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    Subject[patch V4 part 1 14/36] x86/entry: Get rid of ist_begin/end_non_atomic()
    This is completely overengineered and definitely not an interface which
    should be made available to anything else than this particular MCE case.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    ---
    arch/x86/include/asm/traps.h | 2 --
    arch/x86/kernel/cpu/mce/core.c | 6 ++++--
    arch/x86/kernel/traps.c | 37 -------------------------------------
    3 files changed, 4 insertions(+), 41 deletions(-)

    --- a/arch/x86/include/asm/traps.h
    +++ b/arch/x86/include/asm/traps.h
    @@ -120,8 +120,6 @@ asmlinkage void smp_irq_move_cleanup_int

    extern void ist_enter(struct pt_regs *regs);
    extern void ist_exit(struct pt_regs *regs);
    -extern void ist_begin_non_atomic(struct pt_regs *regs);
    -extern void ist_end_non_atomic(void);

    #ifdef CONFIG_VMAP_STACK
    void __noreturn handle_stack_overflow(const char *message,
    --- a/arch/x86/kernel/cpu/mce/core.c
    +++ b/arch/x86/kernel/cpu/mce/core.c
    @@ -1352,13 +1352,15 @@ void notrace do_machine_check(struct pt_

    /* Fault was in user mode and we need to take some action */
    if ((m.cs & 3) == 3) {
    - ist_begin_non_atomic(regs);
    + /* If this triggers there is no way to recover. Die hard. */
    + BUG_ON(!on_thread_stack() || !user_mode(regs));
    local_irq_enable();
    + preempt_enable();

    if (kill_it || do_memory_failure(&m))
    force_sig(SIGBUS);
    + preempt_disable();
    local_irq_disable();
    - ist_end_non_atomic();
    } else {
    if (!fixup_exception(regs, X86_TRAP_MC, error_code, 0))
    mce_panic("Failed kernel mode recovery", &m, msg);
    --- a/arch/x86/kernel/traps.c
    +++ b/arch/x86/kernel/traps.c
    @@ -117,43 +117,6 @@ void ist_exit(struct pt_regs *regs)
    rcu_nmi_exit();
    }

    -/**
    - * ist_begin_non_atomic() - begin a non-atomic section in an IST exception
    - * @regs: regs passed to the IST exception handler
    - *
    - * IST exception handlers normally cannot schedule. As a special
    - * exception, if the exception interrupted userspace code (i.e.
    - * user_mode(regs) would return true) and the exception was not
    - * a double fault, it can be safe to schedule. ist_begin_non_atomic()
    - * begins a non-atomic section within an ist_enter()/ist_exit() region.
    - * Callers are responsible for enabling interrupts themselves inside
    - * the non-atomic section, and callers must call ist_end_non_atomic()
    - * before ist_exit().
    - */
    -void ist_begin_non_atomic(struct pt_regs *regs)
    -{
    - BUG_ON(!user_mode(regs));
    -
    - /*
    - * Sanity check: we need to be on the normal thread stack. This
    - * will catch asm bugs and any attempt to use ist_preempt_enable
    - * from double_fault.
    - */
    - BUG_ON(!on_thread_stack());
    -
    - preempt_enable_no_resched();
    -}
    -
    -/**
    - * ist_end_non_atomic() - begin a non-atomic section in an IST exception
    - *
    - * Ends a non-atomic section started with ist_begin_non_atomic().
    - */
    -void ist_end_non_atomic(void)
    -{
    - preempt_disable();
    -}
    -
    int is_valid_bugaddr(unsigned long addr)
    {
    unsigned short ud;
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