virtual memmap and page_address

virtual memmap and page_address

[Jesse Barnes]

I've been messing around with some of the drm drivers lately, and in some 
cases they'll call pci_map_single on an address returned from page_address().  
When virtual memmaps are enabled, page_address will return a region 5 
pointer.  It looks like all of the ia64 iommu code (swiotlb, sba_iommu and 
sn2's pci_dma) assume that the address passed in is an identity mapped 
address since they use __pa to get the physical address.  This is fast, but 
also incorrect when the routines are handed a region 5 address.  So we either 
have to fix our iommu mapping routines or change some other assumptions 
(either about what page_address should return or what __va in general means 
for example).  Turning on WANT_PAGE_VIRTUAL and populating page->virtual with 
an identity mapped address is another option, probably less expensive than 
switching to ia64_tpa in the mapping routines.

Comments?

Thanks,
Jesse

RE: virtual memmap and page_address

[Luck, Tony]

>When virtual memmaps are enabled, page_address will return a region 5 
>pointer.

Are you sure?  It looks to me that without WANT_PAGE_VIRTUAL that
we end up in lowmem_page_address(), which just gives us:

  __va(page_to_pfn(page) << PAGE_SHIFT)

which has got to be a region 7 address.

What's the code path that you are looking at that can return a
region 5 address?

-Tony

Re: virtual memmap and page_address

[David Mosberger]

>>>>> On Wed, 15 Dec 2004 09:53:32 -0800, Jesse Barnes <jbarnes@engr.sgi.com> said:

  Jesse> I've been messing around with some of the drm drivers lately,
  Jesse> and in some cases they'll call pci_map_single on an address
  Jesse> returned from page_address().  When virtual memmaps are
  Jesse> enabled, page_address will return a region 5 pointer.

Huh?  The page _descriptor_ is in region 5, but surely not page_address()?

	--david

Re: virtual memmap and page_address

[Jesse Barnes]

On Wednesday, December 15, 2004 9:53 am, Jesse Barnes wrote:
> I've been messing around with some of the drm drivers lately, and in some
> cases they'll call pci_map_single on an address returned from
> page_address(). When virtual memmaps are enabled, page_address will return
> a region 5 pointer.  It looks like all of the ia64 iommu code (swiotlb,
> sba_iommu and sn2's pci_dma) assume that the address passed in is an
> identity mapped address since they use __pa to get the physical address. 
> This is fast, but also incorrect when the routines are handed a region 5
> address.  So we either have to fix our iommu mapping routines or change
> some other assumptions (either about what page_address should return or
> what __va in general means for example).  Turning on WANT_PAGE_VIRTUAL and
> populating page->virtual with an identity mapped address is another option,
> probably less expensive than switching to ia64_tpa in the mapping routines.

Nevermind, obviously I haven't had enough coffee this morning.  page_address 
correctly returns an identity mapped address so my problem lies elsewhere.