resctrl2: Add "write()" operation to tasks file

Writing a task id to the "tasks" file in a resctrl group assigns
that task to that group.

Signed-off-by: Tony Luck <tony.luck@intel.com>

4 files changed, 114 insertions, 0 deletions

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 1fc8dea4f3d090..cc18045027b3d1 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -116,6 +116,13 @@ static inline bool arch_is_resctrl_id_match(struct task_struct *t, struct resctr
 	return is_closid_match(t, rg);
 }
 
+static inline bool arch_set_task_ids(struct task_struct *t, struct resctrl_group *rg)
+{
+	WRITE_ONCE(t->resctrl_ids, rg->resctrl_ids);
+
+	return true;
+}
+
 #else
 
 static inline void resctrl_sched_in(struct task_struct *tsk) {}
diff --git a/fs/resctrl2/internal.h b/fs/resctrl2/internal.h
index a0a92b0e78643a..55e1c53768203b 100644
--- a/fs/resctrl2/internal.h
+++ b/fs/resctrl2/internal.h
@@ -52,6 +52,8 @@ struct info_file_info {
 struct core_file_info {
 	struct resctrl_group	*rg;
 	int			(*show)(struct seq_file *sf, struct resctrl_group *rg);
+	ssize_t			(*write)(char *buf, size_t nbytes, struct resctrl_group *rg,
+					 struct kernfs_open_file *of);
 };
 
 #define RESCTRL_GROUP		5
diff --git a/fs/resctrl2/kernfs.c b/fs/resctrl2/kernfs.c
index 69ba3479dccdaa..aaf4d271f4bf6d 100644
--- a/fs/resctrl2/kernfs.c
+++ b/fs/resctrl2/kernfs.c
@@ -38,9 +38,40 @@ out:
 	return ret;
 }
 
+static ssize_t resctrl_file_write(struct kernfs_open_file *of, char *buf,
+				  size_t nbytes, loff_t off)
+{
+	struct resctrl_node_info *rni;
+	struct core_file_info *cfi;
+	int ret = -EOPNOTSUPP;
+
+	rni = resctrl_kn_lock_live(of->kn);
+
+	if (!rni) {
+		ret = -ENOENT;
+		goto out;
+	}
+
+	switch (rni->type) {
+	case RESCTRL_COREFILE:
+		cfi = (struct core_file_info *)&rni->priv;
+		if (cfi->write)
+			ret = cfi->write(buf, nbytes, cfi->rg, of);
+		break;
+	default:
+		ret = -EOPNOTSUPP;
+		break;
+	}
+out:
+	resctrl_kn_unlock(of->kn);
+
+	return ret ?: nbytes;
+}
+
 struct kernfs_ops resctrl_file_ops = {
 	.atomic_write_len	= PAGE_SIZE,
 	.seq_show		= resctrl_file_show,
+	.write			= resctrl_file_write,
 };
 
 /* Set uid and gid of dirs and files to that of the creator */
diff --git a/fs/resctrl2/tasks.c b/fs/resctrl2/tasks.c
index f7765cbff84836..b3817a9b7e1b75 100644
--- a/fs/resctrl2/tasks.c
+++ b/fs/resctrl2/tasks.c
@@ -26,6 +26,79 @@ static int tasks_seq_show(struct seq_file *m, struct resctrl_group *rg)
 	return 0;
 }
 
+static int __resctrl_move_task(struct task_struct *tsk,
+			       struct resctrl_group *rg)
+{
+	/* If the task is already in group, no need to move the task. */
+	if (tsk->resctrl_ids == rg->resctrl_ids)
+		return 0;
+
+	/* Change ID in task structure first */
+	if (!arch_set_task_ids(tsk, rg))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int resctrl_task_write_permission(struct task_struct *task,
+					 struct kernfs_open_file *of)
+{
+	const struct cred *tcred = get_task_cred(task);
+	const struct cred *cred = current_cred();
+	int ret = 0;
+
+	/*
+	 * Even if we're attaching all tasks in the thread group, we only
+	 * need to check permissions on one of them.
+	 */
+	if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) &&
+	    !uid_eq(cred->euid, tcred->uid) &&
+	    !uid_eq(cred->euid, tcred->suid)) {
+		ret = -EPERM;
+	}
+
+	put_cred(tcred);
+	return ret;
+}
+
+static int resctrl_move_task(pid_t pid, struct resctrl_group *rg, struct kernfs_open_file *of)
+{
+	struct task_struct *tsk;
+	int ret;
+
+	rcu_read_lock();
+	if (pid) {
+		tsk = find_task_by_vpid(pid);
+		if (!tsk) {
+			rcu_read_unlock();
+			return -ESRCH;
+		}
+	} else {
+		tsk = current;
+	}
+
+	get_task_struct(tsk);
+	rcu_read_unlock();
+
+	ret = resctrl_task_write_permission(tsk, of);
+	if (!ret)
+		ret = __resctrl_move_task(tsk, rg);
+
+	put_task_struct(tsk);
+	return ret;
+}
+
+static ssize_t tasks_write(char *buf, size_t nbytes, struct resctrl_group *rg,
+			   struct kernfs_open_file *of)
+{
+	pid_t pid;
+
+	if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
+		return -EINVAL;
+
+	return resctrl_move_task(pid, rg, of);
+}
+
 bool resctrl_add_task_file(struct kernfs_node *parent_kn)
 {
 	struct resctrl_node_info *rni, *prni;
@@ -38,6 +111,7 @@ bool resctrl_add_task_file(struct kernfs_node *parent_kn)
 	cfi = (struct core_file_info *)&rni->priv;
 	cfi->rg = (struct resctrl_group *)&prni->priv;
 	cfi->show = tasks_seq_show;
+	cfi->write = tasks_write;
 
 	return true;
 }