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locking/qspinlock,x86: Clarify virt_spin_lock_key 

Add a few comments to clarify how this is supposed to work.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juergen Gross <jgross@suse.com>
This commit is contained in:
Peter Zijlstra 2019-08-01 15:30:28 +02:00
parent fce45cd411
commit 24a376d651
1 changed files with 15 additions and 0 deletions
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15
arch/x86/include/asm/qspinlock.h
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@ -63,10 +63,25 @@ static inline bool vcpu_is_preempted(long cpu)
#endif
#ifdef CONFIG_PARAVIRT
/*
* virt_spin_lock_key - enables (by default) the virt_spin_lock() hijack.
*
* Native (and PV wanting native due to vCPU pinning) should disable this key.
* It is done in this backwards fashion to only have a single direction change,
* which removes ordering between native_pv_spin_init() and HV setup.
*/
DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key);
void native_pv_lock_init(void) __init;
/*
* Shortcut for the queued_spin_lock_slowpath() function that allows
* virt to hijack it.
*
* Returns:
* true - lock has been negotiated, all done;
* false - queued_spin_lock_slowpath() will do its thing.
*/
#define virt_spin_lock virt_spin_lock
static inline bool virt_spin_lock(struct qspinlock *lock)
{