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    Subject[tip:x86/asm] x86/entry: Remove unnecessary IRQ twiddling in fast 32-bit syscalls
    Commit-ID:  8b13c2552ffc8e54e57598df36707183933e8e8c
    Gitweb: http://git.kernel.org/tip/8b13c2552ffc8e54e57598df36707183933e8e8c
    Author: Andy Lutomirski <luto@kernel.org>
    AuthorDate: Mon, 5 Oct 2015 17:48:17 -0700
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Fri, 9 Oct 2015 09:41:11 +0200

    x86/entry: Remove unnecessary IRQ twiddling in fast 32-bit syscalls

    This is slightly messy, but it eliminates an unnecessary cli;sti
    pair.

    Signed-off-by: Andy Lutomirski <luto@kernel.org>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: linux-kernel@vger.kernel.org
    Link: http://lkml.kernel.org/r/22f34b1096694a37326f36c53407b8dd90f37948.1444091585.git.luto@kernel.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/entry/common.c | 18 +++++++++++-------
    1 file changed, 11 insertions(+), 7 deletions(-)

    diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
    index 0ed023d..0d1c842 100644
    --- a/arch/x86/entry/common.c
    +++ b/arch/x86/entry/common.c
    @@ -323,10 +323,10 @@ __visible void syscall_return_slowpath(struct pt_regs *regs)

    #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
    /*
    - * Does a 32-bit syscall. Called with IRQs off and does all entry and
    - * exit work.
    + * Does a 32-bit syscall. Called with IRQs on and does all entry and
    + * exit work and returns with IRQs off.
    */
    -__visible void do_int80_syscall_32(struct pt_regs *regs)
    +static void do_syscall_32_irqs_on(struct pt_regs *regs)
    {
    struct thread_info *ti = pt_regs_to_thread_info(regs);
    unsigned int nr = (unsigned int)regs->orig_ax;
    @@ -335,8 +335,6 @@ __visible void do_int80_syscall_32(struct pt_regs *regs)
    ti->status |= TS_COMPAT;
    #endif

    - local_irq_enable();
    -
    if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
    /*
    * Subtlety here: if ptrace pokes something larger than
    @@ -363,6 +361,13 @@ __visible void do_int80_syscall_32(struct pt_regs *regs)
    syscall_return_slowpath(regs);
    }

    +/* Handles int $0x80 */
    +__visible void do_int80_syscall_32(struct pt_regs *regs)
    +{
    + local_irq_enable();
    + do_syscall_32_irqs_on(regs);
    +}
    +
    /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
    __visible long do_fast_syscall_32(struct pt_regs *regs)
    {
    @@ -398,10 +403,9 @@ __visible long do_fast_syscall_32(struct pt_regs *regs)
    prepare_exit_to_usermode(regs);
    return 0; /* Keep it simple: use IRET. */
    }
    - local_irq_disable();

    /* Now this is just like a normal syscall. */
    - do_int80_syscall_32(regs);
    + do_syscall_32_irqs_on(regs);

    #ifdef CONFIG_X86_64
    /*

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