locking/pvqspinlock, x86: Enable PV qspinlock for KVM

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@hp.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Daniel J Blueman <daniel@numascale.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paolo Bonzini <paolo.bonzini@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1429901803-29771-11-git-send-email-Waiman.Long@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 44 insertions, 1 deletions

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 9435620062df..6c21d931bd24 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_QUEUED_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_QUEUED_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_QUEUED_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_QUEUED_SPINLOCK
+        __pv_init_lock_hash();
+        pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
+        pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
+        pv_lock_ops.wait = kvm_wait;
+        pv_lock_ops.kick = kvm_kick_cpu;
+#else /* !CONFIG_QUEUED_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 95fdad866a98..4379eef9334d 100644
--- a/kernel/Kconfig.locks
+++ b/kernel/Kconfig.locks
@@ -240,7 +240,7 @@ config ARCH_USE_QUEUED_SPINLOCK
 
 config QUEUED_SPINLOCK
         def_bool y if ARCH_USE_QUEUED_SPINLOCK
-        depends on SMP && !PARAVIRT_SPINLOCKS
+        depends on SMP && (!PARAVIRT_SPINLOCKS || !XEN)
 
 config ARCH_USE_QUEUE_RWLOCK
         bool