Re: [Xen-devel] Question regarding SLAB corruption

[Lukas Hejtmanek <xhejtman@xxxxxxxxxxx>]

On Mon, Jul 09, 2007 at 02:53:53PM -0700, Roland Dreier wrote:
>  > Great! With this "fix", it turns on interface ib0. Many thanks to all!
> 
> in domU?  That is cool.

Yes! I'm able to ping another machine over the IB from DomU. In Dom0, the
driver works as well. (It stoped to work after swiotlb patches to the Xen.)

> Anyway I think the real fix is to switch to dma_sync_single_range in
> mthca along with Keir's fixes to swiotlb.

OK, I see. I would be happy to test any further patches if you are about to do
them.

> 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?

I guess it's because swiotlb is ON by default in Dom0. So forcing it also in
DomU makes it equivalent to Dom0. And because both domains are virtual, i.e.,
the domains do not see *real* physical memory then standard memory mapping
routines do not work. It's my guess.
 
> And is there any more intelligent way to give big chunks of system
> memory to a PCI device for exclusive use?

Maybe some support in Xen - a syscall that is able to map contiguous ares but
also in this case, we have problem migration and reporting physical addresses
to the PCI device. It's similar to FTP and NAT problem. NAT basically
virtualizes network but the FTP needs to pass data IP thus hooks in NAT are 
needed. We would need similar hooks here or to deny sending 'virtual physical'
address to the devices.

-- 
Lukáš Hejtmánek

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