diff mbox series

[1/3] entry: move exit to usermode functions to header file

Message ID 20231205133015.752543-2-svens@linux.ibm.com
State New
Headers
Series entry: inline syscall enter/exit functions |

Commit Message

Sven Schnelle Dec. 5, 2023, 1:30 p.m. UTC 
  To allow inlining, move exit_to_user_mode() and
exit_to_user_mode_loop() to common.h.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
---
 include/linux/entry-common.h | 95 +++++++++++++++++++++++++++++++++++-
 kernel/entry/common.c        | 89 +--------------------------------
 2 files changed, 96 insertions(+), 88 deletions(-)

Comments

Thomas Gleixner Dec. 15, 2023, 7:09 p.m. UTC | #1 
On Tue, Dec 05 2023 at 14:30, Sven Schnelle wrote:
> +/**
> + * exit_to_user_mode_loop - do any pending work before leaving to user space
> + */
> +static __always_inline unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
> +							    unsigned long ti_work)
> +{
> +	/*
> +	 * Before returning to user space ensure that all pending work
> +	 * items have been completed.
> +	 */
> +	while (ti_work & EXIT_TO_USER_MODE_WORK) {
> +
> +		local_irq_enable_exit_to_user(ti_work);
> +
> +		if (ti_work & _TIF_NEED_RESCHED)
> +			schedule();
> +
> +		if (ti_work & _TIF_UPROBE)
> +			uprobe_notify_resume(regs);
> +
> +		if (ti_work & _TIF_PATCH_PENDING)
> +			klp_update_patch_state(current);
> +
> +		if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
> +			arch_do_signal_or_restart(regs);
> +
> +		if (ti_work & _TIF_NOTIFY_RESUME)
> +			resume_user_mode_work(regs);
> +
> +		/* Architecture specific TIF work */
> +		arch_exit_to_user_mode_work(regs, ti_work);
> +
> +		/*
> +		 * Disable interrupts and reevaluate the work flags as they
> +		 * might have changed while interrupts and preemption was
> +		 * enabled above.
> +		 */
> +		local_irq_disable_exit_to_user();
> +
> +		/* Check if any of the above work has queued a deferred wakeup */
> +		tick_nohz_user_enter_prepare();
> +
> +		ti_work = read_thread_flags();
> +	}
> +
> +	/* Return the latest work state for arch_exit_to_user_mode() */
> +	return ti_work;
> +}

I'm not really sure about this part. exit_to_user_mode_loop() is the
slowpath when a TIF work flag is set. I can see the benefit on the
fastpath functions which are way smaller.

Thanks,

        tglx
Sven Schnelle Dec. 18, 2023, 7:46 a.m. UTC | #2 
Hi Thomas,

Thomas Gleixner <tglx@linutronix.de> writes:

> On Tue, Dec 05 2023 at 14:30, Sven Schnelle wrote:
>> +/**
>> + * exit_to_user_mode_loop - do any pending work before leaving to user space
>> + */
>> +static __always_inline unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
>> +							    unsigned long ti_work)
>> +{
>> +	/*
>> +	 * Before returning to user space ensure that all pending work
>> +	 * items have been completed.
>> +	 */
>> +	while (ti_work & EXIT_TO_USER_MODE_WORK) {
>> +
>> +		local_irq_enable_exit_to_user(ti_work);
>> +
>> +		if (ti_work & _TIF_NEED_RESCHED)
>> +			schedule();
>> +
>> +		if (ti_work & _TIF_UPROBE)
>> +			uprobe_notify_resume(regs);
>> +
>> +		if (ti_work & _TIF_PATCH_PENDING)
>> +			klp_update_patch_state(current);
>> +
>> +		if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
>> +			arch_do_signal_or_restart(regs);
>> +
>> +		if (ti_work & _TIF_NOTIFY_RESUME)
>> +			resume_user_mode_work(regs);
>> +
>> +		/* Architecture specific TIF work */
>> +		arch_exit_to_user_mode_work(regs, ti_work);
>> +
>> +		/*
>> +		 * Disable interrupts and reevaluate the work flags as they
>> +		 * might have changed while interrupts and preemption was
>> +		 * enabled above.
>> +		 */
>> +		local_irq_disable_exit_to_user();
>> +
>> +		/* Check if any of the above work has queued a deferred wakeup */
>> +		tick_nohz_user_enter_prepare();
>> +
>> +		ti_work = read_thread_flags();
>> +	}
>> +
>> +	/* Return the latest work state for arch_exit_to_user_mode() */
>> +	return ti_work;
>> +}
>
> I'm not really sure about this part. exit_to_user_mode_loop() is the
> slowpath when a TIF work flag is set. I can see the benefit on the
> fastpath functions which are way smaller.

Indeed, the main performance improvement comes from inlining the small
functions. As Peter mentioned the same, i sent out a v2 which doesn't
move exit_to_user_mode_loop().

Thanks!
Sven
diff mbox series

Patch

diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index d95ab85f96ba..f0f1a26dc638 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -7,6 +7,10 @@ 
 #include <linux/syscalls.h>
 #include <linux/seccomp.h>
 #include <linux/sched.h>
+#include <linux/context_tracking.h>
+#include <linux/livepatch.h>
+#include <linux/resume_user_mode.h>
+#include <linux/tick.h>
 
 #include <asm/entry-common.h>
 
@@ -258,6 +262,85 @@  static __always_inline void arch_exit_to_user_mode(void) { }
  */
 void arch_do_signal_or_restart(struct pt_regs *regs);
 
+/**
+ * exit_to_user_mode_loop - do any pending work before leaving to user space
+ */
+static __always_inline unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
+							    unsigned long ti_work)
+{
+	/*
+	 * Before returning to user space ensure that all pending work
+	 * items have been completed.
+	 */
+	while (ti_work & EXIT_TO_USER_MODE_WORK) {
+
+		local_irq_enable_exit_to_user(ti_work);
+
+		if (ti_work & _TIF_NEED_RESCHED)
+			schedule();
+
+		if (ti_work & _TIF_UPROBE)
+			uprobe_notify_resume(regs);
+
+		if (ti_work & _TIF_PATCH_PENDING)
+			klp_update_patch_state(current);
+
+		if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
+			arch_do_signal_or_restart(regs);
+
+		if (ti_work & _TIF_NOTIFY_RESUME)
+			resume_user_mode_work(regs);
+
+		/* Architecture specific TIF work */
+		arch_exit_to_user_mode_work(regs, ti_work);
+
+		/*
+		 * Disable interrupts and reevaluate the work flags as they
+		 * might have changed while interrupts and preemption was
+		 * enabled above.
+		 */
+		local_irq_disable_exit_to_user();
+
+		/* Check if any of the above work has queued a deferred wakeup */
+		tick_nohz_user_enter_prepare();
+
+		ti_work = read_thread_flags();
+	}
+
+	/* Return the latest work state for arch_exit_to_user_mode() */
+	return ti_work;
+}
+
+/**
+ * exit_to_user_mode_prepare - call exit_to_user_mode_loop() if required
+ *
+ * 1) check that interrupts are disabled
+ * 2) call tick_nohz_user_enter_prepare()
+ * 3) call exit_to_user_mode_loop() if any flags from
+ *    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)
+{
+	unsigned long ti_work;
+
+	lockdep_assert_irqs_disabled();
+
+	/* Flush pending rcuog wakeup before the last need_resched() check */
+	tick_nohz_user_enter_prepare();
+
+	ti_work = read_thread_flags();
+	if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
+		ti_work = exit_to_user_mode_loop(regs, ti_work);
+
+	arch_exit_to_user_mode_prepare(regs, ti_work);
+
+	/* Ensure that kernel state is sane for a return to userspace */
+	kmap_assert_nomap();
+	lockdep_assert_irqs_disabled();
+	lockdep_sys_exit();
+}
+
 /**
  * exit_to_user_mode - Fixup state when exiting to user mode
  *
@@ -276,7 +359,17 @@  void arch_do_signal_or_restart(struct pt_regs *regs);
  * non-instrumentable.
  * The caller has to invoke syscall_exit_to_user_mode_work() before this.
  */
-void exit_to_user_mode(void);
+static __always_inline void exit_to_user_mode(void)
+{
+	instrumentation_begin();
+	trace_hardirqs_on_prepare();
+	lockdep_hardirqs_on_prepare();
+	instrumentation_end();
+
+	user_enter_irqoff();
+	arch_exit_to_user_mode();
+	lockdep_hardirqs_on(CALLER_ADDR0);
+}
 
 /**
  * syscall_exit_to_user_mode_work - Handle work before returning to user mode
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index d7ee4bc3f2ba..6ba2bcfbe32c 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -123,94 +123,9 @@  noinstr void syscall_enter_from_user_mode_prepare(struct pt_regs *regs)
 	instrumentation_end();
 }
 
-/* See comment for exit_to_user_mode() in entry-common.h */
-static __always_inline void __exit_to_user_mode(void)
-{
-	instrumentation_begin();
-	trace_hardirqs_on_prepare();
-	lockdep_hardirqs_on_prepare();
-	instrumentation_end();
-
-	user_enter_irqoff();
-	arch_exit_to_user_mode();
-	lockdep_hardirqs_on(CALLER_ADDR0);
-}
-
-void noinstr exit_to_user_mode(void)
-{
-	__exit_to_user_mode();
-}
-
 /* Workaround to allow gradual conversion of architecture code */
 void __weak arch_do_signal_or_restart(struct pt_regs *regs) { }
 
-static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
-					    unsigned long ti_work)
-{
-	/*
-	 * Before returning to user space ensure that all pending work
-	 * items have been completed.
-	 */
-	while (ti_work & EXIT_TO_USER_MODE_WORK) {
-
-		local_irq_enable_exit_to_user(ti_work);
-
-		if (ti_work & _TIF_NEED_RESCHED)
-			schedule();
-
-		if (ti_work & _TIF_UPROBE)
-			uprobe_notify_resume(regs);
-
-		if (ti_work & _TIF_PATCH_PENDING)
-			klp_update_patch_state(current);
-
-		if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
-			arch_do_signal_or_restart(regs);
-
-		if (ti_work & _TIF_NOTIFY_RESUME)
-			resume_user_mode_work(regs);
-
-		/* Architecture specific TIF work */
-		arch_exit_to_user_mode_work(regs, ti_work);
-
-		/*
-		 * Disable interrupts and reevaluate the work flags as they
-		 * might have changed while interrupts and preemption was
-		 * enabled above.
-		 */
-		local_irq_disable_exit_to_user();
-
-		/* Check if any of the above work has queued a deferred wakeup */
-		tick_nohz_user_enter_prepare();
-
-		ti_work = read_thread_flags();
-	}
-
-	/* Return the latest work state for arch_exit_to_user_mode() */
-	return ti_work;
-}
-
-static void exit_to_user_mode_prepare(struct pt_regs *regs)
-{
-	unsigned long ti_work;
-
-	lockdep_assert_irqs_disabled();
-
-	/* Flush pending rcuog wakeup before the last need_resched() check */
-	tick_nohz_user_enter_prepare();
-
-	ti_work = read_thread_flags();
-	if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK))
-		ti_work = exit_to_user_mode_loop(regs, ti_work);
-
-	arch_exit_to_user_mode_prepare(regs, ti_work);
-
-	/* Ensure that kernel state is sane for a return to userspace */
-	kmap_assert_nomap();
-	lockdep_assert_irqs_disabled();
-	lockdep_sys_exit();
-}
-
 /*
  * If SYSCALL_EMU is set, then the only reason to report is when
  * SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP).  This syscall
@@ -295,7 +210,7 @@  __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();
+	exit_to_user_mode();
 }
 
 noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs)
@@ -308,7 +223,7 @@  noinstr void irqentry_exit_to_user_mode(struct pt_regs *regs)
 	instrumentation_begin();
 	exit_to_user_mode_prepare(regs);
 	instrumentation_end();
-	__exit_to_user_mode();
+	exit_to_user_mode();
 }
 
 noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)