KVM: PPC: Fix issue clearing exit timing counters

Following dump is observed on host when clearing the exit timing counters

[root@p1021mds kvm]# echo -n 'c' > vm1200_vcpu0_timing
INFO: task echo:1276 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
echo          D 0ff5bf94     0  1276   1190 0x00000000
Call Trace:
[c2157e40] [c0007908] __switch_to+0x9c/0xc4
[c2157e50] [c040293c] schedule+0x1b4/0x3bc
[c2157e90] [c04032dc] __mutex_lock_slowpath+0x74/0xc0
[c2157ec0] [c00369e4] kvmppc_init_timing_stats+0x20/0xb8
[c2157ed0] [c0036b00] kvmppc_exit_timing_write+0x84/0x98
[c2157ef0] [c00b9f90] vfs_write+0xc0/0x16c
[c2157f10] [c00ba284] sys_write+0x4c/0x90
[c2157f40] [c000e320] ret_from_syscall+0x0/0x3c

        The vcpu->mutex is used by kvm_ioctl_* (KVM_RUN etc) and same was
used when clearing the stats (in kvmppc_init_timing_stats()). What happens
is that when the guest is idle then it held the vcpu->mutx. While the
exiting timing process waits for guest to release the vcpu->mutex and
a hang state is reached.

        Now using seprate lock for exit timing stats.

Signed-off-by: Bharat Bhushan <Bharat.Bhushan@freescale.com>
Acked-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/powerpc/include/asm/kvm_host.h

@@ -255,6 +255,7 @@ struct kvm_vcpu_arch {
 	u32 dbsr;
 
 #ifdef CONFIG_KVM_EXIT_TIMING
+	struct mutex exit_timing_lock;
 	struct kvmppc_exit_timing timing_exit;
 	struct kvmppc_exit_timing timing_last_enter;
 	u32 last_exit_type;

arch/powerpc/kvm/powerpc.c

@@ -284,6 +284,10 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 	tasklet_init(&vcpu->arch.tasklet, kvmppc_decrementer_func, (ulong)vcpu);
 	vcpu->arch.dec_timer.function = kvmppc_decrementer_wakeup;
 
+#ifdef CONFIG_KVM_EXIT_TIMING
+	mutex_init(&vcpu->arch.exit_timing_lock);
+#endif
+
 	return 0;
 }
 

arch/powerpc/kvm/timing.c

@@ -34,8 +34,8 @@ void kvmppc_init_timing_stats(struct kvm_vcpu *vcpu)
 {
 	int i;
 
-	/* pause guest execution to avoid concurrent updates */
-	mutex_lock(&vcpu->mutex);
+	/* Take a lock to avoid concurrent updates */
+	mutex_lock(&vcpu->arch.exit_timing_lock);
 
 	vcpu->arch.last_exit_type = 0xDEAD;
 	for (i = 0; i < __NUMBER_OF_KVM_EXIT_TYPES; i++) {
@@ -49,7 +49,7 @@ void kvmppc_init_timing_stats(struct kvm_vcpu *vcpu)
 	vcpu->arch.timing_exit.tv64 = 0;
 	vcpu->arch.timing_last_enter.tv64 = 0;
 
-	mutex_unlock(&vcpu->mutex);
+	mutex_unlock(&vcpu->arch.exit_timing_lock);
 }
 
 static void add_exit_timing(struct kvm_vcpu *vcpu, u64 duration, int type)
@@ -65,6 +65,8 @@ static void add_exit_timing(struct kvm_vcpu *vcpu, u64 duration, int type)
 		return;
 	}
 
+	mutex_lock(&vcpu->arch.exit_timing_lock);
+
 	vcpu->arch.timing_count_type[type]++;
 
 	/* sum */
@@ -93,6 +95,8 @@ static void add_exit_timing(struct kvm_vcpu *vcpu, u64 duration, int type)
 		vcpu->arch.timing_min_duration[type] = duration;
 	if (unlikely(duration > vcpu->arch.timing_max_duration[type]))
 		vcpu->arch.timing_max_duration[type] = duration;
+
+	mutex_unlock(&vcpu->arch.exit_timing_lock);
 }
 
 void kvmppc_update_timing_stats(struct kvm_vcpu *vcpu)