[RFC PATCH v3 17/19] KVM: x86: nSVM: implement nested AVIC doorbell emulation

[Maxim Levitsky <mlevitsk@redhat.com>]

This patch implements the doorbell msr emulation
for nested AVIC.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 arch/x86/kvm/svm/avic.c | 49 +++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.c  |  2 ++
 arch/x86/kvm/svm/svm.h  |  1 +
 3 files changed, 52 insertions(+)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index e8c53fd77f0b1..149df26e17462 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -1165,6 +1165,55 @@ unsigned long avic_vcpu_get_apicv_inhibit_reasons(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
+int avic_emulate_doorbell_write(struct kvm_vcpu *vcpu, u64 data)
+{
+	int source_l1_apicid = vcpu->vcpu_id;
+	int target_l1_apicid = data & AVIC_DOORBELL_PHYSICAL_ID_MASK;
+	bool target_running, target_nested;
+	struct kvm_vcpu *target;
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	if (!svm->avic_enabled || (data & ~AVIC_DOORBELL_PHYSICAL_ID_MASK))
+		return 1;
+
+	target = avic_vcpu_by_l1_apicid(vcpu->kvm, target_l1_apicid);
+	if (!target)
+		/* Guest bug: targeting invalid APIC ID. */
+		return 0;
+
+	target_running = READ_ONCE(target->mode) == IN_GUEST_MODE;
+	target_nested = is_guest_mode(target);
+
+	trace_kvm_avic_nested_doorbell(source_l1_apicid, target_l1_apicid,
+				       target_nested, target_running);
+
+	/*
+	 * Target is not in the nested mode, thus the doorbell doesn't affect it.
+	 * If it just became nested after is_guest_mode was checked,
+	 * it means that it just processed AVIC state and KVM doesn't need
+	 * to send it another doorbell.
+	 */
+	if (!target_nested)
+		return 0;
+
+	/*
+	 * If the target vCPU is in guest mode, kick the real doorbell.
+	 * Otherwise KVM needs to try to wake it up if it was sleeping.
+	 *
+	 * If the target is not longer in guest mode (just exited it),
+	 * it will either halt and before that it will notice pending IRR
+	 * bits, and cancel halting, or it will enter the guest mode again,
+	 * and notice the IRR bits as well.
+	 */
+	if (target_running)
+		wrmsr(MSR_AMD64_SVM_AVIC_DOORBELL,
+		      kvm_cpu_get_apicid(READ_ONCE(target->cpu)), 0);
+	else
+		kvm_vcpu_wake_up(target);
+
+	return 0;
+}
+
 static u32 *avic_get_logical_id_entry(struct kvm_vcpu *vcpu, u32 ldr, bool flat)
 {
 	struct kvm_svm *kvm_svm = to_kvm_svm(vcpu->kvm);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index d96a73931d1e5..b31bab832360e 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2772,6 +2772,8 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 	u32 ecx = msr->index;
 	u64 data = msr->data;
 	switch (ecx) {
+	case MSR_AMD64_SVM_AVIC_DOORBELL:
+		return avic_emulate_doorbell_write(vcpu, data);
 	case MSR_AMD64_TSC_RATIO:
 
 		if (!svm->tsc_scaling_enabled) {
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 93fd9d6f5fd85..14e2c5c451cad 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -714,6 +714,7 @@ unsigned long avic_vcpu_get_apicv_inhibit_reasons(struct kvm_vcpu *vcpu);
 void avic_reload_apic_pages(struct kvm_vcpu *vcpu);
 void avic_free_nested(struct kvm_vcpu *vcpu);
 bool avic_nested_has_interrupt(struct kvm_vcpu *vcpu);
+int avic_emulate_doorbell_write(struct kvm_vcpu *vcpu, u64 data);
 
 struct avic_physid_table *
 avic_physid_shadow_table_get(struct kvm_vcpu *vcpu, gfn_t gfn);
-- 
2.26.3