static vm_fault_t kvm_vcpu_fault(struct vm_fault *vmf)
{
	struct kvm_vcpu *vcpu = vmf->vma->vm_file->private_data;
	struct page *page;

	if (vmf->pgoff == 0)
		page = virt_to_page(vcpu->run);
#ifdef CONFIG_X86
	else if (vmf->pgoff == KVM_PIO_PAGE_OFFSET)
		page = virt_to_page(vcpu->arch.pio_data);
#endif
#ifdef CONFIG_KVM_MMIO
	else if (vmf->pgoff == KVM_COALESCED_MMIO_PAGE_OFFSET)
		page = virt_to_page(vcpu->kvm->coalesced_mmio_ring);
#endif
	else
		return kvm_arch_vcpu_fault(vcpu, vmf);
	get_page(page);
	vmf->page = page;
	return 0;
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.