[PATCH 3/3 v3] KVM: x86: Add a new VM statistic to show number of VCPUs created in a given VM

[Krish Sadhukhan <krish.sadhukhan@oracle.com>]

'struct kvm' already has a member for tracking the number of VCPUs created
in a given VM. Add this as a new VM statistic to KVM debugfs. This statistic
can be a useful metric to track the usage of VCPUs on a host running
customer VMs.

Signed-off-by: Krish Sadhukhan <Krish.Sadhukhan@oracle.com>
---
 arch/x86/include/asm/kvm_host.h | 1 +
 arch/x86/kvm/x86.c              | 1 +
 virt/kvm/kvm_main.c             | 2 ++
 3 files changed, 4 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f6d5387bb88f..8f61a3fc3d39 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1138,6 +1138,7 @@ struct kvm_vm_stat {
 	ulong lpages;
 	ulong nx_lpage_splits;
 	ulong max_mmu_page_hash_collisions;
+	ulong vcpus;
 };
 
 struct kvm_vcpu_stat {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index baa953757911..7a1ff3052488 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -258,6 +258,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
 	VM_STAT("largepages", lpages, .mode = 0444),
 	VM_STAT("nx_largepages_splitted", nx_lpage_splits, .mode = 0444),
 	VM_STAT("max_mmu_page_hash_collisions", max_mmu_page_hash_collisions),
+	VM_STAT("vcpus", vcpus),
 	{ NULL }
 };
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6b4feb92dc79..d910e4020a43 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3318,6 +3318,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
 	}
 
 	kvm->created_vcpus++;
+	kvm->stat.vcpus++;
 	mutex_unlock(&kvm->lock);
 
 	r = kvm_arch_vcpu_precreate(kvm, id);
@@ -3394,6 +3395,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
 vcpu_decrement:
 	mutex_lock(&kvm->lock);
 	kvm->created_vcpus--;
+	kvm->stat.vcpus--;
 	mutex_unlock(&kvm->lock);
 	return r;
 }
-- 
2.27.0