Re: ppc manual paging question

On Monday 22 October 2007 14:01:33, Benjamin Herrenschmidt wrote=EF=BC=9A

quoted

I'm porting an adeos nano kernel named xtratum (http://www.xtratum.org)
from x86 to ppc, I think I'm near the ending except the above problem.
xtratum is doing things like xen but it's much simpler (it's aimed for
realtime), it need provides memory space sperations for it's domains, so
I need manually paging. Each domain is loaded by a userspace program
(instead of the root domain as a kernel module), the loader will load t=

he

quoted

domain's (ELF staticly excutable) PT_LOAD section into memory, and then
raise a properly system call (passing the structurized loaded data as
arguments) to load the domain via load_domain_sys(), and at the last st=

ep

quoted

of loading the domain, xtratum will jump to the entry code of the new
domain(asm wrappered start() routine) and then everything should be fin=

e.

quoted

The problem now is as follow:

under my ppc (440GR/440EP) platform, start() is always at 0x100000a0, b=

ut

quoted

I guess there is something wrong with my mm code so after the domain is
loaded, the virt addres 0x100000a0 just point to garbage instead of the
right start() routine. So how can I setup paging properly so that the
virtual memory could be translated to proper data?

Are you aware that the 440 MMU doesn't actually know what a page table
is and doesn't load PTEs from memory ?

Sorry I didn't realized that. I've finished looking pem64b.pdf, but it's=20
almost nothing like in ppc 4xx/44x.

It's a software loaded TLB, you'll have to put translations in the TLB
yourself. You'll need to design your own data structures for that, tho
you can use a page table for tracking, like we do in linux, and then
have your own TLB miss handler to fill the TLB from that.

OK, Shall I look for the DataTLBError code in head.S? I realized that I've =
got=20
DataTLBError sometimes via BDI2000/kgdb (the fault address is within=20
DataTLBError), Shall I should also look for arch/ppc/mm/fault.c?

Your initial code probably need to bolt a TLB entry for the kernel
itself.

I don't understand this clearly, how can I do this?

Ben.

  Regards,
Wang


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OK, Shall I look for the DataTLBError code in head.S? I realized that I've got
DataTLBError sometimes via BDI2000/kgdb (the fault address is within
DataTLBError), Shall I should also look for arch/ppc/mm/fault.c?

if you end up in fault.c (via call to handle_page_fault) then I think you 
allready had an invalid access - you should not have ended there if the 
tlb entries would have been loaded properly from where ever XM put them
(not in any pgd that linux knows of) - no COW or lazy mechanism available
as the pgd of the domains are not handled in fault.c .

hofrat
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