[PATCH 3/4 v2] KVM: nVMX: nSVM: Add a new debugfs statistic to show how many VCPUs have run nested guests

[Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>]

Add a new debugfs statistic to show how many VCPUs have run nested guests.
This statistic considers only the first time a given VCPU successfully runs
a nested guest.

Signed-off-by: Krish Sadhukhan <Krish.Sadhukhan@xxxxxxxxxx>
Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h | 1 +
 arch/x86/kvm/svm/svm.c          | 5 ++++-
 arch/x86/kvm/vmx/vmx.c          | 5 ++++-
 arch/x86/kvm/x86.c              | 1 +
 4 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index cf8557b2b90f..a19fe2cfaa93 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_ran_nested;
 };
 
 struct kvm_vcpu_stat {
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 57c351640355..d1871c51411f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3876,8 +3876,11 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
 		/* Track VMRUNs that have made past consistency checking */
 		if (svm->nested.nested_run_pending &&
 		    svm->vmcb->control.exit_code != SVM_EXIT_ERR &&
-		    svm->vmcb->control.exit_code != SVM_EXIT_NPF)
+		    svm->vmcb->control.exit_code != SVM_EXIT_NPF) {
+			if (!vcpu->stat.nested_runs)
+				++vcpu->kvm->stat.vcpus_ran_nested;
                         ++vcpu->stat.nested_runs;
+		}
 
 		svm->nested.nested_run_pending = 0;
 	}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index fa8df7ab2756..dc29aa926be6 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6845,8 +6845,11 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
 		 * checking.
 		 */
 		if (vmx->nested.nested_run_pending &&
-		    !vmx->exit_reason.failed_vmentry)
+		    !vmx->exit_reason.failed_vmentry) {
+			if (!vcpu->stat.nested_runs)
+				++vcpu->kvm->stat.vcpus_ran_nested;
 			++vcpu->stat.nested_runs;
+		}
 
 		vmx->nested.nested_run_pending = 0;
 	}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6d1f51f6c344..cbca3609a152 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -257,6 +257,7 @@ 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_ran_nested", vcpus_ran_nested),
 	{ NULL }
 };
 
-- 
2.27.0