selftests/resctrl: Split fill_buf to allow tests finer-grained control

BugLink: https://bugs.launchpad.net/bugs/2101915

[ Upstream commit f8f669699977db503569465b64dc5220ab21bb41 ]

MBM, MBA and CMT test cases call run_fill_buf() that in turn calls
fill_cache() to alloc and loop indefinitely around the buffer. This
binds buffer allocation and running the benchmark into a single bundle
so that a selftest cannot allocate a buffer once and reuse it. CAT test
doesn't want to loop around the buffer continuously and after rewrite
it needs the ability to allocate the buffer separately.

Split buffer allocation out of fill_cache() into alloc_buffer(). This
change is part of preparation for the new CAT test that allocates a
buffer and does multiple passes over the same buffer (but not in an
infinite loop).

Co-developed-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Stable-dep-of: caf02626b2bf ("selftests/resctrl: Fix memory overflow due to unhandled wraparound")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

tools/testing/selftests/resctrl/fill_buf.c

@@ -135,24 +135,34 @@ static int fill_cache_write(unsigned char *buf, size_t buf_size, bool once)
 	return 0;
 }
 
-static int fill_cache(size_t buf_size, int memflush, int op, bool once)
+static unsigned char *alloc_buffer(size_t buf_size, int memflush)
 {
 	unsigned char *buf;
-	int ret;
 
 	buf = malloc_and_init_memory(buf_size);
 	if (!buf)
-		return -1;
+		return NULL;
 
 	/* Flush the memory before using to avoid "cache hot pages" effect */
 	if (memflush)
 		mem_flush(buf, buf_size);
 
+	return buf;
+}
+
+static int fill_cache(size_t buf_size, int memflush, int op, bool once)
+{
+	unsigned char *buf;
+	int ret;
+
+	buf = alloc_buffer(buf_size, memflush);
+	if (!buf)
+		return -1;
+
 	if (op == 0)
 		ret = fill_cache_read(buf, buf_size, once);
 	else
 		ret = fill_cache_write(buf, buf_size, once);
-
 	free(buf);
 
 	if (ret) {
@@ -160,8 +170,7 @@ static int fill_cache(size_t buf_size, int memflush, int op, bool once)
 		return -1;
 	}
 
-
-	return 0;
+	return ret;
 }
 
 int run_fill_buf(size_t span, int memflush, int op, bool once)