# \[PATCH for 4.16 06/11\] Introduce sync\_core\_before\_usermode

- From: Mathieu Desnoyers \<hidden\>
- Date: 2018-01-17 16:56:29 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2018/01/5186409
- Thread: https://ratatoskr.run/linux-api/2018/01/5186393/t.md

```text
Introduce an architecture function that ensures the current CPU
issues a core serializing instruction before returning to usermode.

This is needed for the membarrier "sync_core" command.

Architectures defining the sync_core_before_usermode() static inline
need to select ARCH_HAS_SYNC_CORE_BEFORE_USERMODE.

Signed-off-by: Mathieu Desnoyers <redacted>
CC: Thomas Gleixner <redacted>
CC: Peter Zijlstra <redacted>
CC: Andy Lutomirski <redacted>
CC: Paul E. McKenney <redacted>
CC: Boqun Feng <redacted>
CC: Andrew Hunter <redacted>
CC: Maged Michael <redacted>
CC: Avi Kivity <redacted>
CC: Benjamin Herrenschmidt <redacted>
CC: Paul Mackerras <redacted>
CC: Michael Ellerman <redacted>
CC: Dave Watson <redacted>
CC: Ingo Molnar <redacted>
CC: "H. Peter Anvin" <redacted>
CC: Andrea Parri <redacted>
CC: Russell King <redacted>
CC: Greg Hackmann <redacted>
CC: Will Deacon <redacted>
CC: David Sehr <redacted>
CC: Linus Torvalds <redacted>
CC: <redacted>
CC: <redacted>
---
 include/linux/processor.h | 6 ++++++
 init/Kconfig              | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/include/linux/processor.h b/include/linux/processor.h
index dbc952eec869..866de5326d34 100644
--- a/include/linux/processor.h
+++ b/include/linux/processor.h
@@ -68,4 +68,10 @@ do {								\
 
 #endif
 
+#ifndef CONFIG_ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
+static inline void sync_core_before_usermode(void)
+{
+}
+#endif
+
 #endif /* _LINUX_PROCESSOR_H */
diff --git a/init/Kconfig b/init/Kconfig
index 2d118b6adee2..30208da2221f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1918,3 +1918,6 @@ config ASN1
 	  functions to call on what tags.
 
 source "kernel/Kconfig.locks"
+
+config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
+	bool
-- 
2.11.0
```