linux-kernel - [RFC PATCH 1/2] x86: Introduce sync_core_before

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Message-Id: <20171110211249.10742-2-mathieu.desnoyers@efficios.com>
Date:   Fri, 10 Nov 2017 16:12:48 -0500
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.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: [RFC PATCH 1/2] x86: 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 to fix an existing core serialization bug on
thread migration, and also needed by the membarrier "sync_core" command.

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

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
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: Thomas Gleixner <tglx@...utronix.de>
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
---
 arch/x86/Kconfig                 |  1 +
 arch/x86/include/asm/processor.h | 10 ++++++++++
 include/linux/processor.h        |  6 ++++++
 3 files changed, 17 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 01f78c1d40b5..54fbb8960d94 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -62,6 +62,7 @@ config X86
 	select ARCH_HAS_SG_CHAIN
 	select ARCH_HAS_STRICT_KERNEL_RWX
 	select ARCH_HAS_STRICT_MODULE_RWX
+	select ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
 	select ARCH_HAS_ZONE_DEVICE		if X86_64
 	select ARCH_HAVE_NMI_SAFE_CMPXCHG
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index bdac19ab2488..6ce996a7c730 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -706,6 +706,16 @@ static inline void sync_core(void)
 #endif
 }
 
+/*
+ * Ensure that a core serializing instruction is issued before returning
+ * to user-mode. x86 implements return to user-space through sysexit and
+ * sysretq, which are not core serializing.
+ */
+static inline void sync_core_before_usermode(void)
+{
+	sync_core();
+}
+
 extern void select_idle_routine(const struct cpuinfo_x86 *c);
 extern void amd_e400_c1e_apic_setup(void);
 
diff --git a/include/linux/processor.h b/include/linux/processor.h
index dbc952eec869..7d12e6fa050e 100644
--- a/include/linux/processor.h
+++ b/include/linux/processor.h
@@ -68,4 +68,10 @@ do {								\
 
 #endif
 
+#ifndef ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
+static inline sync_core_before_usermode(void)
+{
+}
+#endif
+
 #endif /* _LINUX_PROCESSOR_H */
-- 
2.11.0