Re: Xen #ifdef-age & x86 bus_space(9) implementation

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Wed, May 05, 2010 at 04:09:44PM -0500, David Young wrote:
> I don't understand some of the code that is conditionally compiled for
> XEN/!XEN.
> 
> Why don't both bus_space_map() and bus_space_alloc() do this?
> 
> #ifndef XEN
>         if (bpa >= IOM_BEGIN && (bpa + size) != 0 && (bpa + size) <= IOM_END) 
> {
>                 *bshp = (bus_space_handle_t)ISA_HOLE_VADDR(bpa);
>                 return(0);
>         }
> #endif  /* !XEN */
> 
> Only bus_space_map() contains that block.

I guess you used one of the bus_space_map() for something else
above.
I'm not sure, but I think the reason we're not running this for Xen
is that, for Xen the ISA memory hole is not automagically mapped
by locore.S at boot.

> 
> In x86_mem_add_mapping(), which both _alloc() and _map() call, there is
> a similar block:
> 
> #ifdef XEN
>         if (bpa >= IOM_BEGIN && (bpa + size) != 0 && (bpa + size) <= IOM_END) 
> {
>                 sva = (vaddr_t)ISA_HOLE_VADDR(pa);
>         } else
> #endif  /* XEN */
> 
> Should that be #ifndef XEN instead of #ifdef?

No, this is correct. On native x86 we never call this code for
the ISA hole. On Xen we do (because of the #ifndef XEN you asked about
above), and in this case we want to use the matching VA for the
physical ISA hole addresses, not something returned by our
allocator.

> 
> I would like for us to avoid this:
> 
>         for (va = sva; pa != endpa; pa += PAGE_SIZE, va += PAGE_SIZE) {
> #ifdef XEN
>                 pmap_kenter_ma(va, pa, VM_PROT_READ | VM_PROT_WRITE, 
> pmapflags);
> #else
>                 pmap_kenter_pa(va, pa, VM_PROT_READ | VM_PROT_WRITE, 
> pmapflags);
> #endif /* XEN */
>         }
> 
> Is there any reason not to add a weak alias pmap_kenter_ma ->
> pmap_kenter_pa, and to extract pmap_kenter_ma() into its own object that
> is linked into the Xen kernels, only?

that would work I guess (and for the pmap_extract* you ask in your
next message too).

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--