[PATCH] x86/kvm/hyper-v: Don't deactivate APICv unconditionally when Hyper-V SynIC enabled

[junjiehua0xff]

From: Junjie Hua <junjiehua@xxxxxxxxxxx>

The current implementation of Hyper-V SynIC[1] request to deactivate 
APICv when SynIC is enabled, since the AutoEOI feature of SynIC is not 
compatible with APICv[2].

Actually, windows doesn't use AutoEOI if deprecating AutoEOI bit is set 
(CPUID.40000004H:EAX[bit 9], HyperV-TLFS v6.0b section 2.4.5), we don't 
need to disable APICv in this case.

[1] commit 5c919412fe61 ("kvm/x86: Hyper-V synthetic interrupt controller")
[2] https://patchwork.kernel.org/patch/7486761/

Signed-off-by: Junjie Hua <junjiehua@xxxxxxxxxxx>
---
 arch/x86/kvm/hyperv.c | 18 +++++++++++++++++-
 arch/x86/kvm/lapic.c  |  3 +++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 5c7c406..9eee2da 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -899,6 +899,19 @@ void kvm_hv_vcpu_postcreate(struct kvm_vcpu *vcpu)
 	hv_vcpu->vp_index = kvm_vcpu_get_idx(vcpu);
 }
 
+static bool kvm_hv_is_synic_autoeoi_deprecated(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpuid_entry2 *entry;
+
+	entry = kvm_find_cpuid_entry(vcpu,
+				HYPERV_CPUID_ENLIGHTMENT_INFO,
+				0);
+	if (!entry)
+		return false;
+
+	return entry->eax & HV_DEPRECATING_AEOI_RECOMMENDED;
+}
+
 int kvm_hv_activate_synic(struct kvm_vcpu *vcpu, bool dont_zero_synic_pages)
 {
 	struct kvm_vcpu_hv_synic *synic = vcpu_to_synic(vcpu);
@@ -908,7 +921,10 @@ int kvm_hv_activate_synic(struct kvm_vcpu *vcpu, bool dont_zero_synic_pages)
 	 * not compatible with APICV, so request
 	 * to deactivate APICV permanently.
 	 */
-	kvm_request_apicv_update(vcpu->kvm, false, APICV_INHIBIT_REASON_HYPERV);
+	if (!kvm_hv_is_synic_autoeoi_deprecated(vcpu))
+		kvm_request_apicv_update(vcpu->kvm,
+					false, APICV_INHIBIT_REASON_HYPERV);
+
 	synic->active = true;
 	synic->dont_zero_synic_pages = dont_zero_synic_pages;
 	synic->control = HV_SYNIC_CONTROL_ENABLE;
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 105e785..0bb431f 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1263,6 +1263,9 @@ void kvm_apic_set_eoi_accelerated(struct kvm_vcpu *vcpu, int vector)
 
 	trace_kvm_eoi(apic, vector);
 
+	if (test_bit(vector, vcpu_to_synic(apic->vcpu)->vec_bitmap))
+		kvm_hv_synic_send_eoi(apic->vcpu, vector);
+
 	kvm_ioapic_send_eoi(apic, vector);
 	kvm_make_request(KVM_REQ_EVENT, apic->vcpu);
 }
-- 
1.8.3.1