[PATCH v6 05/10] x86/intel_rdt: Add mkdir to resctrl file system

[Fenghua Yu]

From: Fenghua Yu <fenghua.yu@xxxxxxxxx>

Resource control groups are represented as directories in the resctrl
file system. The root directory describes the default resources available
to tasks that have not been assigned specific resources. Other directories
can be created at the root level to make new resource groups. It is not
permitted to make directories within other directories.

Hardware uses a CLOSID (Class of service ID) to determine which resource
limits are currently in effect. The exact number available is enumerated
by CPUID leaf 0x10, but on current implementations it is a small number.
We implement a simple bitmask allocator for CLOSIDs.

Each resource control group uses one CLOSID, which limits the total number
of directories that can be created.

Resource groups can be removed using rmdir.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
 arch/x86/include/asm/intel_rdt.h         |   9 ++
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 231 +++++++++++++++++++++++++++++++
 2 files changed, 240 insertions(+)

diff --git a/arch/x86/include/asm/intel_rdt.h b/arch/x86/include/asm/intel_rdt.h
index 39ed561..a6c7d94 100644
--- a/arch/x86/include/asm/intel_rdt.h
+++ b/arch/x86/include/asm/intel_rdt.h
@@ -12,13 +12,20 @@
  * @kn:				kernfs node
  * @rdtgroup_list:		linked list for all rdtgroups
  * @closid:			closid for this rdtgroup
+ * @flags:			status bits
+ * @waitcount:			how many cpus expect to find this
  */
 struct rdtgroup {
 	struct kernfs_node	*kn;
 	struct list_head	rdtgroup_list;
 	int			closid;
+	int			flags;
+	atomic_t		waitcount;
 };
 
+/* rdtgroup.flags */
+#define	RDT_DELETED		1
+
 /* List of all resource groups */
 extern struct list_head rdt_all_groups;
 
@@ -154,4 +161,6 @@ union cpuid_0x10_1_edx {
 };
 
 void rdt_cbm_update(void *arg);
+struct rdtgroup *rdtgroup_kn_lock_live(struct kernfs_node *kn);
+void rdtgroup_kn_unlock(struct kernfs_node *kn);
 #endif /* _ASM_X86_INTEL_RDT_H */
diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index 58aa8f7..6ff35786 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -26,10 +26,12 @@
 #include <linux/seq_file.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
+#include <linux/cpu.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;
@@ -39,6 +41,55 @@ 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)
 {
@@ -271,6 +322,54 @@ static int parse_rdtgroupfs_options(char *data)
 	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)
+		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);
+
+	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);
+
+	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)
@@ -302,6 +401,8 @@ static struct dentry *rdt_mount(struct file_system_type *fs_type,
 		}
 	}
 
+	closid_init();
+
 	ret = rdtgroup_create_info_dir(rdtgroup_default.kn);
 	if (ret)
 		goto out;
@@ -358,10 +459,39 @@ static int reset_all_cbms(struct rdt_resource *r)
 }
 
 /*
+ * MSR_IA32_PQR_ASSOC is scoped per logical CPU, so all updates
+ * are always in thread context.
+ */
+static void rdt_reset_pqr_assoc_closid(void *v)
+{
+	struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
+
+	state->closid = 0;
+	wrmsr(MSR_IA32_PQR_ASSOC, state->rmid, 0);
+}
+
+/*
  * Forcibly remove all of subdirectories under root.
  */
 static void rmdir_all_sub(void)
 {
+	struct rdtgroup *rdtgrp, *tmp;
+
+	get_cpu();
+	/* Reset PQR_ASSOC MSR on this cpu. */
+	rdt_reset_pqr_assoc_closid(NULL);
+	/* Reset PQR_ASSOC MSR on the rest of cpus. */
+	smp_call_function_many(cpu_online_mask, rdt_reset_pqr_assoc_closid,
+			       NULL, 1);
+	put_cpu();
+	list_for_each_entry_safe(rdtgrp, tmp, &rdt_all_groups, rdtgroup_list) {
+		/* Remove each rdtgroup other than root */
+		if (rdtgrp == &rdtgroup_default)
+			continue;
+		kernfs_remove(rdtgrp->kn);
+		list_del(&rdtgrp->rdtgroup_list);
+		kfree(rdtgrp);
+	}
 	kernfs_remove(kn_info);
 }
 
@@ -394,7 +524,108 @@ static struct file_system_type rdt_fs_type = {
 	.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;
+
+	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)
+{
+	struct rdtgroup *rdtgrp;
+	int ret = 0;
+
+	rdtgrp = rdtgroup_kn_lock_live(kn);
+	if (!rdtgrp) {
+		rdtgroup_kn_unlock(kn);
+		return -ENOENT;
+	}
+
+	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);
+
+	rdtgroup_kn_unlock(kn);
+
+	return ret;
+}
+
 static struct kernfs_syscall_ops rdtgroup_kf_syscall_ops = {
+	.mkdir	= rdtgroup_mkdir,
+	.rmdir	= rdtgroup_rmdir,
 };
 
 static int __init rdtgroup_setup_root(void)
-- 
2.5.0