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

Maxim Levitsky
2022-04-27T20:08:40Z

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