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

[Michael Kapp <tquarkk@xxxxxxxxxx>]

Keir Fraser wrote:
>> Can you tell me what this parameter is doing in detail, or where i can
>> find docs about it?
> 
> 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?

Michael

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