mm/damon/sysfs: support fixed virtual address ranges monitoring

This commit makes DAMON sysfs interface to support the fixed virtual
address ranges monitoring.  After this commit, writing 'fvaddr' to the
'operations' DAMON sysfs file makes DAMON uses the monitoring operations
set for fixed virtual address ranges, so that users can monitor accesses
to only interested virtual address ranges.

[sj@kernel.org: fix pid leak under fvaddr ops use case]
  Link: https://lkml.kernel.org/r/20220503220531.45913-1-sj@kernel.org
Link: https://lkml.kernel.org/r/20220426231750.48822-3-sj@kernel.orgSigned-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/damon/sysfs.c

@@ -1694,7 +1694,7 @@ static struct kobj_type damon_sysfs_attrs_ktype = {
 /* This should match with enum damon_ops_id */
 static const char * const damon_sysfs_ops_strs[] = {
 	"vaddr",
-	"unsupported",	/* fvaddr is not supported by sysfs yet */
+	"fvaddr",
 	"paddr",
 };
 
@@ -1844,9 +1844,6 @@ static ssize_t operations_store(struct kobject *kobj,
 
 	for (id = 0; id < NR_DAMON_OPS; id++) {
 		if (sysfs_streq(buf, damon_sysfs_ops_strs[id])) {
-			/* fvaddr is not supported by sysfs yet */
-			if (id == DAMON_OPS_FVADDR)
-				return -EINVAL;
 			context->ops_id = id;
 			return count;
 		}
@@ -2089,7 +2086,8 @@ static void damon_sysfs_destroy_targets(struct damon_ctx *ctx)
 	struct damon_target *t, *next;
 
 	damon_for_each_target_safe(t, next, ctx) {
-		if (ctx->ops.id == DAMON_OPS_VADDR)
+		if (ctx->ops.id == DAMON_OPS_VADDR ||
+				ctx->ops.id == DAMON_OPS_FVADDR)
 			put_pid(t->pid);
 		damon_destroy_target(t);
 	}
@@ -2136,7 +2134,8 @@ static int damon_sysfs_set_targets(struct damon_ctx *ctx,
 			damon_sysfs_destroy_targets(ctx);
 			return -ENOMEM;
 		}
-		if (ctx->ops.id == DAMON_OPS_VADDR) {
+		if (ctx->ops.id == DAMON_OPS_VADDR ||
+				ctx->ops.id == DAMON_OPS_FVADDR) {
 			t->pid = find_get_pid(sys_target->pid);
 			if (!t->pid) {
 				damon_sysfs_destroy_targets(ctx);
@@ -2206,7 +2205,7 @@ static void damon_sysfs_before_terminate(struct damon_ctx *ctx)
 {
 	struct damon_target *t, *next;
 
-	if (ctx->ops.id != DAMON_OPS_VADDR)
+	if (ctx->ops.id != DAMON_OPS_VADDR && ctx->ops.id != DAMON_OPS_FVADDR)
 		return;
 
 	mutex_lock(&ctx->kdamond_lock);