1. A method of cloning data in a memory for a source virtual machine (VM) and at least one cloned virtual machine, wherein the source virtual machine and the at least one cloned virtual machine are system virtual machines, wherein a mapping relationship between a guest physical address from the source VM or the at least one cloned VM and a host physical address of the memory is defined by a plurality of page tables configured in a plurality of hierarchical levels, the method comprising: copying metadata of the page tables in a highest level or higher levels of the plurality of hierarchical levels of the source VM to the at least one cloned virtual machine; setting the metadata of the page tables in the highest level or the higher levels of the plurality of hierarchical levels of the source VM invalid; copying remaining metadata of the page tables in levels other than the metadata of the page tables in the highest level or the higher levels of the plurality of hierarchical levels of the source VM to the at least one cloned virtual machine in response to an access operation; accessing data stored in corresponding address of the memory according to the copied metadata of the page tables in the highest level or higher levels and the copied metadata of the page tables in the levels other than the metadata of the page tables in the highest level or the higher levels; and writing data to the corresponding address of the memory by copy-on-write (COW) technique for isolated protection and/or independent execution between the source VM and the at least one cloned VM, wherein before writing data to the corresponding address of the memory by copy-on-write (COW) technique, a lowest level of the copied metadata of the page tables in the levels other than the metadata of the page tables in the highest level or the higher levels are set to be read only.