mm: update uffd-stress to handle EINVAL for unset config features

Now that we have updated userfaultfd_api to correctly return EINVAL when a
feature is requested but not available, let's fix the uffd-stress test to
only set the UFFD_FEATURE_WP_UNPOPULATED feature when the config is set. 
In addition, still run the test if the CONFIG_PTE_MARKER_UFFD_WP is not
set, just dont use the corresponding UFFD_FEATURE_WP_UNPOPULATED feature.

Link: https://lkml.kernel.org/r/20240626130513.120193-2-audra@redhat.comSigned-off-by: Audra Mitchell <audra@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rafael Aquini <raquini@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/uffd-stress.c

@@ -36,6 +36,8 @@
 #include <asm-generic/unistd.h>
 #include "uffd-common.h"
 
+uint64_t features;
+
 #define BOUNCE_RANDOM		(1<<0)
 #define BOUNCE_RACINGFAULTS	(1<<1)
 #define BOUNCE_VERIFY		(1<<2)
@@ -245,10 +247,14 @@ static int userfaultfd_stress(void)
 	unsigned long nr;
 	struct uffd_args args[nr_cpus];
 	uint64_t mem_size = nr_pages * page_size;
+	int flags = 0;
 
 	memset(args, 0, sizeof(struct uffd_args) * nr_cpus);
 
-	if (uffd_test_ctx_init(UFFD_FEATURE_WP_UNPOPULATED, NULL))
+	if (features & UFFD_FEATURE_WP_UNPOPULATED && test_type == TEST_ANON)
+		flags = UFFD_FEATURE_WP_UNPOPULATED;
+
+	if (uffd_test_ctx_init(flags, NULL))
 		err("context init failed");
 
 	if (posix_memalign(&area, page_size, page_size))
@@ -383,8 +389,6 @@ static void set_test_type(const char *type)
 
 static void parse_test_type_arg(const char *raw_type)
 {
-	uint64_t features = UFFD_API_FEATURES;
-
 	set_test_type(raw_type);
 
 	if (!test_type)
@@ -407,8 +411,8 @@ static void parse_test_type_arg(const char *raw_type)
 	 * feature.
 	 */
 
-	if (userfaultfd_open(&features))
-		err("Userfaultfd open failed");
+	if (uffd_get_features(&features))
+		err("failed to get available features");
 
 	test_uffdio_wp = test_uffdio_wp &&
 		(features & UFFD_FEATURE_PAGEFAULT_FLAG_WP);