Re: [Xen-devel] xen kernel 2.6.18 bug with a d-link DFE 580TX - pci hide

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 26/10/08 19:17, "Michael Kapp" <tquarkk@xxxxxxxxxx> wrote:

>> The network card is only capable of 32-bit DMA. So for addresses above 4GB a
>> bounce buffer is required (DMA to/from bounce buffer; then copy to/from
>> proper high-memory buffer using host CPU). The swiotlb is basically a
>> pre-allocated bounce-buffer area. Because it is pre-allocated it is a waste
>> of memory if it isn't used and, since domUs do not normally perform real
>> physical I/O directly, we therefore by default only create a swiotlb for
>> dom0. You then have to override on the cmdline if this default doesn't
>> actually work (as in this case).
> 
> ...and why is it not possible (from the dom0 point of view) to detect
> this behaviour while starting the domU, reading it's conf and stop the
> boot process with a warning?

IOMMU_BUG_ON() is supposed to printk a suitable warnign before actually
crashing. Not sure why that didn't work for you.

 -- Keir



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