wasting time on page fault

[Mikulas Patocka]

Hi.

arch/i386/kernel/entry.S
        xchgl %eax, ORIG_EAX(%esp)      # orig_eax (get the error code. )
        movl %esp,%edx
        xchgl %ecx, ES(%esp)            # get the address and save es.
        pushl %eax                      # push the error code

xchg with memory operand has implicit lock prefix and is slooooooow. It is
really bad idea to have it in page fault handler.

Mikulas