linux-kernel - [009/101] Revert "x86, hotplug: Use mwait to offline a processor, fix the legacy case"

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Date:	Wed, 02 Nov 2011 15:25:53 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Jonathan Nieder <jrnieder@...il.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Len Brown <len.brown@...el.com>
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@...e.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@...il.com>
Cc: H. Peter Anvin <hpa@...ux.intel.com>
Cc: Len Brown <len.brown@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.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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