linux-kernel - [PATCH for 4.16 06/11] Introduce sync_core_before

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Date:   Wed, 17 Jan 2018 11:54:53 -0500
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andrew Hunter <ahh@...gle.com>,
        Maged Michael <maged.michael@...il.com>,
        Avi Kivity <avi@...lladb.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Dave Watson <davejwatson@...com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andrea Parri <parri.andrea@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Greg Hackmann <ghackmann@...gle.com>,
        Will Deacon <will.deacon@....com>,
        David Sehr <sehr@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-arch@...r.kernel.org
Subject: [PATCH for 4.16 06/11] Introduce sync_core_before_usermode

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 <mathieu.desnoyers@...icios.com>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Andy Lutomirski <luto@...nel.org>
CC: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
CC: Boqun Feng <boqun.feng@...il.com>
CC: Andrew Hunter <ahh@...gle.com>
CC: Maged Michael <maged.michael@...il.com>
CC: Avi Kivity <avi@...lladb.com>
CC: Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC: Paul Mackerras <paulus@...ba.org>
CC: Michael Ellerman <mpe@...erman.id.au>
CC: Dave Watson <davejwatson@...com>
CC: Ingo Molnar <mingo@...hat.com>
CC: "H. Peter Anvin" <hpa@...or.com>
CC: Andrea Parri <parri.andrea@...il.com>
CC: Russell King <linux@...linux.org.uk>
CC: Greg Hackmann <ghackmann@...gle.com>
CC: Will Deacon <will.deacon@....com>
CC: David Sehr <sehr@...gle.com>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: x86@...nel.org
CC: linux-arch@...r.kernel.org
---
 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