee that. It's
+ * actually not good to rely on this impl detail because
+ * logically a pthread-compatible lib can implement the
+ * locks without types and we can fail when linking with
+ * them. However since we used to find bugs with this
+ * strict check we still keep it around. Hopefully this
+ * could be a good hint when it fails again. If one day
+ * it'll break on some other impl of glibc we'll revisit.
+ */
+ if (msg->arg.pagefault.flags & UFFD_PAGEFAULT_FLAG_WRITE)
+ err("unexpected write fault");
+
+ offset = (char *)(unsigned long)msg->arg.pagefault.address - area_dst;
+ offset &= ~(page_size-1);
+
+ if (copy_page(uffd, offset, args->apply_wp))
+ args->missing_faults++;
+ }
+}
+
+void *uffd_poll_thread(void *arg)
+{
+ struct uffd_args *args = (struct uffd_args *)arg;
+ unsigned long cpu = args->cpu;
+ struct pollfd pollfd[2];
+ struct uffd_msg msg;
+ struct uffdio_register uffd_reg;
+ int ret;
+ char tmp_chr;
+
+ if (!args->handle_fault)
+ args->handle_fault = uffd_handle_page_fault;
+
+ pollfd[0].fd = uffd;
+ pollfd[0].events = POLLIN;
+ pollfd[1].fd = pipefd[cpu*2];
+ pollfd[1].events = POLLIN;
+
+ for (;;) {
+ ret = poll(pollfd, 2, -1);
+ if (ret <= 0) {
+ if (errno == EINTR || errno == EAGAIN)
+ continue;
+ err("poll error: %d", ret);
+ }
+ if (pollfd[1].revents) {
+ if (!(pollfd[1].revents & POLLIN))
+ err("pollfd[1].revents %d", pollfd[1].revents);
+ if (read(pollfd[1].fd, &tmp_chr, 1) != 1)
+ err("read pipefd error");
+ break;
+ }
+ if (!(pollfd[0].revents & POLLIN))
+ err("pollfd[0].revents %d", pollfd[0].revents);
+ if (uffd_read_msg(uffd, &msg))
+ continue;
+ switch (msg.event) {
+ default:
+ err("unexpected msg event %u\n", msg.event);
+ break;
+ case UFFD_EVENT_PAGEFAULT:
+ args->handle_fault(&msg, args);
+ break;
+ case UFFD_EVENT_FORK:
+ close(uffd);
+ uffd = msg.arg.fork.ufd;
+ pollfd[0].fd = uffd;
+ break;
+ case UFFD_EVENT_REMOVE:
+ uffd_reg.range.start = msg.arg.remove.start;
+ uffd_reg.range.len = msg.arg.remove.end -
+ msg.arg.remove.start;
+ if (ioctl(uffd, UFFDIO_UNREGISTER, &uffd_reg.range))
+ err("remove failure");
+ break;
+ case UFFD_EVENT_REMAP:
+ area_remap = area_dst; /* save for later unmap */
+ area_dst = (char *)(unsigned long)msg.arg.remap.to;
+ break;
+ }
+ }
+
+ return NULL;
+}
+
+static void retry_copy_page(int ufd, struct uffdio_copy *uffdio_copy,
+ unsigned long offset)
+{
+ uffd_test_ops->alias_mapping(&uffdio_copy->dst,
+ uffdio_copy->len,
+ offset);
+ if (ioctl(ufd, UFFDIO_COPY, uffdio_copy)) {
+ /* real retval in ufdio_copy.copy */
+ if (uffdio_copy->copy != -EEXIST)
+ err("UFFDIO_COPY retry error: %"PRId64,
+ (int64_t)uffdio_copy->copy);
+ } else {
+ err("UFFDIO_COPY retry unexpected: %"PRId64,
+ (int64_t)uffdio_copy->copy);
+ }
+}
+
+static void wake_range(int ufd, unsigned long addr, unsigned long len)
+{
+ struct uffdio_range uffdio_wake;
+
+ uffdio_wake.start = addr;
+ uffdio_wake.len = len;
+
+ if (ioctl(ufd, UFFDIO_WAKE, &uffdio_wake))
+ fprintf(stderr, "error waking %lu\n",
+ addr), exit(1);
+}
+
+int __copy_page(int ufd, unsigned long offset, bool retry, bool wp)
+{
+ struct uffdio_copy uffdio_copy;
+
+ if (offset >= nr_pages * page_size)
+ err("unexpected offset %lu\n", offset);
+ uffdio_copy.dst = (unsigned long) area_dst + offset;
+ uffdio_copy.src = (unsigned long) area_src + offset;
+ uffdio_copy.len = page_size;
+ if (wp)
+ uffdio_copy.mode = UFFDIO_COPY_MODE_WP;
+ else
+ uffdio_copy.mode = 0;
+ uffdio_copy.copy = 0;
+ if (ioctl(ufd, UFFDIO_COPY, &uffdio_copy)) {
+ /* real retval in ufdio_copy.copy */
+ if (uffdio_copy.copy != -EEXIST)
+ err("UFFDIO_COPY error: %"PRId64,
+ (int64_t)uffdio_copy.copy);
+ wake_range(ufd, uffdio_copy.dst, page_size);
+ } else if (uffdio_copy.copy != page_size) {
+ err("UFFDIO_COPY error: %"PRId64, (int64_t)uffdio_copy.copy);
+ } else {
+ if (test_uffdio_copy_eexist && retry) {
+ test_uffdio_copy_eexist = false;
+ retry_copy_page(ufd, &uffdio_copy, offset);
+ }
+ return 1;
+ }
+ return 0;
+}
+
+int copy_page(int ufd, unsigned long offset, bool wp)
+{
+ return __copy_page(ufd, offset, false, wp);
+}
+
+int move_page(int ufd, unsigned long offset, unsigned long len)
+{
+ struct uffdio_move uffdio_move;
+
+ if (offset + len > nr_pages * page_size)
+ err("unexpected offset %lu and length %lu\n", offset, len);
+ uffdio_move.dst = (unsigned long) area_dst + offset;
+ uffdio_move.src = (unsigned long) area_src + offset;
+ uffdio_move.len = len;
+ uffdio_move.mode = UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES;
+ uffdio_move.move = 0;
+ if (ioctl(ufd, UFFDIO_MOVE, &uffdio_move)) {
+ /* real retval in uffdio_move.move */
+ if (uffdio_move.move != -EEXIST)
+ err("UFFDIO_MOVE error: %"PRId64,
+ (int64_t)uffdio_move.move);
+ wake_range(ufd, uffdio_move.dst, len);
+ } else if (uffdio_move.move != len) {
+ err("UFFDIO_MOVE error: %"PRId64, (int64_t)uffdio_move.move);
+ } else
+ return 1;
+ return 0;
+}
+
+int uffd_open_dev(unsigned int flags)
+{
+ int fd, uffd;
+
+ fd = open("/dev/userfaultfd", O_RDWR | O_CLOEXEC);
+ if (fd < 0)
+ return fd;
+ uffd = ioctl(fd, USERFAULTFD_IOC_NEW, flags);
+ close(fd);
+
+ return uffd;
+}
+
+int uffd_open_sys(unsigned int flags)
+{
+#ifdef __NR_userfaultfd
+ return syscall(__NR_userfaultfd, flags);
+#else
+ return -1;
+#endif
+}
+
+int uffd_open(unsigned int flags)
+{
+ int uffd = uffd_open_sys(flags);
+
+ if (uffd < 0)
+ uffd = uffd_open_dev(flags);
+
+ return uffd;
+}
+
+int uffd_get_features(uint64_t *features)
+{
+ struct uffdio_api uffdio_api = { .api = UFFD_API, .features = 0 };
+ /*
+ * This should by default work in most kernels; the feature list
+ * will be the same no matter what we pass in here.
+ */
+ int fd = uffd_open(UFFD_USER_MODE_ONLY);
+
+ if (fd < 0)
+ /* Maybe the kernel is older than user-only mode? */
+ fd = uffd_open(0);
+
+ if (fd < 0)
+ return fd;
+
+ if (ioctl(fd, UFFDIO_API, &uffdio_api)) {
+ close(fd);
+ return -errno;
+ }
+
+ *features = uffdio_api.features;
+ close(fd);
+
+ return 0;
+}
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.