Commit 9043442b authored by Juergen Gross's avatar Juergen Gross Committed by Ingo Molnar
Browse files

locking/paravirt: Use new static key for controlling call of virt_spin_lock() 



There are cases where a guest tries to switch spinlocks to bare metal
behavior (e.g. by setting "xen_nopvspin" boot parameter). Today this
has the downside of falling back to unfair test and set scheme for
qspinlocks due to virt_spin_lock() detecting the virtualized
environment.

Add a static key controlling whether virt_spin_lock() should be
called or not. When running on bare metal set the new key to false.

Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarWaiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akataria@vmware.com
Cc: boris.ostrovsky@oracle.com
Cc: chrisw@sous-sol.org
Cc: hpa@zytor.com
Cc: jeremy@goop.org
Cc: rusty@rustcorp.com.au
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/20170906173625.18158-2-jgross@suse.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent af1a34f2

arch/x86/include/asm/qspinlock.h

+10 −1
Original line number Diff line number Diff line 
#ifndef _ASM_X86_QSPINLOCK_H

#define _ASM_X86_QSPINLOCK_H



#include <linux/jump_label.h>

#include <asm/cpufeature.h>

#include <asm-generic/qspinlock_types.h>

#include <asm/paravirt.h>
@@ -46,10 +47,14 @@ static inline void queued_spin_unlock(struct qspinlock *lock) 
#endif



#ifdef CONFIG_PARAVIRT

DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key);



void native_pv_lock_init(void) __init;



#define virt_spin_lock virt_spin_lock

static inline bool virt_spin_lock(struct qspinlock *lock)

{

	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))

	if (!static_branch_likely(&virt_spin_lock_key))

		return false;



	/*
@@ -65,6 +70,10 @@ static inline bool virt_spin_lock(struct qspinlock *lock) 


	return true;

}

#else

static inline void native_pv_lock_init(void)

{

}

#endif /* CONFIG_PARAVIRT */



#include <asm-generic/qspinlock.h>

arch/x86/kernel/paravirt.c

+12 −2
Original line number Diff line number Diff line
@@ -115,8 +115,18 @@ unsigned paravirt_patch_jmp(void *insnbuf, const void *target, 
	return 5;

}



/* Neat trick to map patch type back to the call within the

 * corresponding structure. */

DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key);



void __init native_pv_lock_init(void)

{

	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))

		static_branch_disable(&virt_spin_lock_key);

}



/*

 * Neat trick to map patch type back to the call within the

 * corresponding structure.

 */

static void *get_call_destination(u8 type)

{

	struct paravirt_patch_template tmpl = {

arch/x86/kernel/smpboot.c

+2 −0
Original line number Diff line number Diff line
@@ -77,6 +77,7 @@ 
#include <asm/i8259.h>

#include <asm/realmode.h>

#include <asm/misc.h>

#include <asm/qspinlock.h>



/* Number of siblings per CPU package */

int smp_num_siblings = 1;
@@ -1384,6 +1385,7 @@ void __init native_smp_prepare_boot_cpu(void) 
	/* already set me in cpu_online_mask in boot_cpu_init() */

	cpumask_set_cpu(me, cpu_callout_mask);

	cpu_set_state_online(me);

	native_pv_lock_init();

}



void __init native_smp_cpus_done(unsigned int max_cpus)

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