linux-kernel - [patch 08/11] entry: Distinguish between syscall and interrupt exit

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Message-ID: <20250813162824.292368751@linutronix.de>
Date: Wed, 13 Aug 2025 18:29:31 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Michael Jeanson <mjeanson@...icios.com>,
 Peter Zijlstra <peterz@...radead.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 "Paul E. McKenney" <paulmck@...nel.org>,
 Boqun Feng <boqun.feng@...il.com>,
 Wei Liu <wei.liu@...nel.org>,
 Jens Axboe <axboe@...nel.dk>
Subject: [patch 08/11] entry: Distinguish between syscall and interrupt exit

The upcoming time slice extension mechanism needs to know whether
enter_from_user_mode() is invoked from a syscall or from an interrupt
because time slice extensions are only granted on exit to user more from an
interrupt.

Add a function argument and provide wrappers so the call sites don't end up
with incomprehensible true/false arguments.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
---
 include/linux/entry-common.h     |    2 +-
 include/linux/irq-entry-common.h |   22 +++++++++++++++-------
 kernel/entry/common.c            |    7 ++++---
 3 files changed, 20 insertions(+), 11 deletions(-)

--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -172,7 +172,7 @@ static __always_inline void syscall_exit
 	if (unlikely(work & SYSCALL_WORK_EXIT))
 		syscall_exit_work(regs, work);
 	local_irq_disable_exit_to_user();
-	exit_to_user_mode_prepare(regs);
+	syscall_exit_to_user_mode_prepare(regs);
 }
 
 /**
--- a/include/linux/irq-entry-common.h
+++ b/include/linux/irq-entry-common.h
@@ -197,15 +197,13 @@ static __always_inline void arch_exit_to
  */
 void arch_do_signal_or_restart(struct pt_regs *regs);
 
-/**
- * exit_to_user_mode_loop - do any pending work before leaving to user space
- */
-unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
-				     unsigned long ti_work);
+/* Handle pending TIF work */
+unsigned long exit_to_user_mode_loop(struct pt_regs *regs, unsigned long ti_work, bool from_irq);
 
 /**
  * exit_to_user_mode_prepare - call exit_to_user_mode_loop() if required
  * @regs:	Pointer to pt_regs on entry stack
+ * @from_irq:	Exiting to user space from an interrupt
  *
  * 1) check that interrupts are disabled
  * 2) call tick_nohz_user_enter_prepare()
@@ -213,7 +211,7 @@ unsigned long exit_to_user_mode_loop(str
  *    EXIT_TO_USER_MODE_WORK are set
  * 4) check that interrupts are still disabled
  */
-static __always_inline void exit_to_user_mode_prepare(struct pt_regs *regs)
+static __always_inline void exit_to_user_mode_prepare(struct pt_regs *regs, bool from_irq)
 {
 	unsigned long ti_work;
 
@@ -224,7 +222,7 @@ static __always_inline void exit_to_user
 
 	ti_work = read_thread_flags();
 	if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
-		ti_work = exit_to_user_mode_loop(regs, ti_work);
+		ti_work = exit_to_user_mode_loop(regs, ti_work, from_irq);
 
 	arch_exit_to_user_mode_prepare(regs, ti_work);
 
@@ -236,6 +234,16 @@ static __always_inline void exit_to_user
 	lockdep_sys_exit();
 }
 
+static __always_inline void syscall_exit_to_user_mode_prepare(struct pt_regs *regs)
+{
+	exit_to_user_mode_prepare(regs, false);
+}
+
+static __always_inline void irqentry_exit_to_user_mode_prepare(struct pt_regs *regs)
+{
+	exit_to_user_mode_prepare(regs, true);
+}
+
 /**
  * exit_to_user_mode - Fixup state when exiting to user mode
  *
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -15,9 +15,10 @@ void __weak arch_do_signal_or_restart(st
  * exit_to_user_mode_loop - do any pending work before leaving to user space
  * @regs:	Pointer to pt_regs on entry stack
  * @ti_work:	TIF work flags as read by the caller
+ * @from_irq:	Exiting to user space from an interrupt
  */
-__always_inline unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
-						     unsigned long ti_work)
+__always_inline unsigned long exit_to_user_mode_loop(struct pt_regs *regs, unsigned long ti_work,
+						     bool from_irq)
 {
 	/*
 	 * Before returning to user space ensure that all pending work
@@ -70,7 +71,7 @@ noinstr void irqentry_enter_from_user_mo
 noinstr void irqentry_exit_to_user_mode(struct pt_regs *regs)
 {
 	instrumentation_begin();
-	exit_to_user_mode_prepare(regs);
+	irqentry_exit_to_user_mode_prepare(regs);
 	instrumentation_end();
 	exit_to_user_mode();
 }