write in 30M

hc

2024-02-20 ea08eeccae9297f7aabd2ef7f0c2517ac4549acc

 kernel/arch/x86/include/asm/qspinlock.h
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@@ -11,20 +11,17 @@
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 #define _Q_PENDING_LOOPS	(1 << 9)
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 #define queued_fetch_set_pending_acquire queued_fetch_set_pending_acquire
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-
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-static __always_inline bool __queued_RMW_btsl(struct qspinlock *lock)
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-{
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-	GEN_BINARY_RMWcc(LOCK_PREFIX "btsl", lock->val.counter,
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-			 "I", _Q_PENDING_OFFSET, "%0", c);
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-}
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-
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 static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lock)
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 {
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-	u32 val = 0;
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+	u32 val;
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-	if (__queued_RMW_btsl(lock))
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-		val |= _Q_PENDING_VAL;
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-
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+	/*
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+	 * We can't use GEN_BINARY_RMWcc() inside an if() stmt because asm goto
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+	 * and CONFIG_PROFILE_ALL_BRANCHES=y results in a label inside a
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+	 * statement expression, which GCC doesn't like.
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+	 */
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+	val = GEN_BINARY_RMWcc(LOCK_PREFIX "btsl", lock->val.counter, c,
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+			       "I", _Q_PENDING_OFFSET) * _Q_PENDING_VAL;
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 	val |= atomic_read(&lock->val) & ~_Q_PENDING_MASK;
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 	return val;
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@@ -35,6 +32,7 @@
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 extern void __pv_init_lock_hash(void);
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 extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
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 extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock *lock);
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+extern bool nopvspin;
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 #define	queued_spin_unlock queued_spin_unlock
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 /**
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@@ -66,10 +64,25 @@
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 #endif
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 #ifdef CONFIG_PARAVIRT
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+/*
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+ * virt_spin_lock_key - enables (by default) the virt_spin_lock() hijack.
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+ *
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+ * Native (and PV wanting native due to vCPU pinning) should disable this key.
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+ * It is done in this backwards fashion to only have a single direction change,
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+ * which removes ordering between native_pv_spin_init() and HV setup.
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+ */
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 DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key);
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 void native_pv_lock_init(void) __init;
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+/*
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+ * Shortcut for the queued_spin_lock_slowpath() function that allows
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+ * virt to hijack it.
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+ *
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+ * Returns:
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+ *   true - lock has been negotiated, all done;
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+ *   false - queued_spin_lock_slowpath() will do its thing.
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+ */
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 #define virt_spin_lock virt_spin_lock
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 static inline bool virt_spin_lock(struct qspinlock *lock)
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 {