[PATCH mm-unstable v1 03/20] selftests/vm: cow: R/O long-term pinning reliability tests for non-anon pages

David Hildenbrand
2022-11-16T10:30:10Z

Let's test whether R/O long-term pinning is reliable for non-anonymous
memory: when R/O long-term pinning a page, the expectation is that we
break COW early before pinning, such that actual write access via the
page tables won't break COW later and end up replacing the R/O-pinned
page in the page table.

Consequently, R/O long-term pinning in private mappings would only target
exclusive anonymous pages.

For now, all tests fail:
# [RUN] R/O longterm GUP pin ... with shared zeropage
not ok 151 Longterm R/O pin is reliable
# [RUN] R/O longterm GUP pin ... with memfd
not ok 152 Longterm R/O pin is reliable
# [RUN] R/O longterm GUP pin ... with tmpfile
not ok 153 Longterm R/O pin is reliable
# [RUN] R/O longterm GUP pin ... with huge zeropage
not ok 154 Longterm R/O pin is reliable
# [RUN] R/O longterm GUP pin ... with memfd hugetlb (2048 kB)
not ok 155 Longterm R/O pin is reliable
# [RUN] R/O longterm GUP pin ... with memfd hugetlb (1048576 kB)
not ok 156 Longterm R/O pin is reliable
# [RUN] R/O longterm GUP-fast pin ... with shared zeropage
not ok 157 Longterm R/O pin is reliable
# [RUN] R/O longterm GUP-fast pin ... with memfd
not ok 158 Longterm R/O pin is reliable
# [RUN] R/O longterm GUP-fast pin ... with tmpfile
not ok 159 Longterm R/O pin is reliable
# [RUN] R/O longterm GUP-fast pin ... with huge zeropage
not ok 160 Longterm R/O pin is reliable
# [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (2048 kB)
not ok 161 Longterm R/O pin is reliable
# [RUN] R/O longterm GUP-fast pin ... with memfd hugetlb (1048576 kB)
not ok 162 Longterm R/O pin is reliable

Signed-off-by: David Hildenbrand <david@redhat.com>
---
tools/testing/selftests/vm/cow.c | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vm/cow.c b/tools/testing/selftests/vm/cow.c
index fb07bd44529c..73e05b52c49e 100644
--- a/tools/testing/selftests/vm/cow.c
+++ b/tools/testing/selftests/vm/cow.c
@@ -561,6 +561,7 @@ static void test_iouring_fork(char *mem, size_t size)
#endif /* LOCAL_CONFIG_HAVE_LIBURING */

enum ro_pin_test {
+ RO_PIN_TEST,
RO_PIN_TEST_SHARED,
RO_PIN_TEST_PREVIOUSLY_SHARED,
RO_PIN_TEST_RO_EXCLUSIVE,
@@ -593,6 +594,8 @@ static void do_test_ro_pin(char *mem, size_t size, enum ro_pin_test test,
}

switch (test) {
+ case RO_PIN_TEST:
+ break;
case RO_PIN_TEST_SHARED:
case RO_PIN_TEST_PREVIOUSLY_SHARED:
/*
@@ -1193,6 +1196,16 @@ static void test_cow(char *mem, const char *smem, size_t size)
free(old);
}

+static void test_ro_pin(char *mem, const char *smem, size_t size)
+{
+ do_test_ro_pin(mem, size, RO_PIN_TEST, false);
+}
+
+static void test_ro_fast_pin(char *mem, const char *smem, size_t size)
+{
+ do_test_ro_pin(mem, size, RO_PIN_TEST, true);
+}
+
static void run_with_zeropage(non_anon_test_fn fn, const char *desc)
{
char *mem, *smem, tmp;
@@ -1433,7 +1446,7 @@ struct non_anon_test_case {
};

/*
- * Test cases that target any pages in private mappings that are non anonymous:
+ * Test cases that target any pages in private mappings that are not anonymous:
* pages that may get shared via COW ndependent of fork(). This includes
* the shared zeropage(s), pagecache pages, ...
*/
@@ -1446,6 +1459,19 @@ static const struct non_anon_test_case non_anon_test_cases[] = {
"Basic COW",
test_cow,
},
+ /*
+ * Take a R/O longterm pin. When modifying the page via the page table,
+ * the page content change must be visible via the pin.
+ */
+ {
+ "R/O longterm GUP pin",
+ test_ro_pin,
+ },
+ /* Same as above, but using GUP-fast. */
+ {
+ "R/O longterm GUP-fast pin",
+ test_ro_fast_pin,
+ },
};

static void run_non_anon_test_case(struct non_anon_test_case const *test_case)
--
2.38.1