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    Subject[tip:sched/urgent] locking: Introduce sync_core_before_usermode()
    Commit-ID:  e61938a921a46347d7725badc40ec436ebfff977
    Gitweb: https://git.kernel.org/tip/e61938a921a46347d7725badc40ec436ebfff977
    Author: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    AuthorDate: Mon, 29 Jan 2018 15:20:15 -0500
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Mon, 5 Feb 2018 21:34:50 +0100

    locking: 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@efficios.com>
    Acked-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Andrea Parri <parri.andrea@gmail.com>
    Cc: Andrew Hunter <ahh@google.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Avi Kivity <avi@scylladb.com>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Boqun Feng <boqun.feng@gmail.com>
    Cc: Dave Watson <davejwatson@fb.com>
    Cc: David Sehr <sehr@google.com>
    Cc: Greg Hackmann <ghackmann@google.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Maged Michael <maged.michael@gmail.com>
    Cc: Michael Ellerman <mpe@ellerman.id.au>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Russell King <linux@armlinux.org.uk>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: linux-api@vger.kernel.org
    Cc: linux-arch@vger.kernel.org
    Link: http://lkml.kernel.org/r/20180129202020.8515-7-mathieu.desnoyers@efficios.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    include/linux/sync_core.h | 21 +++++++++++++++++++++
    init/Kconfig | 3 +++
    2 files changed, 24 insertions(+)

    diff --git a/include/linux/sync_core.h b/include/linux/sync_core.h
    new file mode 100644
    index 0000000..013da4b
    --- /dev/null
    +++ b/include/linux/sync_core.h
    @@ -0,0 +1,21 @@
    +/* SPDX-License-Identifier: GPL-2.0 */
    +#ifndef _LINUX_SYNC_CORE_H
    +#define _LINUX_SYNC_CORE_H
    +
    +#ifdef CONFIG_ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
    +#include <asm/sync_core.h>
    +#else
    +/*
    + * This is a dummy sync_core_before_usermode() implementation that can be used
    + * on all architectures which return to user-space through core serializing
    + * instructions.
    + * If your architecture returns to user-space through non-core-serializing
    + * instructions, you need to write your own functions.
    + */
    +static inline void sync_core_before_usermode(void)
    +{
    +}
    +#endif
    +
    +#endif /* _LINUX_SYNC_CORE_H */
    +
    diff --git a/init/Kconfig b/init/Kconfig
    index 837adcf..535421f 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
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