x86/intel_rdt: Add utility to restrict/restore access to resctrl files

When a resource group is used for Cache Pseudo-Locking then the region of
cache ends up being orphaned with no class of service referring to it. The
resctrl files intended to manage how the classes of services are utilized
thus become irrelevant.

The fact that a resctrl file is not relevant can be communicated to the
user by setting all of its permissions to zero. That is, its read, write,
and execute permissions are unset for all users.

Introduce two utilities, rdtgroup_kn_mode_restrict() and
rdtgroup_kn_mode_restore(), that can be used to restrict and restore the
permissions of a file or directory belonging to a resource group.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Cc: vikas.shivappa@linux.intel.com
Cc: gavin.hindman@intel.com
Cc: jithu.joseph@intel.com
Cc: dave.hansen@intel.com
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/7afdbf5551b2f93cd45d61fbf5e01d87331f529a.1529706536.git.reinette.chatre@intel.com

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/intel_rdt.h b/arch/x86/kernel/cpu/intel_rdt.h
index 11c76c4b9a5e..8d56776a3bd2 100644
--- a/arch/x86/kernel/cpu/intel_rdt.h
+++ b/arch/x86/kernel/cpu/intel_rdt.h
@@ -469,6 +469,8 @@ void rdt_last_cmd_printf(const char *fmt, ...);
 void rdt_ctrl_update(void *arg);
 struct rdtgroup *rdtgroup_kn_lock_live(struct kernfs_node *kn);
 void rdtgroup_kn_unlock(struct kernfs_node *kn);
+int rdtgroup_kn_mode_restrict(struct rdtgroup *r, const char *name);
+int rdtgroup_kn_mode_restore(struct rdtgroup *r, const char *name);
 struct rdt_domain *rdt_find_domain(struct rdt_resource *r, int id,
 				   struct list_head **pos);
 ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,