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    Subject[PATCH 3.16 222/254] x86/mce: Make machine check speculation protected
    3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Thomas Gleixner <tglx@linutronix.de>

    commit 6f41c34d69eb005e7848716bbcafc979b35037d5 upstream.

    The machine check idtentry uses an indirect branch directly from the low
    level code. This evades the speculation protection.

    Replace it by a direct call into C code and issue the indirect call there
    so the compiler can apply the proper speculation protection.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Reviewed-by:Borislav Petkov <bp@alien8.de>
    Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
    Niced-by: Peter Zijlstra <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801181626290.1847@nanos
    [bwh: Backported to 3.16
    - #include <asm/traps.h> in mce.c
    - Adjust filename, context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    --- a/arch/x86/include/asm/traps.h
    +++ b/arch/x86/include/asm/traps.h
    @@ -91,6 +91,7 @@ dotraplinkage void do_simd_coprocessor_e
    #ifdef CONFIG_X86_32
    dotraplinkage void do_iret_error(struct pt_regs *, long);
    #endif
    +dotraplinkage void do_mce(struct pt_regs *, long);

    static inline int get_si_code(unsigned long condition)
    {
    --- a/arch/x86/kernel/cpu/mcheck/mce.c
    +++ b/arch/x86/kernel/cpu/mcheck/mce.c
    @@ -46,6 +46,7 @@
    #include <asm/tlbflush.h>
    #include <asm/mce.h>
    #include <asm/msr.h>
    +#include <asm/traps.h>

    #include "mce-internal.h"

    @@ -1693,6 +1694,11 @@ static void unexpected_machine_check(str
    void (*machine_check_vector)(struct pt_regs *, long error_code) =
    unexpected_machine_check;

    +dotraplinkage void do_mce(struct pt_regs *regs, long error_code)
    +{
    + machine_check_vector(regs, error_code);
    +}
    +
    /*
    * Called for each booted CPU to set up machine checks.
    * Must be called with preempt off:
    --- a/arch/x86/kernel/entry_64.S
    +++ b/arch/x86/kernel/entry_64.S
    @@ -1320,7 +1320,7 @@ trace_idtentry page_fault do_page_fault
    idtentry async_page_fault do_async_page_fault has_error_code=1
    #endif
    #ifdef CONFIG_X86_MCE
    -idtentry machine_check has_error_code=0 paranoid=1 do_sym=*machine_check_vector(%rip)
    +idtentry machine_check do_mce has_error_code=0 paranoid=1
    #endif

    /*
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