Merge tag 'x86_cache_for_v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 resource control updates from Borislav Petkov:
 "Avoid IPI-ing a task in certain cases and prevent load/store tearing
  when accessing a task's resctrl fields concurrently"

* tag 'x86_cache_for_v5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/resctrl: Apply READ_ONCE/WRITE_ONCE to task_struct.{rmid,closid}
  x86/resctrl: Use task_curr() instead of task_struct->on_cpu to prevent unnecessary IPI
  x86/resctrl: Add printf attribute to log function

3 files changed, 18 insertions, 18 deletions

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 07603064df8f..d60ed0668a59 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -56,19 +56,22 @@ static void __resctrl_sched_in(void)
 	struct resctrl_pqr_state *state = this_cpu_ptr(&pqr_state);
 	u32 closid = state->default_closid;
 	u32 rmid = state->default_rmid;
+	u32 tmp;
 
 	/*
 	 * If this task has a closid/rmid assigned, use it.
 	 * Else use the closid/rmid assigned to this cpu.
 	 */
 	if (static_branch_likely(&rdt_alloc_enable_key)) {
-		if (current->closid)
-			closid = current->closid;
+		tmp = READ_ONCE(current->closid);
+		if (tmp)
+			closid = tmp;
 	}
 
 	if (static_branch_likely(&rdt_mon_enable_key)) {
-		if (current->rmid)
-			rmid = current->rmid;
+		tmp = READ_ONCE(current->rmid);
+		if (tmp)
+			rmid = tmp;
 	}
 
 	if (closid != state->cur_closid || rmid != state->cur_rmid) {
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index ee71c47844cb..c4d320d02fd5 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -572,6 +572,7 @@ union cpuid_0x10_x_edx {
 
 void rdt_last_cmd_clear(void);
 void rdt_last_cmd_puts(const char *s);
+__printf(1, 2)
 void rdt_last_cmd_printf(const char *fmt, ...);
 
 void rdt_ctrl_update(void *arg);
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 460f3e0df106..f9190adc52cb 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -563,11 +563,11 @@ static int __rdtgroup_move_task(struct task_struct *tsk,
 	 */
 
 	if (rdtgrp->type == RDTCTRL_GROUP) {
-		tsk->closid = rdtgrp->closid;
-		tsk->rmid = rdtgrp->mon.rmid;
+		WRITE_ONCE(tsk->closid, rdtgrp->closid);
+		WRITE_ONCE(tsk->rmid, rdtgrp->mon.rmid);
 	} else if (rdtgrp->type == RDTMON_GROUP) {
 		if (rdtgrp->mon.parent->closid == tsk->closid) {
-			tsk->rmid = rdtgrp->mon.rmid;
+			WRITE_ONCE(tsk->rmid, rdtgrp->mon.rmid);
 		} else {
 			rdt_last_cmd_puts("Can't move task to different control group\n");
 			return -EINVAL;
@@ -2310,22 +2310,18 @@ static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to,
 	for_each_process_thread(p, t) {
 		if (!from || is_closid_match(t, from) ||
 		    is_rmid_match(t, from)) {
-			t->closid = to->closid;
-			t->rmid = to->mon.rmid;
+			WRITE_ONCE(t->closid, to->closid);
+			WRITE_ONCE(t->rmid, to->mon.rmid);
 
-#ifdef CONFIG_SMP
 			/*
-			 * This is safe on x86 w/o barriers as the ordering
-			 * of writing to task_cpu() and t->on_cpu is
-			 * reverse to the reading here. The detection is
-			 * inaccurate as tasks might move or schedule
-			 * before the smp function call takes place. In
-			 * such a case the function call is pointless, but
+			 * If the task is on a CPU, set the CPU in the mask.
+			 * The detection is inaccurate as tasks might move or
+			 * schedule before the smp function call takes place.
+			 * In such a case the function call is pointless, but
 			 * there is no other side effect.
 			 */
-			if (mask && t->on_cpu)
+			if (IS_ENABLED(CONFIG_SMP) && mask && task_curr(t))
 				cpumask_set_cpu(task_cpu(t), mask);
-#endif
 		}
 	}
 	read_unlock(&tasklist_lock);