Re: [Xen-devel] Question regarding SLAB corruption

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 9/7/07 22:53, "Roland Dreier" <rdreier@xxxxxxxxx> wrote:

> Although I'm a little confused about the earlier parts of the story.
> Why was it necessary to force the use of swiotlb?  Shouldn't things
> work by default?

A swiotlb is a pre-allocated bounce-buffer region, so it has a memory cost
even if it's not actually used. Hence we do not create one by default for a
domU -- it has to be forced. Perhaps we could work out some way to detect
whether a swiotlb is likely to be needed, but our BUG_ON() messages are
pretty clear about why they are BUGging, and I considered that good enough.

> And is there any more intelligent way to give big chunks of system
> memory to a PCI device for exclusive use?

Perhaps dma_alloc_coherent/pci_alloc_consistent? These always return
machine-contiguous memory. I'm not sure if their use in this way would be an
abuse of the DMA API, though.

 -- Keir


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