Prefault, especially with RW, makes the GUP test too easy, and may not yet
reach the core of the test.
For example, R/O longterm pins will just hit, pte_write()==true for
whatever cases, the unsharing logic won't be ever tested.
This patch remove the prefault. This tortures more code paths at least to
cover the unshare care for R/O longterm pins, in which case the first R/O
GUP attempt will fault in the page R/O first, then the 2nd will go through
the unshare path, checking whether an unshare is needed.
Cc: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
tools/testing/selftests/mm/gup_longterm.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/mm/gup_longterm.c b/tools/testing/selftests/mm/gup_longterm.c
index ad168d35b23b..488e32186246 100644
--- a/tools/testing/selftests/mm/gup_longterm.c
+++ b/tools/testing/selftests/mm/gup_longterm.c
@@ -119,10 +119,16 @@ static void do_test(int fd, size_t size, enum test_type type, bool shared)
}
/*
- * Fault in the page writable such that GUP-fast can eventually pin
- * it immediately.
+ * Explicitly avoid pre-faulting in the page, this can help testing
+ * more code paths.
+ *
+ * Take example of an upcoming R/O pin test, if we RW prefault the
+ * page, such pin will directly skip R/O unsharing and the longterm
+ * pin will success mostly always. When not prefaulted, R/O
+ * longterm pin will first fault in a RO page, then the 2nd round
+ * it'll go via the unshare check. Otherwise those paths aren't
+ * covered.
*/
- memset(mem, 0, size);
switch (type) {
case TEST_TYPE_RO:
--
2.44.0
