selftests/mm: don't fail if pagemap_scan isn't supported

This change allows to run tests on old kernels.

Link: https://lkml.kernel.org/r/20231117181127.2574897-1-avagin@google.com
Reported-by: Ryan Roberts <ryan.roberts@arm.com>
Closes: https://lore.kernel.org/lkml/696a0a99-eb42-4e13-be14-58a88c9c33f7@arm.com/
Signed-off-by: Andrei Vagin <avagin@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index ec3478b96e4c9192280e87819f1753110acefdb5..4aeb8d5299ffd3ffbca10e64dd60437ddce5ebb9 100644 (file)
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -29,15 +29,13 @@ uint64_t pagemap_get_entry(int fd, char *start)
        return entry;
 }
 
-static uint64_t pagemap_scan_get_categories(int fd, char *start)
+static uint64_t __pagemap_scan_get_categories(int fd, char *start, struct page_region *r)
 {
        struct pm_scan_arg arg;
-       struct page_region r;
-       long ret;
 
        arg.start = (uintptr_t)start;
        arg.end = (uintptr_t)(start + psize());
-       arg.vec = (uintptr_t)&r;
+       arg.vec = (uintptr_t)r;
        arg.vec_len = 1;
        arg.flags = 0;
        arg.size = sizeof(struct pm_scan_arg);
@@ -49,7 +47,15 @@ static uint64_t pagemap_scan_get_categories(int fd, char *start)
                                  PAGE_IS_HUGE | PAGE_IS_SOFT_DIRTY;
        arg.return_mask = arg.category_anyof_mask;
 
-       ret = ioctl(fd, PAGEMAP_SCAN, &arg);
+       return ioctl(fd, PAGEMAP_SCAN, &arg);
+}
+
+static uint64_t pagemap_scan_get_categories(int fd, char *start)
+{
+       struct page_region r;
+       long ret;
+
+       ret = __pagemap_scan_get_categories(fd, start, &r);
        if (ret < 0)
                ksft_exit_fail_msg("PAGEMAP_SCAN failed: %s\n", strerror(errno));
        if (ret == 0)
@@ -57,18 +63,39 @@ static uint64_t pagemap_scan_get_categories(int fd, char *start)
        return r.categories;
 }
 
+/* `start` is any valid address. */
+static bool pagemap_scan_supported(int fd, char *start)
+{
+       static int supported = -1;
+       int ret;
+
+       if (supported != -1)
+               return supported;
+
+       /* Provide an invalid address in order to trigger EFAULT. */
+       ret = __pagemap_scan_get_categories(fd, start, (struct page_region *) ~0UL);
+       if (ret == 0)
+               ksft_exit_fail_msg("PAGEMAP_SCAN succedded unexpectedly\n");
+
+       supported = errno == EFAULT;
+
+       return supported;
+}
+
 static bool page_entry_is(int fd, char *start, char *desc,
                          uint64_t pagemap_flags, uint64_t pagescan_flags)
 {
-       bool m, s;
+       bool m = pagemap_get_entry(fd, start) & pagemap_flags;
 
-       m = pagemap_get_entry(fd, start) & pagemap_flags;
-       s = pagemap_scan_get_categories(fd, start) & pagescan_flags;
-       if (m == s)
-               return m;
+       if (pagemap_scan_supported(fd, start)) {
+               bool s = pagemap_scan_get_categories(fd, start) & pagescan_flags;
 
-       ksft_exit_fail_msg(
-               "read and ioctl return unmatched results for %s: %d %d", desc, m, s);
+               if (m == s)
+                       return m;
+
+               ksft_exit_fail_msg(
+                       "read and ioctl return unmatched results for %s: %d %d", desc, m, s);
+       }
        return m;
 }