[PATCH 09/23] KVM: PPC: Book3S HV: Convert ICS mutex lock to spin lock

[Paul Mackerras <paulus@samba.org>]

From: Suresh Warrier <warrier@linux.vnet.ibm.com>

Replaces the ICS mutex lock with a spin lock since we will be porting
these routines to real mode. Note that we need to disable interrupts
before we take the lock in anticipation of the fact that on the guest
side, we are running in the context of a hard irq and interrupts are
disabled (EE bit off) when the lock is acquired. Again, because we
will be acquiring the lock in hypervisor real mode, we need to use
an arch_spinlock_t instead of a normal spinlock here as we want to
avoid running any lockdep code (which may not be safe to execute in
real mode).

Signed-off-by: Suresh Warrier <warrier@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/kvm/book3s_xics.c | 68 +++++++++++++++++++++++++++++-------------
 arch/powerpc/kvm/book3s_xics.h |  2 +-
 2 files changed, 48 insertions(+), 22 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_xics.c b/arch/powerpc/kvm/book3s_xics.c
index 48f0bda..56ed9b4 100644
--- a/arch/powerpc/kvm/book3s_xics.c
+++ b/arch/powerpc/kvm/book3s_xics.c
@@ -20,6 +20,7 @@
 #include <asm/xics.h>
 #include <asm/debug.h>
 #include <asm/time.h>
+#include <asm/spinlock.h>
 
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
@@ -39,7 +40,7 @@
  * LOCKING
  * =======
  *
- * Each ICS has a mutex protecting the information about the IRQ
+ * Each ICS has a spin lock protecting the information about the IRQ
  * sources and avoiding simultaneous deliveries if the same interrupt.
  *
  * ICP operations are done via a single compare & swap transaction
@@ -109,7 +110,10 @@ static void ics_check_resend(struct kvmppc_xics *xics, struct kvmppc_ics *ics,
 {
 	int i;
 
-	mutex_lock(&ics->lock);
+	unsigned long flags;
+
+	local_irq_save(flags);
+	arch_spin_lock(&ics->lock);
 
 	for (i = 0; i < KVMPPC_XICS_IRQ_PER_ICS; i++) {
 		struct ics_irq_state *state = &ics->irq_state[i];
@@ -120,12 +124,15 @@ static void ics_check_resend(struct kvmppc_xics *xics, struct kvmppc_ics *ics,
 		XICS_DBG("resend %#x prio %#x\n", state->number,
 			      state->priority);
 
-		mutex_unlock(&ics->lock);
+		arch_spin_unlock(&ics->lock);
+		local_irq_restore(flags);
 		icp_deliver_irq(xics, icp, state->number);
-		mutex_lock(&ics->lock);
+		local_irq_save(flags);
+		arch_spin_lock(&ics->lock);
 	}
 
-	mutex_unlock(&ics->lock);
+	arch_spin_unlock(&ics->lock);
+	local_irq_restore(flags);
 }
 
 static bool write_xive(struct kvmppc_xics *xics, struct kvmppc_ics *ics,
@@ -133,8 +140,10 @@ static bool write_xive(struct kvmppc_xics *xics, struct kvmppc_ics *ics,
 		       u32 server, u32 priority, u32 saved_priority)
 {
 	bool deliver;
+	unsigned long flags;
 
-	mutex_lock(&ics->lock);
+	local_irq_save(flags);
+	arch_spin_lock(&ics->lock);
 
 	state->server = server;
 	state->priority = priority;
@@ -145,7 +154,8 @@ static bool write_xive(struct kvmppc_xics *xics, struct kvmppc_ics *ics,
 		deliver = true;
 	}
 
-	mutex_unlock(&ics->lock);
+	arch_spin_unlock(&ics->lock);
+	local_irq_restore(flags);
 
 	return deliver;
 }
@@ -186,6 +196,7 @@ int kvmppc_xics_get_xive(struct kvm *kvm, u32 irq, u32 *server, u32 *priority)
 	struct kvmppc_ics *ics;
 	struct ics_irq_state *state;
 	u16 src;
+	unsigned long flags;
 
 	if (!xics)
 		return -ENODEV;
@@ -195,10 +206,12 @@ int kvmppc_xics_get_xive(struct kvm *kvm, u32 irq, u32 *server, u32 *priority)
 		return -EINVAL;
 	state = &ics->irq_state[src];
 
-	mutex_lock(&ics->lock);
+	local_irq_save(flags);
+	arch_spin_lock(&ics->lock);
 	*server = state->server;
 	*priority = state->priority;
-	mutex_unlock(&ics->lock);
+	arch_spin_unlock(&ics->lock);
+	local_irq_restore(flags);
 
 	return 0;
 }
@@ -365,6 +378,7 @@ static void icp_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
 	struct kvmppc_ics *ics;
 	u32 reject;
 	u16 src;
+	unsigned long flags;
 
 	/*
 	 * This is used both for initial delivery of an interrupt and
@@ -391,7 +405,8 @@ static void icp_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
 	state = &ics->irq_state[src];
 
 	/* Get a lock on the ICS */
-	mutex_lock(&ics->lock);
+	local_irq_save(flags);
+	arch_spin_lock(&ics->lock);
 
 	/* Get our server */
 	if (!icp || state->server != icp->server_num) {
@@ -434,7 +449,7 @@ static void icp_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
 	 *
 	 * Note that if successful, the new delivery might have itself
 	 * rejected an interrupt that was "delivered" before we took the
-	 * icp mutex.
+	 * ics spin lock.
 	 *
 	 * In this case we do the whole sequence all over again for the
 	 * new guy. We cannot assume that the rejected interrupt is less
@@ -448,7 +463,8 @@ static void icp_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
 		 * Delivery was successful, did we reject somebody else ?
 		 */
 		if (reject && reject != XICS_IPI) {
-			mutex_unlock(&ics->lock);
+			arch_spin_unlock(&ics->lock);
+			local_irq_restore(flags);
 			new_irq = reject;
 			goto again;
 		}
@@ -468,12 +484,14 @@ static void icp_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
 		 */
 		smp_mb();
 		if (!icp->state.need_resend) {
-			mutex_unlock(&ics->lock);
+			arch_spin_unlock(&ics->lock);
+			local_irq_restore(flags);
 			goto again;
 		}
 	}
  out:
-	mutex_unlock(&ics->lock);
+	arch_spin_unlock(&ics->lock);
+	local_irq_restore(flags);
 }
 
 static void icp_down_cppr(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
@@ -880,6 +898,7 @@ static int xics_debug_show(struct seq_file *m, void *private)
 	struct kvm *kvm = xics->kvm;
 	struct kvm_vcpu *vcpu;
 	int icsid, i;
+	unsigned long flags;
 	unsigned long t_rm_kick_vcpu, t_rm_check_resend;
 	unsigned long t_rm_reject, t_rm_notify_eoi;
 
@@ -924,7 +943,8 @@ static int xics_debug_show(struct seq_file *m, void *private)
 		seq_printf(m, "=========\nICS state for ICS 0x%x\n=========\n",
 			   icsid);
 
-		mutex_lock(&ics->lock);
+		local_irq_save(flags);
+		arch_spin_lock(&ics->lock);
 
 		for (i = 0; i < KVMPPC_XICS_IRQ_PER_ICS; i++) {
 			struct ics_irq_state *irq = &ics->irq_state[i];
@@ -935,7 +955,8 @@ static int xics_debug_show(struct seq_file *m, void *private)
 				   irq->resend, irq->masked_pending);
 
 		}
-		mutex_unlock(&ics->lock);
+		arch_spin_unlock(&ics->lock);
+		local_irq_restore(flags);
 	}
 	return 0;
 }
@@ -988,7 +1009,6 @@ static struct kvmppc_ics *kvmppc_xics_create_ics(struct kvm *kvm,
 	if (!ics)
 		goto out;
 
-	mutex_init(&ics->lock);
 	ics->icsid = icsid;
 
 	for (i = 0; i < KVMPPC_XICS_IRQ_PER_ICS; i++) {
@@ -1130,13 +1150,15 @@ static int xics_get_source(struct kvmppc_xics *xics, long irq, u64 addr)
 	u64 __user *ubufp = (u64 __user *) addr;
 	u16 idx;
 	u64 val, prio;
+	unsigned long flags;
 
 	ics = kvmppc_xics_find_ics(xics, irq, &idx);
 	if (!ics)
 		return -ENOENT;
 
 	irqp = &ics->irq_state[idx];
-	mutex_lock(&ics->lock);
+	local_irq_save(flags);
+	arch_spin_lock(&ics->lock);
 	ret = -ENOENT;
 	if (irqp->exists) {
 		val = irqp->server;
@@ -1152,7 +1174,8 @@ static int xics_get_source(struct kvmppc_xics *xics, long irq, u64 addr)
 			val |= KVM_XICS_PENDING;
 		ret = 0;
 	}
-	mutex_unlock(&ics->lock);
+	arch_spin_unlock(&ics->lock);
+	local_irq_restore(flags);
 
 	if (!ret && put_user(val, ubufp))
 		ret = -EFAULT;
@@ -1169,6 +1192,7 @@ static int xics_set_source(struct kvmppc_xics *xics, long irq, u64 addr)
 	u64 val;
 	u8 prio;
 	u32 server;
+	unsigned long flags;
 
 	if (irq < KVMPPC_XICS_FIRST_IRQ || irq >= KVMPPC_XICS_NR_IRQS)
 		return -ENOENT;
@@ -1189,7 +1213,8 @@ static int xics_set_source(struct kvmppc_xics *xics, long irq, u64 addr)
 	    kvmppc_xics_find_server(xics->kvm, server) == NULL)
 		return -EINVAL;
 
-	mutex_lock(&ics->lock);
+	local_irq_save(flags);
+	arch_spin_lock(&ics->lock);
 	irqp->server = server;
 	irqp->saved_priority = prio;
 	if (val & KVM_XICS_MASKED)
@@ -1201,7 +1226,8 @@ static int xics_set_source(struct kvmppc_xics *xics, long irq, u64 addr)
 	if ((val & KVM_XICS_PENDING) && (val & KVM_XICS_LEVEL_SENSITIVE))
 		irqp->asserted = 1;
 	irqp->exists = 1;
-	mutex_unlock(&ics->lock);
+	arch_spin_unlock(&ics->lock);
+	local_irq_restore(flags);
 
 	if (val & KVM_XICS_PENDING)
 		icp_deliver_irq(xics, NULL, irqp->number);
diff --git a/arch/powerpc/kvm/book3s_xics.h b/arch/powerpc/kvm/book3s_xics.h
index de970ec..055424c 100644
--- a/arch/powerpc/kvm/book3s_xics.h
+++ b/arch/powerpc/kvm/book3s_xics.h
@@ -90,7 +90,7 @@ struct kvmppc_icp {
 };
 
 struct kvmppc_ics {
-	struct mutex lock;
+	arch_spinlock_t lock;
 	u16 icsid;
 	struct ics_irq_state irq_state[KVMPPC_XICS_IRQ_PER_ICS];
 };
-- 
2.1.4