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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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