x86/intel_rdt: Support restoration of subset of permissions

As the mode of a resource group changes, the operations it can support may
also change. One way in which the supported operations are managed is to
modify the permissions of the files within the resource group's resctrl
directory.

At the moment only two possible permissions are supported: the default
permissions or no permissions in support for when the operation is "locked
down". It is possible where an operation on a resource group may have more
possibilities. For example, if by default changes can be made to the
resource group by writing to a resctrl file while the current settings can
be obtained by reading from the file, then it may be possible that in
another mode it is only possible to read the current settings, and not
change them.

Make it possible to modify some of the permissions of a resctrl file in
support of a more flexible way to manage the operations on a resource
group. In this preparation work the original behavior is maintained where
all permissions are restored.

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/8773aadfade7bcb2c48a45fa294a04d2c03bb0a1.1530421961.git.reinette.chatre@intel.com

arch/x86/kernel/cpu/intel_rdt.h

@@ -512,7 +512,8 @@ 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);
+int rdtgroup_kn_mode_restore(struct rdtgroup *r, const char *name,
+			     umode_t mask);
 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,

arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c

@@ -590,11 +590,11 @@ static int rdtgroup_locksetup_user_restrict(struct rdtgroup *rdtgrp)
 	goto out;
 
 err_cpus_list:
-	rdtgroup_kn_mode_restore(rdtgrp, "cpus_list");
+	rdtgroup_kn_mode_restore(rdtgrp, "cpus_list", 0777);
 err_cpus:
-	rdtgroup_kn_mode_restore(rdtgrp, "cpus");
+	rdtgroup_kn_mode_restore(rdtgrp, "cpus", 0777);
 err_tasks:
-	rdtgroup_kn_mode_restore(rdtgrp, "tasks");
+	rdtgroup_kn_mode_restore(rdtgrp, "tasks", 0777);
 out:
 	return ret;
 }
@@ -615,20 +615,20 @@ static int rdtgroup_locksetup_user_restore(struct rdtgroup *rdtgrp)
 {
 	int ret;
 
-	ret = rdtgroup_kn_mode_restore(rdtgrp, "tasks");
+	ret = rdtgroup_kn_mode_restore(rdtgrp, "tasks", 0777);
 	if (ret)
 		return ret;
 
-	ret = rdtgroup_kn_mode_restore(rdtgrp, "cpus");
+	ret = rdtgroup_kn_mode_restore(rdtgrp, "cpus", 0777);
 	if (ret)
 		goto err_tasks;
 
-	ret = rdtgroup_kn_mode_restore(rdtgrp, "cpus_list");
+	ret = rdtgroup_kn_mode_restore(rdtgrp, "cpus_list", 0777);
 	if (ret)
 		goto err_cpus;
 
 	if (rdt_mon_capable) {
-		ret = rdtgroup_kn_mode_restore(rdtgrp, "mon_groups");
+		ret = rdtgroup_kn_mode_restore(rdtgrp, "mon_groups", 0777);
 		if (ret)
 			goto err_cpus_list;
 	}

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c

@@ -1405,13 +1405,15 @@ int rdtgroup_kn_mode_restrict(struct rdtgroup *r, const char *name)
  * rdtgroup_kn_mode_restore - Restore user access to named resctrl file
  * @r: The resource group with which the file is associated.
  * @name: Name of the file
+ * @mask: Mask of permissions that should be restored
  *
  * Restore the permissions of the named file. If @name is a directory the
  * permissions of its parent will be used.
  *
  * Return: 0 on success, <0 on failure.
  */
-int rdtgroup_kn_mode_restore(struct rdtgroup *r, const char *name)
+int rdtgroup_kn_mode_restore(struct rdtgroup *r, const char *name,
+			     umode_t mask)
 {
 	struct iattr iattr = {.ia_valid = ATTR_MODE,};
 	struct kernfs_node *kn, *parent;
@@ -1423,7 +1425,7 @@ int rdtgroup_kn_mode_restore(struct rdtgroup *r, const char *name)
 
 	for (rft = rfts; rft < rfts + len; rft++) {
 		if (!strcmp(rft->name, name))
-			iattr.ia_mode = rft->mode;
+			iattr.ia_mode = rft->mode & mask;
 	}
 
 	kn = kernfs_find_and_get_ns(r->kn, name, NULL);