static int kvm_read_guest_virt_helper(gva_t addr, void *val, unsigned int bytes,
				      struct kvm_vcpu *vcpu, u32 access,
				      struct x86_exception *exception)
{
	void *data = val;
	int r = X86EMUL_CONTINUE;

	while (bytes) {
		gpa_t gpa = vcpu->arch.walk_mmu->gva_to_gpa(vcpu, addr, access,
							    exception);
		unsigned offset = addr & (PAGE_SIZE-1);
		unsigned toread = min(bytes, (unsigned)PAGE_SIZE - offset);
		int ret;

		if (gpa == UNMAPPED_GVA)
			return X86EMUL_PROPAGATE_FAULT;
		ret = kvm_read_guest_page(vcpu->kvm, gpa >> PAGE_SHIFT, data,
					  offset, toread);
		if (ret < 0) {
			r = X86EMUL_IO_NEEDED;
			goto out;
		}

		bytes -= toread;
		data += toread;
		addr += toread;
	}
out:
	return r;
}

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.