PAE & hypercall interfaces

PAE & hypercall interfaces

[Gerd Knorr]

  Hi folks,

As mentioned already in the pae patch mail, the xen hypercall
interfaces needs some changes.  The affected calls (hope I
didn't miss one) are:

 * do_mmuext_op
 * do_update_va_mapping & friends

The problem is that in PAE mode the page table entries are
64bit-sized instead of 32bit, and the current hypercall
interfaces allow to pass 32bit values only.

Current state is that the PAE code simply passes the lower
32 bits only, which will work fine as long as nobody attempts
to address memory above 4GB.  That obviously isn't an option,
the whole point of the PAE attempts is to use the memory above
4GB ;)

The options we have are:

  (1) make page table entrys 64bit wide everythere.
  (2) make page table entrys 64bit wide in PAE mode only.
  (3) pass two values: 32bit page frame number & flags.
  (4) others?

I'd prefeare option (1), option (3) is reasonable as well I
think.  I don't think (2) is a good idea, that will cause some
very nasty problems in case we'll try to allow non-PAE guests in
PAE mode.

Comments?

  Gerd

-- 
-mm seems unusually stable at present.
	-- akpm about 2.6.12-rc3-mm3

Re: PAE & hypercall interfaces

[Keir Fraser]

On 18 May 2005, at 20:23, Gerd Knorr wrote:

>   (1) make page table entrys 64bit wide everythere.
>   (2) make page table entrys 64bit wide in PAE mode only.
>   (3) pass two values: 32bit page frame number & flags.
>   (4) others?
>
> I'd prefeare option (1), option (3) is reasonable as well I
> think.  I don't think (2) is a good idea, that will cause some
> very nasty problems in case we'll try to allow non-PAE guests in
> PAE mode.
>
> Comments?

I like option 3.

  -- Keir

RE: PAE & hypercall interfaces

[Ian Pratt]

 

> On 18 May 2005, at 20:23, Gerd Knorr wrote:
> 
> >   (1) make page table entrys 64bit wide everythere.
> >   (2) make page table entrys 64bit wide in PAE mode only.
> >   (3) pass two values: 32bit page frame number & flags.
> >   (4) others?
> >
> > I'd prefeare option (1), option (3) is reasonable as well I 
> think.  I 
> > don't think (2) is a good idea, that will cause some very nasty 
> > problems in case we'll try to allow non-PAE guests in PAE mode.
> >
> > Comments?
> 
> I like option 3.

As do I, cooking down the NX bit.

Ian