/*
 * User interface for Resource Alloction in Resource Director Technology(RDT)
 *
 * Copyright (C) 2016 Intel Corporation
 *
 * Author: Fenghua Yu <fenghua.yu@intel.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * More information about RDT be found in the Intel (R) x86 Architecture
 * Software Developer Manual.
 */

#define pr_fmt(fmt)     KBUILD_MODNAME ": " fmt

#include <linux/cpu.h>
#include <linux/fs.h>
#include <linux/sysfs.h>
#include <linux/kernfs.h>
#include <linux/seq_file.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/cpu.h>
#include <linux/task_work.h>

#include <uapi/linux/magic.h>

#include <asm/intel_rdt.h>
#include <asm/intel_rdt_common.h>

DEFINE_STATIC_KEY_FALSE(rdt_enable_key);
struct kernfs_root *rdt_root;
struct rdtgroup rdtgroup_default;
LIST_HEAD(rdt_all_groups);

/* Kernel fs node for "info" directory under root */
static struct kernfs_node *kn_info;

/*
 * Trivial allocator for CLOSIDs. Since h/w only supports a small number,
 * we can keep a bitmap of free CLOSIDs in a single integer.
 *
 * Using a global CLOSID across all resources has some advantages and
 * some drawbacks:
 * + We can simply set "current->closid" to assign a task to a resource
 *   group.
 * + Context switch code can avoid extra memory references deciding which
 *   CLOSID to load into the PQR_ASSOC MSR
 * - We give up some options in configuring resource groups across multi-socket
 *   systems.
 * - Our choices on how to configure each resource become progressively more
 *   limited as the number of resources grows.
 */
static int closid_free_map;

static void closid_init(void)
{
        struct rdt_resource *r;
        int rdt_min_closid = 32;

        /* Compute rdt_min_closid across all resources */
        for_each_enabled_rdt_resource(r)
                rdt_min_closid = min(rdt_min_closid, r->num_closid);

        closid_free_map = BIT_MASK(rdt_min_closid) - 1;

        /* CLOSID 0 is always reserved for the default group */
        closid_free_map &= ~1;
}

int closid_alloc(void)
{
        int closid = ffs(closid_free_map);

        if (closid == 0)
                return -ENOSPC;
        closid--;
        closid_free_map &= ~(1 << closid);

        return closid;
}

static void closid_free(int closid)
{
        closid_free_map |= 1 << closid;
}

/* set uid and gid of rdtgroup dirs and files to that of the creator */
static int rdtgroup_kn_set_ugid(struct kernfs_node *kn)
{
        struct iattr iattr = { .ia_valid = ATTR_UID | ATTR_GID,
                                .ia_uid = current_fsuid(),
                                .ia_gid = current_fsgid(), };

        if (uid_eq(iattr.ia_uid, GLOBAL_ROOT_UID) &&
            gid_eq(iattr.ia_gid, GLOBAL_ROOT_GID))
                return 0;

        return kernfs_setattr(kn, &iattr);
}

static int rdtgroup_add_file(struct kernfs_node *parent_kn, struct rftype *rft)
{
        struct kernfs_node *kn;
        int ret;

        kn = __kernfs_create_file(parent_kn, rft->name, rft->mode,
                                  0, rft->kf_ops, rft, NULL, NULL);
        if (IS_ERR(kn))
                return PTR_ERR(kn);

        ret = rdtgroup_kn_set_ugid(kn);
        if (ret) {
                kernfs_remove(kn);
                return ret;
        }

        return 0;
}

static int rdtgroup_add_files(struct kernfs_node *kn, struct rftype *rfts,
                              int len)
{
        struct rftype *rft;
        int ret;

        lockdep_assert_held(&rdtgroup_mutex);

        for (rft = rfts; rft < rfts + len; rft++) {
                ret = rdtgroup_add_file(kn, rft);
                if (ret)
                        goto error;
        }

        return 0;
error:
        pr_warn("Failed to add %s, err=%d\n", rft->name, ret);
        while (--rft >= rfts)
                kernfs_remove_by_name(kn, rft->name);
        return ret;
}

static int rdtgroup_seqfile_show(struct seq_file *m, void *arg)
{
        struct kernfs_open_file *of = m->private;
        struct rftype *rft = of->kn->priv;

        if (rft->seq_show)
                return rft->seq_show(of, m, arg);
        return 0;
}

static ssize_t rdtgroup_file_write(struct kernfs_open_file *of, char *buf,
                                   size_t nbytes, loff_t off)
{
        struct rftype *rft = of->kn->priv;

        if (rft->write)
                return rft->write(of, buf, nbytes, off);

        return -EINVAL;
}

static struct kernfs_ops rdtgroup_kf_single_ops = {
        .atomic_write_len       = PAGE_SIZE,
        .write                  = rdtgroup_file_write,
        .seq_show               = rdtgroup_seqfile_show,
};

static int rdtgroup_cpus_show(struct kernfs_open_file *of,
                              struct seq_file *s, void *v)
{
        struct rdtgroup *rdtgrp;
        int ret = 0;

        rdtgrp = rdtgroup_kn_lock_live(of->kn);

        if (rdtgrp)
                seq_printf(s, "%*pb\n", cpumask_pr_args(&rdtgrp->cpu_mask));
        else
                ret = -ENOENT;
        rdtgroup_kn_unlock(of->kn);

        return ret;
}

/*
 * This is safe against intel_rdt_sched_in() called from __switch_to()
 * because __switch_to() is executed with interrupts disabled. A local call
 * from rdt_update_closid() is proteced against __switch_to() because
 * preemption is disabled.
 */
static void rdt_update_cpu_closid(void *closid)
{
        if (closid)
                this_cpu_write(cpu_closid, *(int *)closid);
        /*
         * We cannot unconditionally write the MSR because the current
         * executing task might have its own closid selected. Just reuse
         * the context switch code.
         */
        intel_rdt_sched_in();
}

/*
 * Update the PGR_ASSOC MSR on all cpus in @cpu_mask,
 *
 * Per task closids must have been set up before calling this function.
 *
 * The per cpu closids are updated with the smp function call, when @closid
 * is not NULL. If @closid is NULL then all affected percpu closids must
 * have been set up before calling this function.
 */
static void
rdt_update_closid(const struct cpumask *cpu_mask, int *closid)
{
        int cpu = get_cpu();

        if (cpumask_test_cpu(cpu, cpu_mask))
                rdt_update_cpu_closid(closid);
        smp_call_function_many(cpu_mask, rdt_update_cpu_closid, closid, 1);
        put_cpu();
}

static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
                                   char *buf, size_t nbytes, loff_t off)
{
        cpumask_var_t tmpmask, newmask;
        struct rdtgroup *rdtgrp, *r;
        int ret;

        if (!buf)
                return -EINVAL;

        if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
                return -ENOMEM;
        if (!zalloc_cpumask_var(&newmask, GFP_KERNEL)) {
                free_cpumask_var(tmpmask);
                return -ENOMEM;
        }

        rdtgrp = rdtgroup_kn_lock_live(of->kn);
        if (!rdtgrp) {
                ret = -ENOENT;
                goto unlock;
        }

        ret = cpumask_parse(buf, newmask);
        if (ret)
                goto unlock;

        /* check that user didn't specify any offline cpus */
        cpumask_andnot(tmpmask, newmask, cpu_online_mask);
        if (cpumask_weight(tmpmask)) {
                ret = -EINVAL;
                goto unlock;
        }

        /* Check whether cpus are dropped from this group */
        cpumask_andnot(tmpmask, &rdtgrp->cpu_mask, newmask);
        if (cpumask_weight(tmpmask)) {
                /* Can't drop from default group */
                if (rdtgrp == &rdtgroup_default) {
                        ret = -EINVAL;
                        goto unlock;
                }
                /* Give any dropped cpus to rdtgroup_default */
                cpumask_or(&rdtgroup_default.cpu_mask,
                           &rdtgroup_default.cpu_mask, tmpmask);
                rdt_update_closid(tmpmask, &rdtgroup_default.closid);
        }

        /*
         * If we added cpus, remove them from previous group that owned them
         * and update per-cpu closid
         */
        cpumask_andnot(tmpmask, newmask, &rdtgrp->cpu_mask);
        if (cpumask_weight(tmpmask)) {
                list_for_each_entry(r, &rdt_all_groups, rdtgroup_list) {
                        if (r == rdtgrp)
                                continue;
                        cpumask_andnot(&r->cpu_mask, &r->cpu_mask, tmpmask);
                }
                rdt_update_closid(tmpmask, &rdtgrp->closid);
        }

        /* Done pushing/pulling - update this group with new mask */
        cpumask_copy(&rdtgrp->cpu_mask, newmask);

unlock:
        rdtgroup_kn_unlock(of->kn);
        free_cpumask_var(tmpmask);
        free_cpumask_var(newmask);

        return ret ?: nbytes;
}

struct task_move_callback {
        struct callback_head    work;
        struct rdtgroup         *rdtgrp;
};

static void move_myself(struct callback_head *head)
{
        struct task_move_callback *callback;
        struct rdtgroup *rdtgrp;

        callback = container_of(head, struct task_move_callback, work);
        rdtgrp = callback->rdtgrp;

        /*
         * If resource group was deleted before this task work callback
         * was invoked, then assign the task to root group and free the
         * resource group.
         */
        if (atomic_dec_and_test(&rdtgrp->waitcount) &&
            (rdtgrp->flags & RDT_DELETED)) {
                current->closid = 0;
                kfree(rdtgrp);
        }

        preempt_disable();
        /* update PQR_ASSOC MSR to make resource group go into effect */
        intel_rdt_sched_in();
        preempt_enable();

        kfree(callback);
}

static int __rdtgroup_move_task(struct task_struct *tsk,
                                struct rdtgroup *rdtgrp)
{
        struct task_move_callback *callback;
        int ret;

        callback = kzalloc(sizeof(*callback), GFP_KERNEL);
        if (!callback)
                return -ENOMEM;
        callback->work.func = move_myself;
        callback->rdtgrp = rdtgrp;

        /*
         * Take a refcount, so rdtgrp cannot be freed before the
         * callback has been invoked.
         */
        atomic_inc(&rdtgrp->waitcount);
        ret = task_work_add(tsk, &callback->work, true);
        if (ret) {
                /*
                 * Task is exiting. Drop the refcount and free the callback.
                 * No need to check the refcount as the group cannot be
                 * deleted before the write function unlocks rdtgroup_mutex.
                 */
                atomic_dec(&rdtgrp->waitcount);
                kfree(callback);
        } else {
                tsk->closid = rdtgrp->closid;
        }
        return ret;
}

static int rdtgroup_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 rdtgroup_move_task(pid_t pid, struct rdtgroup *rdtgrp,
                              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 = rdtgroup_task_write_permission(tsk, of);
        if (!ret)
                ret = __rdtgroup_move_task(tsk, rdtgrp);

        put_task_struct(tsk);
        return ret;
}

static ssize_t rdtgroup_tasks_write(struct kernfs_open_file *of,
                                    char *buf, size_t nbytes, loff_t off)
{
        struct rdtgroup *rdtgrp;
        int ret = 0;
        pid_t pid;

        if (kstrtoint(strstrip(buf), 0, &pid) || pid < 0)
                return -EINVAL;
        rdtgrp = rdtgroup_kn_lock_live(of->kn);

        if (rdtgrp)
                ret = rdtgroup_move_task(pid, rdtgrp, of);
        else
                ret = -ENOENT;

        rdtgroup_kn_unlock(of->kn);

        return ret ?: nbytes;
}

static void show_rdt_tasks(struct rdtgroup *r, struct seq_file *s)
{
        struct task_struct *p, *t;

        rcu_read_lock();
        for_each_process_thread(p, t) {
                if (t->closid == r->closid)
                        seq_printf(s, "%d\n", t->pid);
        }
        rcu_read_unlock();
}

static int rdtgroup_tasks_show(struct kernfs_open_file *of,
                               struct seq_file *s, void *v)
{
        struct rdtgroup *rdtgrp;
        int ret = 0;

        rdtgrp = rdtgroup_kn_lock_live(of->kn);
        if (rdtgrp)
                show_rdt_tasks(rdtgrp, s);
        else
                ret = -ENOENT;
        rdtgroup_kn_unlock(of->kn);

        return ret;
}

/* Files in each rdtgroup */
static struct rftype rdtgroup_base_files[] = {
        {
                .name           = "cpus",
                .mode           = 0644,
                .kf_ops         = &rdtgroup_kf_single_ops,
                .write          = rdtgroup_cpus_write,
                .seq_show       = rdtgroup_cpus_show,
        },
        {
                .name           = "tasks",
                .mode           = 0644,
                .kf_ops         = &rdtgroup_kf_single_ops,
                .write          = rdtgroup_tasks_write,
                .seq_show       = rdtgroup_tasks_show,
        },
        {
                .name           = "schemata",
                .mode           = 0644,
                .kf_ops         = &rdtgroup_kf_single_ops,
                .write          = rdtgroup_schemata_write,
                .seq_show       = rdtgroup_schemata_show,
        },
};

static int rdt_num_closids_show(struct kernfs_open_file *of,
                                struct seq_file *seq, void *v)
{
        struct rdt_resource *r = of->kn->parent->priv;

        seq_printf(seq, "%d\n", r->num_closid);

        return 0;
}

static int rdt_cbm_mask_show(struct kernfs_open_file *of,
                             struct seq_file *seq, void *v)
{
        struct rdt_resource *r = of->kn->parent->priv;

        seq_printf(seq, "%x\n", r->max_cbm);

        return 0;
}

static int rdt_min_cbm_bits_show(struct kernfs_open_file *of,
                             struct seq_file *seq, void *v)
{
        struct rdt_resource *r = of->kn->parent->priv;

        seq_printf(seq, "%d\n", r->min_cbm_bits);

        return 0;
}

/* rdtgroup information files for one cache resource. */
static struct rftype res_info_files[] = {
        {
                .name           = "num_closids",
                .mode           = 0444,
                .kf_ops         = &rdtgroup_kf_single_ops,
                .seq_show       = rdt_num_closids_show,
        },
        {
                .name           = "cbm_mask",
                .mode           = 0444,
                .kf_ops         = &rdtgroup_kf_single_ops,
                .seq_show       = rdt_cbm_mask_show,
        },
        {
                .name           = "min_cbm_bits",
                .mode           = 0444,
                .kf_ops         = &rdtgroup_kf_single_ops,
                .seq_show       = rdt_min_cbm_bits_show,
        },
};

static int rdtgroup_create_info_dir(struct kernfs_node *parent_kn)
{
        struct kernfs_node *kn_subdir;
        struct rdt_resource *r;
        int ret;

        /* create the directory */
        kn_info = kernfs_create_dir(parent_kn, "info", parent_kn->mode, NULL);
        if (IS_ERR(kn_info))
                return PTR_ERR(kn_info);
        kernfs_get(kn_info);

        for_each_enabled_rdt_resource(r) {
                kn_subdir = kernfs_create_dir(kn_info, r->name,
                                              kn_info->mode, r);
                if (IS_ERR(kn_subdir)) {
                        ret = PTR_ERR(kn_subdir);
                        goto out_destroy;
                }
                kernfs_get(kn_subdir);
                ret = rdtgroup_kn_set_ugid(kn_subdir);
                if (ret)
                        goto out_destroy;
                ret = rdtgroup_add_files(kn_subdir, res_info_files,
                                         ARRAY_SIZE(res_info_files));
                if (ret)
                        goto out_destroy;
                kernfs_activate(kn_subdir);
        }

        /*
         * This extra ref will be put in kernfs_remove() and guarantees
         * that @rdtgrp->kn is always accessible.
         */
        kernfs_get(kn_info);

        ret = rdtgroup_kn_set_ugid(kn_info);
        if (ret)
                goto out_destroy;

        kernfs_activate(kn_info);

        return 0;

out_destroy:
        kernfs_remove(kn_info);
        return ret;
}

static void l3_qos_cfg_update(void *arg)
{
        bool *enable = arg;

        wrmsrl(IA32_L3_QOS_CFG, *enable ? L3_QOS_CDP_ENABLE : 0ULL);
}

static int set_l3_qos_cfg(struct rdt_resource *r, bool enable)
{
        cpumask_var_t cpu_mask;
        struct rdt_domain *d;
        int cpu;

        if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL))
                return -ENOMEM;

        list_for_each_entry(d, &r->domains, list) {
                /* Pick one CPU from each domain instance to update MSR */
                cpumask_set_cpu(cpumask_any(&d->cpu_mask), cpu_mask);
        }
        cpu = get_cpu();
        /* Update QOS_CFG MSR on this cpu if it's in cpu_mask. */
        if (cpumask_test_cpu(cpu, cpu_mask))
                l3_qos_cfg_update(&enable);
        /* Update QOS_CFG MSR on all other cpus in cpu_mask. */
        smp_call_function_many(cpu_mask, l3_qos_cfg_update, &enable, 1);
        put_cpu();

        free_cpumask_var(cpu_mask);

        return 0;
}

static int cdp_enable(void)
{
        struct rdt_resource *r_l3data = &rdt_resources_all[RDT_RESOURCE_L3DATA];
        struct rdt_resource *r_l3code = &rdt_resources_all[RDT_RESOURCE_L3CODE];
        struct rdt_resource *r_l3 = &rdt_resources_all[RDT_RESOURCE_L3];
        int ret;

        if (!r_l3->capable || !r_l3data->capable || !r_l3code->capable)
                return -EINVAL;

        ret = set_l3_qos_cfg(r_l3, true);
        if (!ret) {
                r_l3->enabled = false;
                r_l3data->enabled = true;
                r_l3code->enabled = true;
        }
        return ret;
}

static void cdp_disable(void)
{
        struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3];

        r->enabled = r->capable;

        if (rdt_resources_all[RDT_RESOURCE_L3DATA].enabled) {
                rdt_resources_all[RDT_RESOURCE_L3DATA].enabled = false;
                rdt_resources_all[RDT_RESOURCE_L3CODE].enabled = false;
                set_l3_qos_cfg(r, false);
        }
}

static int parse_rdtgroupfs_options(char *data)
{
        char *token, *o = data;
        int ret = 0;

        while ((token = strsep(&o, ",")) != NULL) {
                if (!*token)
                        return -EINVAL;

                if (!strcmp(token, "cdp"))
                        ret = cdp_enable();
        }

        return ret;
}

/*
 * We don't allow rdtgroup directories to be created anywhere
 * except the root directory. Thus when looking for the rdtgroup
 * structure for a kernfs node we are either looking at a directory,
 * in which case the rdtgroup structure is pointed at by the "priv"
 * field, otherwise we have a file, and need only look to the parent
 * to find the rdtgroup.
 */
static struct rdtgroup *kernfs_to_rdtgroup(struct kernfs_node *kn)
{
        if (kernfs_type(kn) == KERNFS_DIR) {
                /*
                 * All the resource directories use "kn->priv"
                 * to point to the "struct rdtgroup" for the
                 * resource. "info" and its subdirectories don't
                 * have rdtgroup structures, so return NULL here.
                 */
                if (kn == kn_info || kn->parent == kn_info)
                        return NULL;
                else
                        return kn->priv;
        } else {
                return kn->parent->priv;
        }
}

struct rdtgroup *rdtgroup_kn_lock_live(struct kernfs_node *kn)
{
        struct rdtgroup *rdtgrp = kernfs_to_rdtgroup(kn);

        if (!rdtgrp)
                return NULL;

        atomic_inc(&rdtgrp->waitcount);
        kernfs_break_active_protection(kn);

        mutex_lock(&rdtgroup_mutex);

        /* Was this group deleted while we waited? */
        if (rdtgrp->flags & RDT_DELETED)
                return NULL;

        return rdtgrp;
}

void rdtgroup_kn_unlock(struct kernfs_node *kn)
{
        struct rdtgroup *rdtgrp = kernfs_to_rdtgroup(kn);

        if (!rdtgrp)
                return;

        mutex_unlock(&rdtgroup_mutex);

        if (atomic_dec_and_test(&rdtgrp->waitcount) &&
            (rdtgrp->flags & RDT_DELETED)) {
                kernfs_unbreak_active_protection(kn);
                kernfs_put(kn);
                kfree(rdtgrp);
        } else {
                kernfs_unbreak_active_protection(kn);
        }
}

static struct dentry *rdt_mount(struct file_system_type *fs_type,
                                int flags, const char *unused_dev_name,
                                void *data)
{
        struct dentry *dentry;
        int ret;

        mutex_lock(&rdtgroup_mutex);
        /*
         * resctrl file system can only be mounted once.
         */
        if (static_branch_unlikely(&rdt_enable_key)) {
                dentry = ERR_PTR(-EBUSY);
                goto out;
        }

        ret = parse_rdtgroupfs_options(data);
        if (ret) {
                dentry = ERR_PTR(ret);
                goto out_cdp;
        }

        closid_init();

        ret = rdtgroup_create_info_dir(rdtgroup_default.kn);
        if (ret) {
                dentry = ERR_PTR(ret);
                goto out_cdp;
        }

        dentry = kernfs_mount(fs_type, flags, rdt_root,
                              RDTGROUP_SUPER_MAGIC, NULL);
        if (IS_ERR(dentry))
                goto out_cdp;

        static_branch_enable(&rdt_enable_key);
        goto out;

out_cdp:
        cdp_disable();
out:
        mutex_unlock(&rdtgroup_mutex);

        return dentry;
}

static int reset_all_cbms(struct rdt_resource *r)
{
        struct msr_param msr_param;
        cpumask_var_t cpu_mask;
        struct rdt_domain *d;
        int i, cpu;

        if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL))
                return -ENOMEM;

        msr_param.res = r;
        msr_param.low = 0;
        msr_param.high = r->num_closid;

        /*
         * Disable resource control for this resource by setting all
         * CBMs in all domains to the maximum mask value. Pick one CPU
         * from each domain to update the MSRs below.
         */
        list_for_each_entry(d, &r->domains, list) {
                cpumask_set_cpu(cpumask_any(&d->cpu_mask), cpu_mask);

                for (i = 0; i < r->num_closid; i++)
                        d->cbm[i] = r->max_cbm;
        }
        cpu = get_cpu();
        /* Update CBM on this cpu if it's in cpu_mask. */
        if (cpumask_test_cpu(cpu, cpu_mask))
                rdt_cbm_update(&msr_param);
        /* Update CBM on all other cpus in cpu_mask. */
        smp_call_function_many(cpu_mask, rdt_cbm_update, &msr_param, 1);
        put_cpu();

        free_cpumask_var(cpu_mask);

        return 0;
}

/*
 * Move tasks from one to the other group. If @from is NULL, then all tasks
 * in the systems are moved unconditionally (used for teardown).
 *
 * If @mask is not NULL the cpus on which moved tasks are running are set
 * in that mask so the update smp function call is restricted to affected
 * cpus.
 */
static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to,
                                 struct cpumask *mask)
{
        struct task_struct *p, *t;

        read_lock(&tasklist_lock);
        for_each_process_thread(p, t) {
                if (!from || t->closid == from->closid) {
                        t->closid = to->closid;
#ifdef CONFIG_SMP
                        /*
                         * This is safe on x86 w/o barriers as the ordering
                         * of writing to task_cpu() and t->on_cpu is
                         * reverse to the reading here. The detection is
                         * inaccurate as tasks might move or schedule
                         * before the smp function call takes place. In
                         * such a case the function call is pointless, but
                         * there is no other side effect.
                         */
                        if (mask && t->on_cpu)
                                cpumask_set_cpu(task_cpu(t), mask);
#endif
                }
        }
        read_unlock(&tasklist_lock);
}

/*
 * Forcibly remove all of subdirectories under root.
 */
static void rmdir_all_sub(void)
{
        struct rdtgroup *rdtgrp, *tmp;

        /* Move all tasks to the default resource group */
        rdt_move_group_tasks(NULL, &rdtgroup_default, NULL);

        list_for_each_entry_safe(rdtgrp, tmp, &rdt_all_groups, rdtgroup_list) {
                /* Remove each rdtgroup other than root */
                if (rdtgrp == &rdtgroup_default)
                        continue;

                /*
                 * Give any CPUs back to the default group. We cannot copy
                 * cpu_online_mask because a CPU might have executed the
                 * offline callback already, but is still marked online.
                 */
                cpumask_or(&rdtgroup_default.cpu_mask,
                           &rdtgroup_default.cpu_mask, &rdtgrp->cpu_mask);

                kernfs_remove(rdtgrp->kn);
                list_del(&rdtgrp->rdtgroup_list);
                kfree(rdtgrp);
        }
        /* Notify online CPUs to update per cpu storage and PQR_ASSOC MSR */
        get_online_cpus();
        rdt_update_closid(cpu_online_mask, &rdtgroup_default.closid);
        put_online_cpus();

        kernfs_remove(kn_info);
}

static void rdt_kill_sb(struct super_block *sb)
{
        struct rdt_resource *r;

        mutex_lock(&rdtgroup_mutex);

        /*Put everything back to default values. */
        for_each_enabled_rdt_resource(r)
                reset_all_cbms(r);
        cdp_disable();
        rmdir_all_sub();
        static_branch_disable(&rdt_enable_key);
        kernfs_kill_sb(sb);
        mutex_unlock(&rdtgroup_mutex);
}

static struct file_system_type rdt_fs_type = {
        .name    = "resctrl",
        .mount   = rdt_mount,
        .kill_sb = rdt_kill_sb,
};

static int rdtgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
                          umode_t mode)
{
        struct rdtgroup *parent, *rdtgrp;
        struct kernfs_node *kn;
        int ret, closid;

        /* Only allow mkdir in the root directory */
        if (parent_kn != rdtgroup_default.kn)
                return -EPERM;

        /* Do not accept '\n' to avoid unparsable situation. */
        if (strchr(name, '\n'))
                return -EINVAL;

        parent = rdtgroup_kn_lock_live(parent_kn);
        if (!parent) {
                ret = -ENODEV;
                goto out_unlock;
        }

        ret = closid_alloc();
        if (ret < 0)
                goto out_unlock;
        closid = ret;

        /* allocate the rdtgroup. */
        rdtgrp = kzalloc(sizeof(*rdtgrp), GFP_KERNEL);
        if (!rdtgrp) {
                ret = -ENOSPC;
                goto out_closid_free;
        }
        rdtgrp->closid = closid;
        list_add(&rdtgrp->rdtgroup_list, &rdt_all_groups);

        /* kernfs creates the directory for rdtgrp */
        kn = kernfs_create_dir(parent->kn, name, mode, rdtgrp);
        if (IS_ERR(kn)) {
                ret = PTR_ERR(kn);
                goto out_cancel_ref;
        }
        rdtgrp->kn = kn;

        /*
         * kernfs_remove() will drop the reference count on "kn" which
         * will free it. But we still need it to stick around for the
         * rdtgroup_kn_unlock(kn} call below. Take one extra reference
         * here, which will be dropped inside rdtgroup_kn_unlock().
         */
        kernfs_get(kn);

        ret = rdtgroup_kn_set_ugid(kn);
        if (ret)
                goto out_destroy;

        ret = rdtgroup_add_files(kn, rdtgroup_base_files,
                                 ARRAY_SIZE(rdtgroup_base_files));
        if (ret)
                goto out_destroy;

        kernfs_activate(kn);

        ret = 0;
        goto out_unlock;

out_destroy:
        kernfs_remove(rdtgrp->kn);
out_cancel_ref:
        list_del(&rdtgrp->rdtgroup_list);
        kfree(rdtgrp);
out_closid_free:
        closid_free(closid);
out_unlock:
        rdtgroup_kn_unlock(parent_kn);
        return ret;
}

static int rdtgroup_rmdir(struct kernfs_node *kn)
{
        int ret, cpu, closid = rdtgroup_default.closid;
        struct rdtgroup *rdtgrp;
        cpumask_var_t tmpmask;

        if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
                return -ENOMEM;

        rdtgrp = rdtgroup_kn_lock_live(kn);
        if (!rdtgrp) {

                ret = -EPERM;
                goto out;
        }

        /* Give any tasks back to the default group */
        rdt_move_group_tasks(rdtgrp, &rdtgroup_default, tmpmask);

        /* Give any CPUs back to the default group */
        cpumask_or(&rdtgroup_default.cpu_mask,
                   &rdtgroup_default.cpu_mask, &rdtgrp->cpu_mask);

        /* Update per cpu closid of the moved CPUs first */
        for_each_cpu(cpu, &rdtgrp->cpu_mask)
                per_cpu(cpu_closid, cpu) = closid;
        /*
         * Update the MSR on moved CPUs and CPUs which have moved
         * task running on them.
         */
        cpumask_or(tmpmask, tmpmask, &rdtgrp->cpu_mask);
        rdt_update_closid(tmpmask, NULL);

        rdtgrp->flags = RDT_DELETED;
        closid_free(rdtgrp->closid);
        list_del(&rdtgrp->rdtgroup_list);

        /*
         * one extra hold on this, will drop when we kfree(rdtgrp)
         * in rdtgroup_kn_unlock()
         */
        kernfs_get(kn);
        kernfs_remove(rdtgrp->kn);
        ret = 0;
out:
        rdtgroup_kn_unlock(kn);
        free_cpumask_var(tmpmask);
        return ret;
}

static int rdtgroup_show_options(struct seq_file *seq, struct kernfs_root *kf)
{
        if (rdt_resources_all[RDT_RESOURCE_L3DATA].enabled)
                seq_puts(seq, ",cdp");
        return 0;
}

static struct kernfs_syscall_ops rdtgroup_kf_syscall_ops = {
        .mkdir          = rdtgroup_mkdir,
        .rmdir          = rdtgroup_rmdir,
        .show_options   = rdtgroup_show_options,
};

static int __init rdtgroup_setup_root(void)
{
        int ret;

        rdt_root = kernfs_create_root(&rdtgroup_kf_syscall_ops,
                                      KERNFS_ROOT_CREATE_DEACTIVATED,
                                      &rdtgroup_default);
        if (IS_ERR(rdt_root))
                return PTR_ERR(rdt_root);

        mutex_lock(&rdtgroup_mutex);

        rdtgroup_default.closid = 0;
        list_add(&rdtgroup_default.rdtgroup_list, &rdt_all_groups);

        ret = rdtgroup_add_files(rdt_root->kn, rdtgroup_base_files,
                                 ARRAY_SIZE(rdtgroup_base_files));
        if (ret) {
                kernfs_destroy_root(rdt_root);
                goto out;
        }

        rdtgroup_default.kn = rdt_root->kn;
        kernfs_activate(rdtgroup_default.kn);

out:
        mutex_unlock(&rdtgroup_mutex);

        return ret;
}

/*
 * rdtgroup_init - rdtgroup initialization
 *
 * Setup resctrl file system including set up root, create mount point,
 * register rdtgroup filesystem, and initialize files under root directory.
 *
 * Return: 0 on success or -errno
 */
int __init rdtgroup_init(void)
{
        int ret = 0;

        ret = rdtgroup_setup_root();
        if (ret)
                return ret;

        ret = sysfs_create_mount_point(fs_kobj, "resctrl");
        if (ret)
                goto cleanup_root;

        ret = register_filesystem(&rdt_fs_type);
        if (ret)
                goto cleanup_mountpoint;

        return 0;

cleanup_mountpoint:
        sysfs_remove_mount_point(fs_kobj, "resctrl");
cleanup_root:
        kernfs_destroy_root(rdt_root);

        return ret;
}