[PATCH v6 18/24] x86/resctrl: Make rdt_enable_key the arch's decision to switch

[James Morse <james.morse@arm.com>]

rdt_enable_key is switched when resctrl is mounted. It was also previously
used to prevent a second mount of the filesystem.

Any other architecture that wants to support resctrl has to provide
identical static keys.

Now that there are helpers for enabling and disabling the alloc/mon keys,
resctrl doesn't need to switch this extra key, it can be done by the arch
code. Use the static-key increment and decrement helpers, and change
resctrl to ensure the calls are balanced.

Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-By: Peter Newman <peternewman@google.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/include/asm/resctrl.h         |  4 ++++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 11 +++++------
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 3c9137b6ad4f..b74aa34dc9e8 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -45,21 +45,25 @@ DECLARE_STATIC_KEY_FALSE(rdt_mon_enable_key);
 static inline void resctrl_arch_enable_alloc(void)
 {
 	static_branch_enable_cpuslocked(&rdt_alloc_enable_key);
+	static_branch_inc_cpuslocked(&rdt_enable_key);
 }
 
 static inline void resctrl_arch_disable_alloc(void)
 {
 	static_branch_disable_cpuslocked(&rdt_alloc_enable_key);
+	static_branch_dec_cpuslocked(&rdt_enable_key);
 }
 
 static inline void resctrl_arch_enable_mon(void)
 {
 	static_branch_enable_cpuslocked(&rdt_mon_enable_key);
+	static_branch_inc_cpuslocked(&rdt_enable_key);
 }
 
 static inline void resctrl_arch_disable_mon(void)
 {
 	static_branch_disable_cpuslocked(&rdt_mon_enable_key);
+	static_branch_dec_cpuslocked(&rdt_enable_key);
 }
 
 /*
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 4c0e012142e2..a2391cc05f20 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -2546,10 +2546,8 @@ static int rdt_get_tree(struct fs_context *fc)
 	if (rdt_mon_capable)
 		resctrl_arch_enable_mon();
 
-	if (rdt_alloc_capable || rdt_mon_capable) {
-		static_branch_enable_cpuslocked(&rdt_enable_key);
+	if (rdt_alloc_capable || rdt_mon_capable)
 		resctrl_mounted = true;
-	}
 
 	if (is_mbm_enabled()) {
 		r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
@@ -2817,9 +2815,10 @@ static void rdt_kill_sb(struct super_block *sb)
 	rdt_pseudo_lock_release();
 	rdtgroup_default.mode = RDT_MODE_SHAREABLE;
 	schemata_list_destroy();
-	resctrl_arch_disable_alloc();
-	resctrl_arch_disable_mon();
-	static_branch_disable_cpuslocked(&rdt_enable_key);
+	if (rdt_alloc_capable)
+		resctrl_arch_disable_alloc();
+	if (rdt_mon_capable)
+		resctrl_arch_disable_mon();
 	resctrl_mounted = false;
 	kernfs_kill_sb(sb);
 	mutex_unlock(&rdtgroup_mutex);
-- 
2.39.2