From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>

hugetlb-shm and thuge-gen tests require that limits defined by
/proc/sys/kernel/{shmmax,shmall} should be higher than certain values.

Add helpers that allow setting these limits and restoring their settings on
a test exit.

They will be used later in hugetlb-shm and thuge-gen.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 tools/testing/selftests/mm/vm_util.c | 28 ++++++++++++++++++++++++++++
 tools/testing/selftests/mm/vm_util.h |  9 +++++++++
 2 files changed, 37 insertions(+)

diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index 752566f75c0b..5a89c2d903be 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -761,3 +761,31 @@ void write_num(const char *path, unsigned long num)
 	sprintf(buf, "%lu", num);
 	write_file(path, buf, strlen(buf) + 1);
 }
+
+static unsigned long shmall, shmmax;
+
+void __shm_limits_restore(void)
+{
+	if (shmmax)
+		write_num("/proc/sys/kernel/shmmax", shmmax);
+	if (shmall)
+		write_num("/proc/sys/kernel/shmall", shmall);
+}
+
+void shm_limits_prepare(unsigned long length)
+{
+	unsigned long nr = length / psize();
+	unsigned long val;
+
+	val = read_num("/proc/sys/kernel/shmmax");
+	if (val < length) {
+		write_num("/proc/sys/kernel/shmmax", length);
+		shmmax = val;
+	}
+
+	val = read_num("/proc/sys/kernel/shmall");
+	if (val < nr) {
+		write_num("/proc/sys/kernel/shmall", nr);
+		shmall = val;
+	}
+}
diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 5fc9707f6b9a..ea8fc8fdf0eb 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -168,3 +168,12 @@ void write_file(const char *path, const char *buf, size_t buflen);
 int read_file(const char *path, char *buf, size_t buflen);
 unsigned long read_num(const char *path);
 void write_num(const char *path, unsigned long num);
+
+void shm_limits_prepare(unsigned long length);
+void __shm_limits_restore(void);
+
+#define SHM_LIMITS_RESTORE()						\
+static void __attribute__((destructor)) shm_limits_restore(void)	\
+{									\
+	__shm_limits_restore();						\
+}
-- 
2.53.0