I should add a clarification regarding the per-cpu info.  I think the
    distinction should be as a separate PML4 entry and not a PDP entry.  This
    way the kernel can have a single PDP/PD hierarchy that is shared across
    all cpus.
 
    The per-cpu magic can be statically hardwired for each cpu via a PML4
    entry and maybe a few other pages (per-cpu) creating a PDP/PD
    hierarchy.   There are two ways to do it.
 
    (1) We can map a page containing the address of the per-cpu globaldata
        structure and use %fs in the trap code:
 
        movq	$SOME_FIXED_CONSTANT_ADDRESS,%fs
 
    (2) We can map the actual per-cpu globaldata to a fixed address and access
        it directly.

    Either way will work.  I will note that the system code expects 'mycpu'
    to be a variable kernel space address representing the location of the
    globaldata structure in kernel space and it will get confusde if
    'mycpu' returns the same fixed address on every cpu.  So the %fs method
    may be the best way to go so we don't have to run through all the system
    code changing the expectations for 'mycpu'.

							-Matt

Hi Matt,

just to make sure: when you talking about the globaldata, it is
per-cpu, not globaldata for the whole system, am I right?

is the CPU_prvspace in machine/globaldata.h the array to keep the
per-cpu globaldata?

More questions coming :)

yyh

Hi Matt,

lots of things hang me around by the department open house.
thanks for your suggestions. some of them i am not fully understand,
but prefer to hold my questions until i see that it starting to
trouble me :).

will start with the simple solution first and then move on to
something complicated.

yyh

just for curious: what is recursive pml4 mapping, found from freebsd pmap.h

also, freebsd only have a page of PML4 entries, about 4K/64=64
entries, not all 512 (2**9).

You don't have to play such games on AMD64 -- the swapgs instruction is
normally used by traps and system calls to load a well-defined address
base for that. Note that gs is expected to be used for, but that is a
minor detail.

Joerg