selftests/mm: skip hugepage-mremap test if userfaultfd unavailable

Gracefully skip test if userfaultfd is not supported (ENOSYS) or not
permitted (EPERM), instead of failing.  This avoids misleading failures
with clear skip messages.

--------------
Before Patch
--------------
~ running ./hugepage-mremap
...
~ Bail out! userfaultfd: Function not implemented
~ Planned tests != run tests (1 != 0)
~ Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
~ [FAIL]
not ok 4 hugepage-mremap # exit=1

--------------
After Patch
--------------
~ running ./hugepage-mremap
...
~ ok 2 # SKIP userfaultfd is not supported/not enabled.
~ 1 skipped test(s) detected.
~ Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0
~ [SKIP]
ok 4 hugepage-mremap # SKIP

Link: https://lkml.kernel.org/r/20250816040113.760010-8-aboorvad@linux.ibm.com
Co-developed-by: Donet Tom <donettom@linux.ibm.com>
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 13 insertions, 3 deletions

diff --git a/tools/testing/selftests/mm/hugepage-mremap.c b/tools/testing/selftests/mm/hugepage-mremap.c
index c463d1c09c9b..2bd1dac75c3f 100644
--- a/tools/testing/selftests/mm/hugepage-mremap.c
+++ b/tools/testing/selftests/mm/hugepage-mremap.c
@@ -65,10 +65,20 @@ static void register_region_with_uffd(char *addr, size_t len)
 	struct uffdio_api uffdio_api;
 
 	/* Create and enable userfaultfd object. */
-
 	uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
-	if (uffd == -1)
-		ksft_exit_fail_msg("userfaultfd: %s\n", strerror(errno));
+	if (uffd == -1) {
+		switch (errno) {
+		case EPERM:
+			ksft_exit_skip("Insufficient permissions, try running as root.\n");
+			break;
+		case ENOSYS:
+			ksft_exit_skip("userfaultfd is not supported/not enabled.\n");
+			break;
+		default:
+			ksft_exit_fail_msg("userfaultfd failed with %s\n", strerror(errno));
+			break;
+		}
+	}
 
 	uffdio_api.api = UFFD_API;
 	uffdio_api.features = 0;