irq_pipeline: Clean up stage_info field and users

This field represents mutually exclusive states, namely

- IRQENTRY_INBAND_UNSTALLED
- IRQENTRY_INBAND_STALLED
- IRQENTRY_OOB

Encodes them as enum and test against them, rather than against state
bits that suggest they could be combined.

Also flip the inverted naming of INBAND_STALLED vs. INBAND_UNSTALLED:
Only when we entered under INBAND_UNSTALLED, certain actions need to be
taken on exit.

Finally, document the stage_info field of irqentry_state.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

arch/x86/kernel/irq_pipeline.c

@@ -64,7 +64,7 @@ static irqentry_state_t pipeline_enter_rcu(void)
 {
 	irqentry_state_t state = {
 		.exit_rcu = false,
-		.stage_info = 0,
+		.stage_info = IRQENTRY_INBAND_UNSTALLED,
 	};
 
 	if (!IS_ENABLED(CONFIG_TINY_RCU) && is_idle_task(current)) {
@@ -202,6 +202,7 @@ static void do_sysvec_inband(struct irq_desc *desc, struct pt_regs *regs)
 
 static void do_irq_inband(struct pt_regs *regs, u32 irq)
 {
+
 	struct irq_desc *desc = irq_to_desc(irq);
 
 	desc->handle_irq(desc);

arch/x86/mm/fault.c

@@ -813,7 +813,7 @@ static inline void cond_reenable_irqs_kernel(irqentry_state_t state,
 					struct pt_regs *regs)
 {
 	if (regs->flags & X86_EFLAGS_IF) {
-		if (state.stage_info & IRQENTRY_INBAND_STALLED)
+		if (state.stage_info == IRQENTRY_INBAND_UNSTALLED)
 			unstall_inband_nocheck();
 		hard_local_irq_enable();
 	}

include/linux/entry-common.h

@@ -399,6 +399,12 @@ void irqentry_enter_from_user_mode(struct pt_regs *regs);
  */
 void irqentry_exit_to_user_mode(struct pt_regs *regs);
 
+enum irqentry_info {
+	IRQENTRY_INBAND_UNSTALLED = 0,
+	IRQENTRY_INBAND_STALLED,
+	IRQENTRY_OOB,
+};
+
 #ifndef irqentry_state
 /**
  * struct irqentry_state - Opaque object for exception state storage
@@ -406,6 +412,7 @@ void irqentry_exit_to_user_mode(struct pt_regs *regs);
  *            exit path has to invoke rcu_irq_exit().
  * @lockdep: Used exclusively in the irqentry_nmi_*() calls; ensures that
  *           lockdep state is restored correctly on exit from nmi.
+ * @stage_info: Information about pipeline state and current stage on IRQ entry.
  *
  * This opaque object is filled in by the irqentry_*_enter() functions and
  * must be passed back into the corresponding irqentry_*_exit() functions
@@ -421,9 +428,7 @@ typedef struct irqentry_state {
 		bool	lockdep;
 	};
 #ifdef CONFIG_IRQ_PIPELINE
-#define IRQENTRY_INBAND_STALLED	BIT(0)
-#define IRQENTRY_OOB_ENTRY	BIT(1)
-	int	stage_info;
+	enum irqentry_info stage_info;
 #endif
 } irqentry_state_t;
 #endif

kernel/entry/common.c

@@ -404,13 +404,13 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
 	irqentry_state_t ret = {
 		.exit_rcu = false,
 #ifdef CONFIG_IRQ_PIPELINE
-		.stage_info = 0,
+		.stage_info = IRQENTRY_INBAND_STALLED,
 #endif
 	};
 
 #ifdef CONFIG_IRQ_PIPELINE
 	if (running_oob()) {
-		ret.stage_info = IRQENTRY_OOB_ENTRY;
+		ret.stage_info = IRQENTRY_OOB;
 		return ret;
 	}
 #endif
@@ -419,7 +419,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
 #ifdef CONFIG_IRQ_PIPELINE
 		WARN_ON_ONCE(irq_pipeline_debug() && irqs_disabled());
 		stall_inband_nocheck();
-		ret.stage_info = IRQENTRY_INBAND_STALLED;
+		ret.stage_info = IRQENTRY_INBAND_UNSTALLED;
 #endif
 		irqentry_enter_from_user_mode(regs);
 		return ret;
@@ -432,7 +432,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
 	 * irqs are off on entry, we have to stall the in-band stage.
 	 */
 	if (!test_and_stall_inband_nocheck())
-		ret.stage_info = IRQENTRY_INBAND_STALLED;
+		ret.stage_info = IRQENTRY_INBAND_UNSTALLED;
 #endif
 
 	/*
@@ -510,7 +510,7 @@ static inline
 bool irqexit_may_preempt_schedule(irqentry_state_t state,
 				struct pt_regs *regs)
 {
-	return !!(state.stage_info & IRQENTRY_INBAND_STALLED);
+	return state.stage_info == IRQENTRY_INBAND_UNSTALLED;
 }
 
 #else
@@ -579,7 +579,7 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
 	 * irqentry_enter() raised it in order to mirror the hardware
 	 * state.
 	 */
-	if (state.stage_info & IRQENTRY_INBAND_STALLED)
+	if (state.stage_info == IRQENTRY_INBAND_UNSTALLED)
 		unstall_inband();
 #endif
 	return;