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Commit 09000adb authored by Bharat Bhushan's avatar Bharat Bhushan Committed by Avi Kivity
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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: default avatarBharat Bhushan <Bharat.Bhushan@freescale.com>
Acked-by: default avatarAlexander Graf <agraf@suse.de>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 7c562522

arch/powerpc/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -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

+4 −0
Original line number Diff line number Diff line
@@ -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

+7 −3
Original line number Diff line number Diff line
@@ -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)