Re: [PATCH 16 of 55] xen64: add extra pv_mmu_ops

[Jeremy Fitzhardinge]

Mark McLoughlin wrote:
> Hey Jeremy,
>
> On Tue, 2008-07-08 at 15:06 -0700, Jeremy Fitzhardinge wrote:
>   
> > We need extra pv_mmu_ops for 64-bit, to deal with the extra level of
> > pagetable.
> >
> > Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
> > ---
> >  arch/x86/xen/enlighten.c   |   33 +++++++++++++++++++++++++++-
> >  arch/x86/xen/mmu.c         |   51 +++++++++++++++++++++++++++++++++++++++++++-
> >  arch/x86/xen/mmu.h         |   15 +++++++++++-
> >  include/asm-x86/xen/page.h |    4 +++
> >  4 files changed, 99 insertions(+), 4 deletions(-)
> >     
> ...
>   
> > diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> > --- a/arch/x86/xen/mmu.c
> > +++ b/arch/x86/xen/mmu.c
> > @@ -438,14 +438,19 @@
> >  
> >  void xen_set_pte(pte_t *ptep, pte_t pte)
> >  {
> > +#ifdef CONFIG_X86_PAE
> >  	ptep->pte_high = pte.pte_high;
> >  	smp_wmb();
> >  	ptep->pte_low = pte.pte_low;
> > +#else
> > +	*ptep = pte;
> > +#endif
> >  }
> >     
>
> You've dropped non-PAE support already, right? Any reason to use the
> X86_PAE macro instead of X86_32?
>   

It's a fine difference, but the specific thing I'm testing for is 
actually PAE vs 64-bit (or even more specifically "can I update a whole 
pte atomically?").  Testing for X86_32 is equivalent in the absence of 
non-PAE 32-bit, but not quite as correct.  The other way I could do it 
is as I have elsewhere:

	if (sizeof(pte_t) > sizeof(long)) {
		ptep->pte_high = pte.pte_high;
		smp_wmb();
		ptep->pte_low = pte.pte_low;
	} else
		*ptep = pte;

But there are other places where it tests for this using PAE (and even 
whole pvops which are only defined in the PAE case).

You'll notice other places where I test for PAGETABLE_LEVELS == 3 where 
the code  is generally handling 3-level pagetables, and others where I 
test for PAE where it's something specific to PAE.

   J
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