[RFC 1/3] x86: KVM: stats: Add a stat to report status of APICv inhibition

[Alejandro Jimenez]

The inhibition status of APICv can currently be checked using the
'kvm_apicv_inhibit_changed' tracepoint, but this is not accessible if
tracefs is not available (e.g. kernel lockdown, non-root user). Export
inhibition status as a binary stat that can be monitored from userspace
without elevated privileges.

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/x86.c              | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ad5319a503f0..9b960a523715 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1524,6 +1524,7 @@ struct kvm_vm_stat {
 	u64 nx_lpage_splits;
 	u64 max_mmu_page_hash_collisions;
 	u64 max_mmu_rmap_size;
+	u64 apicv_inhibited;
 };
 
 struct kvm_vcpu_stat {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b66c45e7f6f8..f7f598f066e7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -255,7 +255,8 @@ const struct _kvm_stats_desc kvm_vm_stats_desc[] = {
 	STATS_DESC_ICOUNTER(VM, pages_1g),
 	STATS_DESC_ICOUNTER(VM, nx_lpage_splits),
 	STATS_DESC_PCOUNTER(VM, max_mmu_rmap_size),
-	STATS_DESC_PCOUNTER(VM, max_mmu_page_hash_collisions)
+	STATS_DESC_PCOUNTER(VM, max_mmu_page_hash_collisions),
+	STATS_DESC_IBOOLEAN(VM, apicv_inhibited)
 };
 
 const struct kvm_stats_header kvm_vm_stats_header = {
@@ -10588,6 +10589,13 @@ void __kvm_set_or_clear_apicv_inhibit(struct kvm *kvm,
 		 */
 		kvm_make_all_cpus_request(kvm, KVM_REQ_APICV_UPDATE);
 		kvm->arch.apicv_inhibit_reasons = new;
+
+		/*
+		 * Update inhibition statistic only when toggling APICv
+		 * activation status.
+		 */
+		kvm->stat.apicv_inhibited = !!new;
+
 		if (new) {
 			unsigned long gfn = gpa_to_gfn(APIC_DEFAULT_PHYS_BASE);
 			int idx = srcu_read_lock(&kvm->srcu);
-- 
2.39.3