selftests/mm: split uffd tests into uffd-stress and uffd-unit-tests

In many ways it's weird and unwanted to keep all the tests in the same
userfaultfd.c at least when still in the current way.

For example, it doesn't make much sense to run the stress test for each
method we can create an userfaultfd handle (either via syscall or /dev/
node).  It's a waste of time running this twice for the whole stress as
the stress paths are the same, only the open path is different.

It's also just weird to need to manually specify different types of memory
to run all unit tests for the userfaultfd interface.  We should be able to
just run a single program and that should go through all functional uffd
tests without running the stress test at all.  The stress test was more
for torturing and finding race conditions.  We don't want to wait for
stress to finish just to regress test a functional test.

When we start to pile up more things on top of the same file and same
functions, things start to go a bit chaos and the code is just harder to
maintain too with tons of global variables.

This patch creates a new test uffd-unit-tests to keep userfaultfd unit
tests in the future, currently empty.

Meanwhile rename the old userfaultfd.c test to uffd-stress.c.

Link: https://lkml.kernel.org/r/20230412164244.328270-1-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/.gitignore

@@ -21,7 +21,8 @@ protection_keys
 protection_keys_32
 protection_keys_64
 madv_populate
-userfaultfd
+uffd-stress
+uffd-unit-tests
 mlock-intersect-test
 mlock-random-test
 virtual_address_range

tools/testing/selftests/mm/Makefile

@@ -20,7 +20,7 @@ MACHINE ?= $(shell echo $(uname_M) | sed -e 's/aarch64.*/arm64/' -e 's/ppc64.*/p
 # Avoid accidental wrong builds, due to built-in rules working just a little
 # bit too well--but not quite as well as required for our situation here.
 #
-# In other words, "make userfaultfd" is supposed to fail to build at all,
+# In other words, "make $SOME_TEST" is supposed to fail to build at all,
 # because this Makefile only supports either "make" (all), or "make /full/path".
 # However,  the built-in rules, if not suppressed, will pick up CFLAGS and the
 # initial LDLIBS (but not the target-specific LDLIBS, because those are only
@@ -57,7 +57,8 @@ TEST_GEN_PROGS += mremap_test
 TEST_GEN_PROGS += on-fault-limit
 TEST_GEN_PROGS += thuge-gen
 TEST_GEN_PROGS += transhuge-stress
-TEST_GEN_PROGS += userfaultfd
+TEST_GEN_PROGS += uffd-stress
+TEST_GEN_PROGS += uffd-unit-tests
 TEST_GEN_PROGS += soft-dirty
 TEST_GEN_PROGS += split_huge_page_test
 TEST_GEN_PROGS += ksm_tests
@@ -108,7 +109,8 @@ include ../lib.mk
 
 $(TEST_GEN_PROGS): vm_util.c
 
-$(OUTPUT)/userfaultfd: uffd-common.c
+$(OUTPUT)/uffd-stress: uffd-common.c
+$(OUTPUT)/uffd-unit-tests: uffd-common.c
 
 ifeq ($(MACHINE),x86_64)
 BINARIES_32 := $(patsubst %,$(OUTPUT)/%,$(BINARIES_32))

tools/testing/selftests/mm/run_vmtests.sh

@@ -196,14 +196,16 @@ CATEGORY="gup_test" run_test ./gup_test -a
 # Dump pages 0, 19, and 4096, using pin_user_pages:
 CATEGORY="gup_test" run_test ./gup_test -ct -F 0x1 0 19 0x1000
 
+CATEGORY="userfaultfd" run_test ./uffd-unit-tests
 uffd_mods=("" ":dev")
+uffd_stress_bin=./uffd-stress
 for mod in "${uffd_mods[@]}"; do
-	CATEGORY="userfaultfd" run_test ./userfaultfd anon${mod} 20 16
+	CATEGORY="userfaultfd" run_test ${uffd_stress_bin} anon${mod} 20 16
 	# Hugetlb tests require source and destination huge pages. Pass in half
 	# the size ($half_ufd_size_MB), which is used for *each*.
-	CATEGORY="userfaultfd" run_test ./userfaultfd hugetlb${mod} "$half_ufd_size_MB" 32
-	CATEGORY="userfaultfd" run_test ./userfaultfd hugetlb_shared${mod} "$half_ufd_size_MB" 32
-	CATEGORY="userfaultfd" run_test ./userfaultfd shmem${mod} 20 16
+	CATEGORY="userfaultfd" run_test ${uffd_stress_bin} hugetlb${mod} "$half_ufd_size_MB" 32
+	CATEGORY="userfaultfd" run_test ${uffd_stress_bin} hugetlb_shared${mod} "$half_ufd_size_MB" 32
+	CATEGORY="userfaultfd" run_test ${uffd_stress_bin} shmem${mod} 20 16
 done
 
 #cleanup

tools/testing/selftests/mm/uffd-unit-tests.c

@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Userfaultfd unit tests.
+ *
+ *  Copyright (C) 2015-2023  Red Hat, Inc.
+ */
+
+#include "uffd-common.h"
+
+#ifdef __NR_userfaultfd
+
+int main(int argc, char *argv[])
+{
+	return KSFT_PASS;
+}
+
+#else /* __NR_userfaultfd */
+
+#warning "missing __NR_userfaultfd definition"
+
+int main(void)
+{
+	printf("Skipping %s (missing __NR_userfaultfd)\n", __file__);
+	return KSFT_SKIP;
+}
+
+#endif /* __NR_userfaultfd */