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Re: [Xen-devel] Failure to get memory for GATT table, again

On Tue, Feb 01, 2005 at 11:18:07PM +0000, Ian Pratt wrote:
> > > The AGP aperture needs a set of machine contiguous pages, whereas
> > > get_free_pages will only give you pseudo-physical contiguous.
> > > 
> > > Drivers are supposed to use the former (for reasons of ensuring
> > > DMA coherence) , but the agp drivers seem particularly shoddy,
> > > probably because they've only ever been used on x86.
> > 
> > Hmm but it seems that dev->dma_mem is never set for the device, causing a 
> > fallback to
> > __get_free_pages(). Should the driver have set this?
> dma_alloc_coherent allocates some pages, then calls
> xen_contig_memory which swaps them for machine contiguous ones.
> You should be able to call ioremap_nocache on the virt_to_bus'ed
> address you get back from xen_contig_memory.

Apparently this is where things go wrong; the pages I get from __get_free_pages
seem to always be a the top of dom0 mem (probably because order is 6), and when
converted with virt_to_bus I get an mfn which Xen thinks is not owned by dom0.

> Ian


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