[PATCH 2/4] KVM: x86: Add a VM stat exposing when SynIC AutoEOI is in use

[Alejandro Jimenez <alejandro.j.jimenez@oracle.com>]

APICv/AVIC is inhibited for guests using Hyper-V's synthetic interrupt
controller (SynIC) enlightenment, and specifically SynIC's AutoEOI feature.
It is recommended that guests do not enable AutoEOI (see flag
HV_DEPRECATING_AEOI_RECOMMENDED and commit 0f250a646382 ("KVM: x86:
hyper-v: Deactivate APICv only when AutoEOI feature is in use")), but it
can still be used in legacy configurations.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
---
 arch/x86/include/asm/kvm_host.h | 1 +
 arch/x86/kvm/hyperv.c           | 2 ++
 arch/x86/kvm/x86.c              | 3 ++-
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 12f30cb5c842..f3b40cfebec4 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1534,6 +1534,7 @@ struct kvm_vm_stat {
 	u64 nx_lpage_splits;
 	u64 max_mmu_page_hash_collisions;
 	u64 max_mmu_rmap_size;
+	u64 synic_auto_eoi_used;
 };
 
 struct kvm_vcpu_stat {
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 8a47f8541eab..4263b4ad71c5 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -149,6 +149,8 @@ static void synic_update_vector(struct kvm_vcpu_hv_synic *synic,
 					 APICV_INHIBIT_REASON_HYPERV,
 					 !!hv->synic_auto_eoi_used);
 
+	vcpu->kvm->stat.synic_auto_eoi_used = !!hv->synic_auto_eoi_used;
+
 	up_write(&vcpu->kvm->arch.apicv_update_lock);
 }
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0451c4c8d731..27e339133068 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -256,7 +256,8 @@ 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, synic_auto_eoi_used)
 };
 
 const struct kvm_stats_header kvm_vm_stats_header = {
-- 
2.39.3