KVM: x86: deliver KVM IOAPIC scan request to target vCPUs

In IOAPIC fixed delivery mode instead of flushing the scan
requests to all vCPUs, we should only send the requests to
vCPUs specified within the destination field.

This patch introduces kvm_get_dest_vcpus_mask() API which
retrieves an array of target vCPUs by using
kvm_apic_map_get_dest_lapic() and then based on the
vcpus_idx, it sets the bit in a bitmap. However, if the above
fails kvm_get_dest_vcpus_mask() finds the target vCPUs by
traversing all available vCPUs. Followed by setting the
bits in the bitmap.

If we had different vCPUs in the previous request for the
same redirection table entry then bits corresponding to
these vCPUs are also set. This to done to keep
ioapic_handled_vectors synchronized.

This bitmap is then eventually passed on to
kvm_make_vcpus_request_mask() to generate a masked request
only for the target vCPUs.

This would enable us to reduce the latency overhead on isolated
vCPUs caused by the IPI to process due to KVM_REQ_IOAPIC_SCAN.

Suggested-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 60fb21fe7f42..452cedd6382b 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1122,6 +1122,50 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
 	return result;
 }
 
+/*
+ * This routine identifies the destination vcpus mask meant to receive the
+ * IOAPIC interrupts. It either uses kvm_apic_map_get_dest_lapic() to find
+ * out the destination vcpus array and set the bitmap or it traverses to
+ * each available vcpu to identify the same.
+ */
+void kvm_bitmap_or_dest_vcpus(struct kvm *kvm, struct kvm_lapic_irq *irq,
+			      unsigned long *vcpu_bitmap)
+{
+	struct kvm_lapic **dest_vcpu = NULL;
+	struct kvm_lapic *src = NULL;
+	struct kvm_apic_map *map;
+	struct kvm_vcpu *vcpu;
+	unsigned long bitmap;
+	int i, vcpu_idx;
+	bool ret;
+
+	rcu_read_lock();
+	map = rcu_dereference(kvm->arch.apic_map);
+
+	ret = kvm_apic_map_get_dest_lapic(kvm, &src, irq, map, &dest_vcpu,
+					  &bitmap);
+	if (ret) {
+		for_each_set_bit(i, &bitmap, 16) {
+			if (!dest_vcpu[i])
+				continue;
+			vcpu_idx = dest_vcpu[i]->vcpu->vcpu_idx;
+			__set_bit(vcpu_idx, vcpu_bitmap);
+		}
+	} else {
+		kvm_for_each_vcpu(i, vcpu, kvm) {
+			if (!kvm_apic_present(vcpu))
+				continue;
+			if (!kvm_apic_match_dest(vcpu, NULL,
+						 irq->delivery_mode,
+						 irq->dest_id,
+						 irq->dest_mode))
+				continue;
+			__set_bit(i, vcpu_bitmap);
+		}
+	}
+	rcu_read_unlock();
+}
+
 int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2)
 {
 	return vcpu1->arch.apic_arb_prio - vcpu2->arch.apic_arb_prio;