Re: [Xen-devel] Question regarding SLAB corruption

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 9/7/07 08:38, "Lukas Hejtmanek" <xhejtman@xxxxxxxxxxx> wrote:

> On Sun, Jul 08, 2007 at 11:11:58AM +0100, Keir Fraser wrote:
>> DomU sets up its own DMAs. The BARs do not come into it (except that they
>> will indicate where device registers are, and that's how the DMA is
>> programmed).
> 
> One of maintainers of IB driver suggested a theory. What is the way that Xen
> allocates memory? Are there guarantees about allocation of physical contiguous
> memory? E.g., if I request alloc_pages(GPF_KERNEL, 6) - (256kB), are these
> pages physically contiguous? Or are these pages guest contiguous only?

Nope. To get contiguous pages on Xen you need to use pci_alloc_consistent,
or pci_map_single, or similar. Most drivers are okay with this, because you
are not supposed to program DMA without having got a dma_addr_t from Linux's
DMA API, and we hook into the DMA API to serve up contiguous regions (via
the swiotlb [ie. bounce buffers], if necessary).

 -- Keir


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