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Subject[RFC PATCH V2 06/22] x86/intel_rdt: Create pseudo-locked regions
Date
System administrator creates/removes pseudo-locked regions by
creating/removing directories in the pseudo-lock subdirectory of the
resctrl filesystem. Here we add directory creation and removal support.

A "pseudo-lock region" is introduced, which represents an
instance of a pseudo-locked cache region. During mkdir a new region is
created but since we do not know which cache it belongs to at that time
we maintain a global pointer to it from where it will be moved to the cache
(rdt_domain) it belongs to after initialization. This implies that
we only support one uninitialized pseudo-locked region at a time.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
arch/x86/kernel/cpu/intel_rdt.h | 3 +
arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c | 220 +++++++++++++++++++++++++++-
2 files changed, 222 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt.h b/arch/x86/kernel/cpu/intel_rdt.h
index 8f5ded384e19..55f085985072 100644
--- a/arch/x86/kernel/cpu/intel_rdt.h
+++ b/arch/x86/kernel/cpu/intel_rdt.h
@@ -352,6 +352,7 @@ extern struct mutex rdtgroup_mutex;
extern struct rdt_resource rdt_resources_all[];
extern struct rdtgroup rdtgroup_default;
DECLARE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
+extern struct kernfs_node *pseudo_lock_kn;

int __init rdtgroup_init(void);

@@ -457,5 +458,7 @@ bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d);
void __check_limbo(struct rdt_domain *d, bool force_free);
int rdt_pseudo_lock_fs_init(struct kernfs_node *root);
void rdt_pseudo_lock_fs_remove(void);
+int rdt_pseudo_lock_mkdir(const char *name, umode_t mode);
+int rdt_pseudo_lock_rmdir(struct kernfs_node *kn);

#endif /* _ASM_X86_INTEL_RDT_H */
diff --git a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
index a787a103c432..7a22e367b82f 100644
--- a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
+++ b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
@@ -20,11 +20,142 @@
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernfs.h>
+#include <linux/kref.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
+#include <linux/slab.h>
#include "intel_rdt.h"

-static struct kernfs_node *pseudo_lock_kn;
+struct kernfs_node *pseudo_lock_kn;
+
+/*
+ * Protect the pseudo_lock_region access. Since we will link to
+ * pseudo_lock_region from rdt domains rdtgroup_mutex should be obtained
+ * first if needed.
+ */
+static DEFINE_MUTEX(rdt_pseudo_lock_mutex);
+
+/**
+ * struct pseudo_lock_region - pseudo-lock region information
+ * @kn: kernfs node representing this region in the resctrl
+ * filesystem
+ * @cbm: bitmask of the pseudo-locked region
+ * @cpu: core associated with the cache on which the setup code
+ * will be run
+ * @minor: minor number of character device associated with this
+ * region
+ * @locked: state indicating if this region has been locked or not
+ * @refcount: how many are waiting to access this pseudo-lock
+ * region via kernfs
+ * @deleted: user requested removal of region via rmdir on kernfs
+ */
+struct pseudo_lock_region {
+ struct kernfs_node *kn;
+ u32 cbm;
+ int cpu;
+ unsigned int minor;
+ bool locked;
+ struct kref refcount;
+ bool deleted;
+};
+
+/*
+ * Only one uninitialized pseudo-locked region can exist at a time. An
+ * uninitialized pseudo-locked region is created when the user creates a
+ * new directory within the pseudo_lock subdirectory of the resctrl
+ * filsystem. The user will initialize the pseudo-locked region by writing
+ * to its schemata file at which point this structure will be moved to the
+ * cache domain it belongs to.
+ */
+static struct pseudo_lock_region *new_plr;
+
+static void __pseudo_lock_region_release(struct pseudo_lock_region *plr)
+{
+ bool is_new_plr = (plr == new_plr);
+
+ WARN_ON(!plr->deleted);
+ if (!plr->deleted)
+ return;
+
+ kfree(plr);
+ if (is_new_plr)
+ new_plr = NULL;
+}
+
+static void pseudo_lock_region_release(struct kref *ref)
+{
+ struct pseudo_lock_region *plr = container_of(ref,
+ struct pseudo_lock_region,
+ refcount);
+
+ mutex_lock(&rdt_pseudo_lock_mutex);
+ __pseudo_lock_region_release(plr);
+ mutex_unlock(&rdt_pseudo_lock_mutex);
+}
+
+/**
+ * pseudo_lock_region_kn_lock - Obtain lock to pseudo-lock region kernfs node
+ *
+ * This is called from the kernfs related functions which are called with
+ * an active reference to the kernfs_node that contains a valid pointer to
+ * the pseudo-lock region it represents. We can thus safely take an active
+ * reference to the pseudo-lock region before dropping the reference to the
+ * kernfs_node.
+ *
+ * We need to handle the scenarios where the kernfs directory representing
+ * this pseudo-lock region can be removed while an application still has an
+ * open handle to one of the directory's files and operations on this
+ * handle are attempted.
+ * To support this we allow a file operation to drop its reference to the
+ * kernfs_node so that the removal can proceed, while using the mutex to
+ * ensure these operations on the pseudo-lock region are serialized. At the
+ * time an operation does obtain access to the region it may thus have been
+ * deleted.
+ */
+static struct pseudo_lock_region *pseudo_lock_region_kn_lock(
+ struct kernfs_node *kn)
+{
+ struct pseudo_lock_region *plr = (kernfs_type(kn) == KERNFS_DIR) ?
+ kn->priv : kn->parent->priv;
+
+ WARN_ON(!plr);
+ if (!plr)
+ return NULL;
+
+ kref_get(&plr->refcount);
+ kernfs_break_active_protection(kn);
+
+ mutex_lock(&rdtgroup_mutex);
+ mutex_lock(&rdt_pseudo_lock_mutex);
+
+ if (plr->deleted)
+ return NULL;
+
+ return plr;
+}
+
+/**
+ * pseudo_lock_region_kn_unlock - Release lock to pseudo-lock region kernfs node
+ *
+ * The pseudo-lock region's kernfs_node did not have protection against
+ * removal while the lock was held. Here we do actual cleanup if the region
+ * was removed while the lock was held.
+ */
+static void pseudo_lock_region_kn_unlock(struct kernfs_node *kn)
+{
+ struct pseudo_lock_region *plr = (kernfs_type(kn) == KERNFS_DIR) ?
+ kn->priv : kn->parent->priv;
+
+ WARN_ON(!plr);
+ if (!plr)
+ return;
+
+ mutex_unlock(&rdt_pseudo_lock_mutex);
+ mutex_unlock(&rdtgroup_mutex);
+
+ kernfs_unbreak_active_protection(kn);
+ kref_put(&plr->refcount, pseudo_lock_region_release);
+}

/**
* pseudo_lock_avail_get - return bitmask of cache available for locking
@@ -96,6 +227,87 @@ static struct kernfs_ops pseudo_lock_avail_ops = {
.seq_show = pseudo_lock_avail_show,
};

+int rdt_pseudo_lock_mkdir(const char *name, umode_t mode)
+{
+ struct pseudo_lock_region *plr;
+ struct kernfs_node *kn;
+ int ret = 0;
+
+ mutex_lock(&rdtgroup_mutex);
+ mutex_lock(&rdt_pseudo_lock_mutex);
+
+ if (new_plr) {
+ ret = -ENOSPC;
+ goto out;
+ }
+
+ plr = kzalloc(sizeof(*plr), GFP_KERNEL);
+ if (!plr) {
+ ret = -ENOSPC;
+ goto out;
+ }
+
+ kn = kernfs_create_dir(pseudo_lock_kn, name, mode, plr);
+ if (IS_ERR(kn)) {
+ ret = PTR_ERR(kn);
+ goto out_free;
+ }
+
+ plr->kn = kn;
+ ret = rdtgroup_kn_set_ugid(kn);
+ if (ret)
+ goto out_remove;
+
+ kref_init(&plr->refcount);
+ kernfs_activate(kn);
+ new_plr = plr;
+ ret = 0;
+ goto out;
+
+out_remove:
+ kernfs_remove(kn);
+out_free:
+ kfree(plr);
+out:
+ mutex_unlock(&rdt_pseudo_lock_mutex);
+ mutex_unlock(&rdtgroup_mutex);
+ return ret;
+}
+
+/*
+ * rdt_pseudo_lock_rmdir - Remove pseudo-lock region
+ *
+ * LOCKING:
+ * Since the pseudo-locked region can be associated with a RDT domain at
+ * removal we take both rdtgroup_mutex and rdt_pseudo_lock_mutex to protect
+ * the rdt_domain access as well as the pseudo_lock_region access.
+ */
+int rdt_pseudo_lock_rmdir(struct kernfs_node *kn)
+{
+ struct kernfs_node *parent_kn = kn->parent;
+ struct pseudo_lock_region *plr;
+ int ret = 0;
+
+ plr = pseudo_lock_region_kn_lock(kn);
+ if (!plr) {
+ ret = -EPERM;
+ goto out;
+ }
+
+ if (parent_kn != pseudo_lock_kn) {
+ ret = -ENOENT;
+ goto out;
+ }
+
+ kernfs_remove(kn);
+ plr->deleted = true;
+ kref_put(&plr->refcount, pseudo_lock_region_release);
+
+out:
+ pseudo_lock_region_kn_unlock(kn);
+ return ret;
+}
+
/**
* rdt_pseudo_lock_fs_init - Create and initialize pseudo-locking files
* @root: location in kernfs where directory and files should be created
@@ -159,7 +371,13 @@ int rdt_pseudo_lock_fs_init(struct kernfs_node *root)
void rdt_pseudo_lock_fs_remove(void)
{
lockdep_assert_held(&rdtgroup_mutex);
+ mutex_lock(&rdt_pseudo_lock_mutex);

+ if (new_plr) {
+ new_plr->deleted = true;
+ __pseudo_lock_region_release(new_plr);
+ }
kernfs_remove(pseudo_lock_kn);
pseudo_lock_kn = NULL;
+ mutex_unlock(&rdt_pseudo_lock_mutex);
}
--
2.13.6
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