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Subject[PATCH] [1/139] x86, hotplug: Use mwait to offline a processor, fix the legacy case
Date
2.6.35-longterm review patch.  If anyone has any objections, please let me know.

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

From: H. Peter Anvin <hpa@linux.intel.com>

upstream ea53069231f9317062910d6e772cca4ce93de8c8
x86, hotplug: Use mwait to offline a processor, fix the legacy case

Here included also some small follow-on patches to the same code:

upstream a68e5c94f7d3dd64fef34dd5d97e365cae4bb42a
x86, hotplug: Move WBINVD back outside the play_dead loop

upstream ce5f68246bf2385d6174856708d0b746dc378f20
x86, hotplug: In the MWAIT case of play_dead, CLFLUSH the cache line

https://bugzilla.kernel.org/show_bug.cgi?id=5471

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
arch/x86/include/asm/processor.h | 23 ----------
arch/x86/kernel/smpboot.c | 85 ++++++++++++++++++++++++++++++++++++++-
2 files changed, 84 insertions(+), 24 deletions(-)

Index: linux-2.6.35.y/arch/x86/include/asm/processor.h
===================================================================
--- linux-2.6.35.y.orig/arch/x86/include/asm/processor.h
+++ linux-2.6.35.y/arch/x86/include/asm/processor.h
@@ -763,29 +763,6 @@ 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);

Index: linux-2.6.35.y/arch/x86/kernel/smpboot.c
===================================================================
--- linux-2.6.35.y.orig/arch/x86/kernel/smpboot.c
+++ linux-2.6.35.y/arch/x86/kernel/smpboot.c
@@ -1387,11 +1387,94 @@ 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);
- wbinvd_halt();
+
+ mwait_play_dead(); /* Only returns on failure */
+ hlt_play_dead();
}

#else /* ... !CONFIG_HOTPLUG_CPU */

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