mm/damon/dbgfs: support physical memory monitoring

This makes the 'damon-dbgfs' to support the physical memory monitoring,
in addition to the virtual memory monitoring.

Users can do the physical memory monitoring by writing a special
keyword, 'paddr' to the 'target_ids' debugfs file.  Then, DAMON will
check the special keyword and configure the monitoring context to run
with the primitives for the physical address space.

Unlike the virtual memory monitoring, the monitoring target region will
not be automatically set.  Therefore, users should also set the
monitoring target address region using the 'init_regions' debugfs file.

Also, note that the physical memory monitoring will not automatically
terminated.  The user should explicitly turn off the monitoring by
writing 'off' to the 'monitor_on' debugfs file.

Link: https://lkml.kernel.org/r/20211012205711.29216-7-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Cc: Amit Shah <amit@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rienjes <rientjes@google.com>
Cc: David Woodhouse <dwmw@amazon.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Leonard Foerster <foersleo@amazon.de>
Cc: Marco Elver <elver@google.com>
Cc: Markus Boehme <markubo@amazon.de>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/damon/Kconfig

@@ -54,7 +54,7 @@ config DAMON_VADDR_KUNIT_TEST
 
 config DAMON_DBGFS
 	bool "DAMON debugfs interface"
-	depends on DAMON_VADDR && DEBUG_FS
+	depends on DAMON_VADDR && DAMON_PADDR && DEBUG_FS
 	help
 	  This builds the debugfs interface for DAMON.  The user space admins
 	  can use the interface for arbitrary data access monitoring.

mm/damon/dbgfs.c

@@ -339,6 +339,7 @@ static ssize_t dbgfs_target_ids_write(struct file *file,
 		const char __user *buf, size_t count, loff_t *ppos)
 {
 	struct damon_ctx *ctx = file->private_data;
+	bool id_is_pid = true;
 	char *kbuf, *nrs;
 	unsigned long *targets;
 	ssize_t nr_targets;
@@ -351,6 +352,11 @@ static ssize_t dbgfs_target_ids_write(struct file *file,
 		return PTR_ERR(kbuf);
 
 	nrs = kbuf;
+	if (!strncmp(kbuf, "paddr\n", count)) {
+		id_is_pid = false;
+		/* target id is meaningless here, but we set it just for fun */
+		scnprintf(kbuf, count, "42    ");
+	}
 
 	targets = str_to_target_ids(nrs, ret, &nr_targets);
 	if (!targets) {
@@ -358,7 +364,7 @@ static ssize_t dbgfs_target_ids_write(struct file *file,
 		goto out;
 	}
 
-	if (targetid_is_pid(ctx)) {
+	if (id_is_pid) {
 		for (i = 0; i < nr_targets; i++) {
 			targets[i] = (unsigned long)find_get_pid(
 					(int)targets[i]);
@@ -372,15 +378,24 @@ static ssize_t dbgfs_target_ids_write(struct file *file,
 
 	mutex_lock(&ctx->kdamond_lock);
 	if (ctx->kdamond) {
-		if (targetid_is_pid(ctx))
+		if (id_is_pid)
 			dbgfs_put_pids(targets, nr_targets);
 		ret = -EBUSY;
 		goto unlock_out;
 	}
 
+	/* remove targets with previously-set primitive */
+	damon_set_targets(ctx, NULL, 0);
+
+	/* Configure the context for the address space type */
+	if (id_is_pid)
+		damon_va_set_primitives(ctx);
+	else
+		damon_pa_set_primitives(ctx);
+
 	err = damon_set_targets(ctx, targets, nr_targets);
 	if (err) {
-		if (targetid_is_pid(ctx))
+		if (id_is_pid)
 			dbgfs_put_pids(targets, nr_targets);
 		ret = err;
 	}