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    membarrier/x86: Provide core serializing command · 10bcc80e
    Mathieu Desnoyers 提交于
    There are two places where core serialization is needed by membarrier:
    
    1) When returning from the membarrier IPI,
    2) After scheduler updates curr to a thread with a different mm, before
       going back to user-space, since the curr->mm is used by membarrier to
       check whether it needs to send an IPI to that CPU.
    
    x86-32 uses IRET as return from interrupt, and both IRET and SYSEXIT to go
    back to user-space. The IRET instruction is core serializing, but not
    SYSEXIT.
    
    x86-64 uses IRET as return from interrupt, which takes care of the IPI.
    However, it can return to user-space through either SYSRETL (compat
    code), SYSRETQ, or IRET. Given that SYSRET{L,Q} is not core serializing,
    we rely instead on write_cr3() performed by switch_mm() to provide core
    serialization after changing the current mm, and deal with the special
    case of kthread -> uthread (temporarily keeping current mm into
    active_mm) by adding a sync_core() in that specific case.
    
    Use the new sync_core_before_usermode() to guarantee this.
    Signed-off-by: NMathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Acked-by: NThomas Gleixner <tglx@linutronix.de>
    Acked-by: NPeter 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: 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/20180129202020.8515-10-mathieu.desnoyers@efficios.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
    10bcc80e
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