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Commit ea530692 authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

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



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: default avatarVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
Reviewed-by: default avatarArjan 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>
parent bc83cccc

arch/x86/include/asm/processor.h

+0 −23
Original line number Diff line number Diff line
@@ -764,29 +764,6 @@ extern unsigned long idle_halt; 
extern unsigned long		idle_nomwait;

extern bool			c1e_detected;



/*

 * 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);

arch/x86/kernel/smpboot.c

+62 −1
Original line number Diff line number Diff line
@@ -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>
@@ -1383,11 +1384,71 @@ 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 */