[PATCH v3 8/8] selftests/mm: add uffd unit test for UFFDIO_POISON

Axel Rasmussen
2023-07-06T22:51:57Z

The test is pretty basic, and exercises UFFDIO_POISON straightforwardly.
We register a region with userfaultfd, in missing fault mode. For each
fault, we either UFFDIO_COPY a zeroed page (odd pages) or UFFDIO_POISON
(even pages). We do this mix to test "something like a real use case",
where guest memory would be some mix of poisoned and non-poisoned pages.

We read each page in the region, and assert that the odd pages are
zeroed as expected, and the even pages yield a SIGBUS as expected.

Why UFFDIO_COPY instead of UFFDIO_ZEROPAGE? Because hugetlb doesn't
support UFFDIO_ZEROPAGE, and we don't want to have special case code.

Acked-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
---
tools/testing/selftests/mm/uffd-unit-tests.c | 117 +++++++++++++++++++
1 file changed, 117 insertions(+)

diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
index 04d91f144d1c..2709a34a39c5 100644
--- a/tools/testing/selftests/mm/uffd-unit-tests.c
+++ b/tools/testing/selftests/mm/uffd-unit-tests.c
@@ -951,6 +951,117 @@ static void uffd_zeropage_test(uffd_test_args_t *args)
uffd_test_pass();
}

+static void uffd_register_poison(int uffd, void *addr, uint64_t len)
+{
+ uint64_t ioctls = 0;
+ uint64_t expected = (1 << _UFFDIO_COPY) | (1 << _UFFDIO_POISON);
+
+ if (uffd_register_with_ioctls(uffd, addr, len, true,
+ false, false, &ioctls))
+ err("poison register fail");
+
+ if ((ioctls & expected) != expected)
+ err("registered area doesn't support COPY and POISON ioctls");
+}
+
+static void do_uffdio_poison(int uffd, unsigned long offset)
+{
+ struct uffdio_poison uffdio_poison = { 0 };
+ int ret;
+ __s64 res;
+
+ uffdio_poison.range.start = (unsigned long) area_dst + offset;
+ uffdio_poison.range.len = page_size;
+ uffdio_poison.mode = 0;
+ ret = ioctl(uffd, UFFDIO_POISON, &uffdio_poison);
+ res = uffdio_poison.updated;
+
+ if (ret)
+ err("UFFDIO_POISON error: %"PRId64, (int64_t)res);
+ else if (res != page_size)
+ err("UFFDIO_POISON unexpected size: %"PRId64, (int64_t)res);
+}
+
+static void uffd_poison_handle_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 | UFFD_PAGEFAULT_FLAG_MINOR))
+ err("unexpected fault type %llu", msg->arg.pagefault.flags);
+
+ offset = (char *)(unsigned long)msg->arg.pagefault.address - area_dst;
+ offset &= ~(page_size-1);
+
+ /* Odd pages -> copy zeroed page; even pages -> poison. */
+ if (offset & page_size)
+ copy_page(uffd, offset, false);
+ else
+ do_uffdio_poison(uffd, offset);
+}
+
+static void uffd_poison_test(uffd_test_args_t *targs)
+{
+ pthread_t uffd_mon;
+ char c;
+ struct uffd_args args = { 0 };
+ struct sigaction act = { 0 };
+ unsigned long nr_sigbus = 0;
+ unsigned long nr;
+
+ fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
+
+ uffd_register_poison(uffd, area_dst, nr_pages * page_size);
+ memset(area_src, 0, nr_pages * page_size);
+
+ args.handle_fault = uffd_poison_handle_fault;
+ if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args))
+ err("uffd_poll_thread create");
+
+ sigbuf = &jbuf;
+ act.sa_sigaction = sighndl;
+ act.sa_flags = SA_SIGINFO;
+ if (sigaction(SIGBUS, &act, 0))
+ err("sigaction");
+
+ for (nr = 0; nr < nr_pages; ++nr) {
+ unsigned long offset = nr * page_size;
+ const char *bytes = (const char *) area_dst + offset;
+ const char *i;
+
+ if (sigsetjmp(*sigbuf, 1)) {
+ /*
+ * Access below triggered a SIGBUS, which was caught by
+ * sighndl, which then jumped here. Count this SIGBUS,
+ * and move on to next page.
+ */
+ ++nr_sigbus;
+ continue;
+ }
+
+ for (i = bytes; i < bytes + page_size; ++i) {
+ if (*i)
+ err("nonzero byte in area_dst (%p) at %p: %u",
+ area_dst, i, *i);
+ }
+ }
+
+ if (write(pipefd[1], &c, sizeof(c)) != sizeof(c))
+ err("pipe write");
+ if (pthread_join(uffd_mon, NULL))
+ err("pthread_join()");
+
+ if (nr_sigbus != nr_pages / 2)
+ err("expected to receive %lu SIGBUS, actually received %lu",
+ nr_pages / 2, nr_sigbus);
+
+ uffd_test_pass();
+}
+
/*
* Test the returned uffdio_register.ioctls with different register modes.
* Note that _UFFDIO_ZEROPAGE is tested separately in the zeropage test.
@@ -1126,6 +1237,12 @@ uffd_test_case_t uffd_tests[] = {
UFFD_FEATURE_PAGEFAULT_FLAG_WP |
UFFD_FEATURE_WP_HUGETLBFS_SHMEM,
},
+ {
+ .name = "poison",
+ .uffd_fn = uffd_poison_test,
+ .mem_targets = MEM_ALL,
+ .uffd_feature_required = UFFD_FEATURE_POISON,
+ },
};

static void usage(const char *prog)
--
2.41.0.255.g8b1d071c50-goog