KVM: Convert kvm_for_each_vcpu() to using xa_for_each_range()

Now that the vcpu array is backed by an xarray, use the optimised
iterator that matches the underlying data structure.
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Message-Id: <20211116160403.4074052-8-maz@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/linux/kvm_host.h

@@ -706,10 +706,8 @@ static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i)
 }
 
 #define kvm_for_each_vcpu(idx, vcpup, kvm)		   \
-	for (idx = 0; \
-	     idx < atomic_read(&kvm->online_vcpus) && \
-	     (vcpup = kvm_get_vcpu(kvm, idx)) != NULL; \
-	     idx++)
+	xa_for_each_range(&kvm->vcpu_array, idx, vcpup, 0, \
+			  (atomic_read(&kvm->online_vcpus) - 1))
 
 static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)
 {