Ensure that if userspace supplies insufficient data to PTRACE_SETREGSET to fill all the registers, the thread's old registers are preserved. convert_vx_to_fp() is adapted to handle only a specified number of registers rather than unconditionally handling all of them: other callers of this function are adapted appropriately. Based on an initial patch by Dave Martin. Cc: stable@vger.kernel.org Reported-by: Dave Martin <Dave.Martin@arm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>