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Subject[34-longterm 153/209] x86, hotplug: Use mwait to offline a processor, fix the legacy case
Date
From: H. Peter Anvin <hpa@linux.intel.com>

=====================================================================
| This is a commit scheduled for the next v2.6.34 longterm release. |
| If you see a problem with using this for longterm, please comment.|
=====================================================================

commit ea53069231f9317062910d6e772cca4ce93de8c8 upstream.

The code in native_play_dead() has a number of problems:

1. We should use MWAIT when available, to put ourselves into a deeper
sleep state.
2. We use the existence of CLFLUSH to determine if WBINVD is safe, but
that is totally bogus -- WBINVD is 486+, whereas CLFLUSH is a much
later addition.
3. We should do WBINVD inside the loop, just in case of something like
setting an A bit on page tables. Pointed out by Arjan van de Ven.

This code is based in part of a previous patch by Venki Pallipadi, but
unlike that patch this one keeps all the detection code local instead
of pre-caching a bunch of information. We're shutting down the CPU;
there is absolutely no hurry.

This patch moves all the code to C and deletes the global
wbinvd_halt() which is broken anyway.

Originally-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Reviewed-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Venkatesh Pallipadi <venki@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.hl>
LKML-Reference: <20090522232230.162239000@intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
arch/x86/include/asm/processor.h | 23 --------------
arch/x86/kernel/smpboot.c | 63 +++++++++++++++++++++++++++++++++++++-
2 files changed, 62 insertions(+), 24 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index b753ea5..6757357 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -767,29 +767,6 @@ extern unsigned long boot_option_idle_override;
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);

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 4ea2f50..d528e75 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -62,6 +62,7 @@
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/mtrr.h>
+#include <asm/mwait.h>
#include <asm/vmi.h>
#include <asm/apic.h>
#include <asm/setup.h>
@@ -1360,11 +1361,71 @@ void play_dead_common(void)
local_irq_disable();
}

+/*
+ * 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;
+
+ if (!cpu_has(&current_cpu_data, X86_FEATURE_MWAIT))
+ 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);
+ }
+
+ while (1) {
+ mb();
+ wbinvd();
+ __monitor(&current_thread_info()->flags, 0, 0);
+ mb();
+ __mwait(eax, 0);
+ }
+}
+
+static inline void hlt_play_dead(void)
+{
+ while (1) {
+ mb();
+ if (current_cpu_data.x86 >= 4)
+ wbinvd();
+ mb();
+ 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 */
--
1.7.4.4


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