linux-kernel - [PATCH v2 5/5] entry: add syscall_exit_to_user_mode

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Date:   Tue,  1 Dec 2020 15:27:55 +0100
From:   Sven Schnelle <svens@...ux.ibm.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Sven Schnelle <svens@...ux.ibm.com>
Subject: [PATCH v2 5/5] entry: add syscall_exit_to_user_mode_work()

This is the same as syscall_exit_to_user_mode() but without
calling exit_to_user_mode(). This is useful if a syscall has to be
restarted without leaving to user space.

Signed-off-by: Sven Schnelle <svens@...ux.ibm.com>
---
 include/linux/entry-common.h |  9 +++++++++
 kernel/entry/common.c        | 14 ++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index 112007525f50..bdf6b005bbfb 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -312,6 +312,15 @@ static inline void arch_syscall_exit_tracehook(struct pt_regs *regs, bool step)
  */
 void syscall_exit_to_user_mode(struct pt_regs *regs);
 
+/**
+ * syscall_exit_to_user_mode_work - Handle work before returning to user mode
+ * @regs:	Pointer to currents pt_regs
+ *
+ * Same as syscall_exit_to_user_mode() but without calling exit_to_user_mode()
+ * to perform the final transition to user mode.
+ */
+void syscall_exit_to_user_mode_work(struct pt_regs *regs);
+
 /**
  * irqentry_enter_from_user_mode - Establish state before invoking the irq handler
  * @regs:	Pointer to currents pt_regs
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index e696f6912642..c3c4ba21824a 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -246,12 +246,22 @@ static void syscall_exit_to_user_mode_prepare(struct pt_regs *regs)
 		syscall_exit_work(regs, cached_flags);
 }
 
-__visible noinstr void syscall_exit_to_user_mode(struct pt_regs *regs)
+static __always_inline void __syscall_exit_to_user_mode_work(struct pt_regs *regs)
 {
-	instrumentation_begin();
 	syscall_exit_to_user_mode_prepare(regs);
 	local_irq_disable_exit_to_user();
 	exit_to_user_mode_prepare(regs);
+}
+
+void syscall_exit_to_user_mode_work(struct pt_regs *regs)
+{
+	__syscall_exit_to_user_mode_work(regs);
+}
+
+__visible noinstr void syscall_exit_to_user_mode(struct pt_regs *regs)
+{
+	instrumentation_begin();
+	__syscall_exit_to_user_mode_work(regs);
 	instrumentation_end();
 	__exit_to_user_mode();
 }
-- 
2.17.1