[v4,8/8] selftests/mm: add uffd unit test for UFFDIO_POISON

Commit Message

Axel Rasmussen July 7, 2023, 9:55 p.m. UTC

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 <[e-mail]>
Signed-off-by: Axel Rasmussen <[e-mail]>
---
 tools/testing/selftests/mm/uffd-unit-tests.c | 117 +++++++++++++++++++
 1 file changed, 117 insertions(+)

Comments

Ryan Roberts Sept. 21, 2023, 4:28 p.m. UTC | #1

On 07/07/2023 22:55, Axel Rasmussen wrote:
> 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 <[e-mail]>
> Signed-off-by: Axel Rasmussen <[e-mail]>

Hi,

FYI, when running this test on arm64 it provokes a kernel panic. I've posted a
fix along with a detailed explanation at [1].

[1]
https://lore.kernel.org/linux-arm-kernel/[e-mail]/

Thanks,
Ryan

Patch

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)