copy_from_user user space address mapping in the kernel page table.

Hi, In the copy_from_user when the user passes the virtual address is the address mapped in the kernel page tables? In the function there is a source is a user virtual address(<3GB) and the destination is the kernel virtual address(3GB - 4GB) and for the MMU to access the physical page frame when in kernel space operating in behalf of the process context there should be a mapping of the virtual address to the page frame, correct? I am assuming the implementation would be to take the virtual address and walk the page table to get to the physical page frame and map the physical page frame in the kernel page table (i.e. swapper_pgd). Is this correct? If not what would be the mechanism? Thanks, Gautam.