pmap of amd64
noah.yan at gmail.com
Tue Oct 16 14:52:17 PDT 2007
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).
On 10/16/07, Yonghong Yan <noah.yan at gmail.com> wrote:
> 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.
> On 10/12/07, Matthew Dillon <dillon at apollo.backplane.com> wrote:
> > 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
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