[Xen-devel] [PATCH v16 10/14] pvqspinlock, x86: Enable PV qspinlock for KVM

[Waiman Long <Waiman.Long@xxxxxx>]

This patch adds the necessary KVM specific code to allow KVM to
support the CPU halting and kicking operations needed by the queue
spinlock PV code.

Signed-off-by: Waiman Long <Waiman.Long@xxxxxx>
---
 arch/x86/kernel/kvm.c |   43 +++++++++++++++++++++++++++++++++++++++++++
 kernel/Kconfig.locks  |    2 +-
 2 files changed, 44 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index e354cc6..4bb42c0 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -584,6 +584,39 @@ static void kvm_kick_cpu(int cpu)
        kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
 }
 
+
+#ifdef CONFIG_QUEUE_SPINLOCK
+
+#include <asm/qspinlock.h>
+
+static void kvm_wait(u8 *ptr, u8 val)
+{
+       unsigned long flags;
+
+       if (in_nmi())
+               return;
+
+       local_irq_save(flags);
+
+       if (READ_ONCE(*ptr) != val)
+               goto out;
+
+       /*
+        * halt until it's our turn and kicked. Note that we do safe halt
+        * for irq enabled case to avoid hang when lock info is overwritten
+        * in irq spinlock slowpath and no spurious interrupt occur to save us.
+        */
+       if (arch_irqs_disabled_flags(flags))
+               halt();
+       else
+               safe_halt();
+
+out:
+       local_irq_restore(flags);
+}
+
+#else /* !CONFIG_QUEUE_SPINLOCK */
+
 enum kvm_contention_stat {
        TAKEN_SLOW,
        TAKEN_SLOW_PICKUP,
@@ -817,6 +850,8 @@ static void kvm_unlock_kick(struct arch_spinlock *lock, 
__ticket_t ticket)
        }
 }
 
+#endif /* !CONFIG_QUEUE_SPINLOCK */
+
 /*
  * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
  */
@@ -828,8 +863,16 @@ void __init kvm_spinlock_init(void)
        if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
                return;
 
+#ifdef CONFIG_QUEUE_SPINLOCK
+       __pv_init_lock_hash();
+       pv_lock_ops.queue_spin_lock_slowpath = __pv_queue_spin_lock_slowpath;
+       pv_lock_ops.queue_spin_unlock = PV_CALLEE_SAVE(__pv_queue_spin_unlock);
+       pv_lock_ops.wait = kvm_wait;
+       pv_lock_ops.kick = kvm_kick_cpu;
+#else /* !CONFIG_QUEUE_SPINLOCK */
        pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
        pv_lock_ops.unlock_kick = kvm_unlock_kick;
+#endif
 }
 
 static __init int kvm_spinlock_init_jump(void)
diff --git a/kernel/Kconfig.locks b/kernel/Kconfig.locks
index c6a8f7c..537b13e 100644
--- a/kernel/Kconfig.locks
+++ b/kernel/Kconfig.locks
@@ -240,7 +240,7 @@ config ARCH_USE_QUEUE_SPINLOCK
 
 config QUEUE_SPINLOCK
        def_bool y if ARCH_USE_QUEUE_SPINLOCK
-       depends on SMP && !PARAVIRT_SPINLOCKS
+       depends on SMP && (!PARAVIRT_SPINLOCKS || !XEN)
 
 config ARCH_USE_QUEUE_RWLOCK
        bool
-- 
1.7.1


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