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    Subject[009/101] Revert "x86, hotplug: Use mwait to offline a processor, fix the legacy case"
    2.6.33-longterm review patch.  If anyone has any objections, please let us know.

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

    From: Greg Kroah-Hartman <gregkh@suse.de>

    This reverts commit 226917b0735f31cf5c704e07fdd590d99bbfae58 (upstream
    ea53069231f9317062910d6e772cca4ce93de8c8 and
    a68e5c94f7d3dd64fef34dd5d97e365cae4bb42a and
    ce5f68246bf2385d6174856708d0b746dc378f20 all mushed together) as
    Jonathan Nieder reports that this causes a regression on some hardware.

    More details can be found at http://bugs.debian.org/622259

    Cc: Jonathan Nieder <jrnieder@gmail.com>
    Cc: H. Peter Anvin <hpa@linux.intel.com>
    Cc: Len Brown <len.brown@intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    arch/x86/include/asm/processor.h | 23 ++++++++++
    arch/x86/kernel/smpboot.c | 85 ---------------------------------------
    2 files changed, 24 insertions(+), 84 deletions(-)

    --- a/arch/x86/include/asm/processor.h
    +++ b/arch/x86/include/asm/processor.h
    @@ -767,6 +767,29 @@ extern unsigned long boot_option_idle_o
    extern unsigned long idle_halt;
    extern unsigned long idle_nomwait;

    +/*
    + * on systems with caches, caches must be flashed as the absolute
    + * last instruction before going into a suspended halt. Otherwise,
    + * dirty data can linger in the cache and become stale on resume,
    + * leading to strange errors.
    + *
    + * perform a variety of operations to guarantee that the compiler
    + * will not reorder instructions. wbinvd itself is serializing
    + * so the processor will not reorder.
    + *
    + * Systems without cache can just go into halt.
    + */
    +static inline void wbinvd_halt(void)
    +{
    + mb();
    + /* check for clflush to determine if wbinvd is legal */
    + if (cpu_has_clflush)
    + asm volatile("cli; wbinvd; 1: hlt; jmp 1b" : : : "memory");
    + else
    + while (1)
    + halt();
    +}
    +
    extern void enable_sep_cpu(void);
    extern int sysenter_setup(void);

    --- a/arch/x86/kernel/smpboot.c
    +++ b/arch/x86/kernel/smpboot.c
    @@ -1329,94 +1329,11 @@ void play_dead_common(void)
    local_irq_disable();
    }

    -#define MWAIT_SUBSTATE_MASK 0xf
    -#define MWAIT_SUBSTATE_SIZE 4
    -
    -#define CPUID_MWAIT_LEAF 5
    -#define CPUID5_ECX_EXTENSIONS_SUPPORTED 0x1
    -
    -/*
    - * We need to flush the caches before going to sleep, lest we have
    - * dirty data in our caches when we come back up.
    - */
    -static inline void mwait_play_dead(void)
    -{
    - unsigned int eax, ebx, ecx, edx;
    - unsigned int highest_cstate = 0;
    - unsigned int highest_subcstate = 0;
    - int i;
    - void *mwait_ptr;
    -
    - if (!cpu_has(&current_cpu_data, X86_FEATURE_MWAIT))
    - return;
    - if (!cpu_has(&current_cpu_data, X86_FEATURE_CLFLSH))
    - return;
    - if (current_cpu_data.cpuid_level < CPUID_MWAIT_LEAF)
    - return;
    -
    - eax = CPUID_MWAIT_LEAF;
    - ecx = 0;
    - native_cpuid(&eax, &ebx, &ecx, &edx);
    -
    - /*
    - * eax will be 0 if EDX enumeration is not valid.
    - * Initialized below to cstate, sub_cstate value when EDX is valid.
    - */
    - if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED)) {
    - eax = 0;
    - } else {
    - edx >>= MWAIT_SUBSTATE_SIZE;
    - for (i = 0; i < 7 && edx; i++, edx >>= MWAIT_SUBSTATE_SIZE) {
    - if (edx & MWAIT_SUBSTATE_MASK) {
    - highest_cstate = i;
    - highest_subcstate = edx & MWAIT_SUBSTATE_MASK;
    - }
    - }
    - eax = (highest_cstate << MWAIT_SUBSTATE_SIZE) |
    - (highest_subcstate - 1);
    - }
    -
    - /*
    - * This should be a memory location in a cache line which is
    - * unlikely to be touched by other processors. The actual
    - * content is immaterial as it is not actually modified in any way.
    - */
    - mwait_ptr = &current_thread_info()->flags;
    -
    - wbinvd();
    -
    - while (1) {
    - /*
    - * The CLFLUSH is a workaround for erratum AAI65 for
    - * the Xeon 7400 series. It's not clear it is actually
    - * needed, but it should be harmless in either case.
    - * The WBINVD is insufficient due to the spurious-wakeup
    - * case where we return around the loop.
    - */
    - clflush(mwait_ptr);
    - __monitor(mwait_ptr, 0, 0);
    - mb();
    - __mwait(eax, 0);
    - }
    -}
    -
    -static inline void hlt_play_dead(void)
    -{
    - if (current_cpu_data.x86 >= 4)
    - wbinvd();
    -
    - while (1) {
    - native_halt();
    - }
    -}
    -
    void native_play_dead(void)
    {
    play_dead_common();
    tboot_shutdown(TB_SHUTDOWN_WFS);
    -
    - mwait_play_dead(); /* Only returns on failure */
    - hlt_play_dead();
    + wbinvd_halt();
    }

    #else /* ... !CONFIG_HOTPLUG_CPU */



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