Re: pte_pagenr/MAP_NR deleted in pre6

["Stephen C. Tweedie" <sct@redhat.com>]

Hi,

On Wed, Aug 16, 2000 at 03:22:07PM -0700, Kanoj Sarcar wrote:

> > It's part of what is necessary if we want to push kiobufs into the
> > driver layers.  page_to_pfn is needed to for PAE36 support so that
> > PCI64 or dual-address-cycle drivers can handle physical addresses
> > longer than 32 bits long.
> 
> While we are on this topic, something like
> 
> #define page_to_phys(page) \
> 	((((page)-(page)->zone->zone_mem_map) << PAGE_SHIFT) \
> 	+ ((page)->zone->zone_start_paddr))
> 
> should work on all platforms on 2.4. (You might have to add in an
> unsigned long long somewhere in there for PAE36).

The long long is exactly what we need to avoid: PAE36 still has
pointers as 32-bit values.  Only ptes get the 64-bit treatment.

Adding a BUG() test to detect illegal accesses to >4GB pages on PAE36
would be fine.  If we have the appropriate bounce buffer support in
place in pci_dma or wherever suits it, then by the time a driver is
doing page_to_phys() it should already have created the appropriate
bounce buffers and so the BUG() test is fine. 

For DAC/PCI64 drivers, though, we need a separate macro like
page_to_pfn so that we can identify the physical address via a 32-bit
value.  The driver can then shift that into a 64-bit long long if it
wants to --- there's no need to introduce new 64-bit macros into the
mm just for this special case.

Cheers,
 Stephen
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