selftests/mm: add uffd unit test for UFFDIO_POISON

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.

Link: https://lkml.kernel.org/r/20230707215540.2324998-9-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Gaosheng Cui <cuigaosheng1@huawei.com>
Cc: Huang, Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Jan Alexander Steffens (heftig) <heftig@archlinux.org>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nadav Amit <namit@vmware.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: T.J. Alumbaugh <talumbau@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: ZhangPeng <zhangpeng362@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
index 04d91f1..2709a34 100644 (file)
--- 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)