Using arch/x86_64/pci-dma in x86_64 Xen

Using arch/x86_64/pci-dma in x86_64 Xen

[Langsdorf, Mark]

The current implementation of pci-dma in x86_64 Xen
Linux is to use the i386 implementation.  I don't
believe this is sustainable in the long term, as
x86_64 Xen is going to need more DMA solutions than
just SWIOTLB and plain hardware as various IOMMU 
implementations arrive.  

The mainstream kernel has a clean abstraction layer
with the dma_ops that should be portable to Xen dom0
and domU.  I've started implementing this in a
pci-dma-xen for x86_64 Xen Linux.  Am I stepping on 
anyone's toes or is there anyone I should be 
co-ordinating this with?

-Mark Langsdorf
AMD, Inc.

Re: Using arch/x86_64/pci-dma in x86_64 Xen

[Jon Mason]

On Thu, May 04, 2006 at 09:57:35AM -0500, Langsdorf, Mark wrote:
> The current implementation of pci-dma in x86_64 Xen
> Linux is to use the i386 implementation.  I don't
> believe this is sustainable in the long term, as
> x86_64 Xen is going to need more DMA solutions than
> just SWIOTLB and plain hardware as various IOMMU 
> implementations arrive.  
> 
> The mainstream kernel has a clean abstraction layer
> with the dma_ops that should be portable to Xen dom0
> and domU.  I've started implementing this in a
> pci-dma-xen for x86_64 Xen Linux.  Am I stepping on 
> anyone's toes or is there anyone I should be 
> co-ordinating this with?

This is long overdue.  Thanks for starting the work.  

Muli and I have been peripherally looking at this, but have not done any
work on it yet.  Please keep us in the loop, and let us know if you need
any help :)

Thanks,
Jon

> 
> -Mark Langsdorf
> AMD, Inc.
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

Re: Using arch/x86_64/pci-dma in x86_64 Xen

[Muli Ben-Yehuda]

On Thu, May 04, 2006 at 09:57:35AM -0500, Langsdorf, Mark wrote:

> The current implementation of pci-dma in x86_64 Xen
> Linux is to use the i386 implementation.  I don't
> believe this is sustainable in the long term, as
> x86_64 Xen is going to need more DMA solutions than
> just SWIOTLB and plain hardware as various IOMMU 
> implementations arrive.

100% agreed.

> The mainstream kernel has a clean abstraction layer
> with the dma_ops that should be portable to Xen dom0
> and domU.  I've started implementing this in a
> pci-dma-xen for x86_64 Xen Linux.  Am I stepping on 
> anyone's toes or is there anyone I should be 
> co-ordinating this with?

Please keep Jon and me in the loop, we added the dma_ops to the main
kernel for the Calgary IOMMU but haven't got around to porting the
various Xen dma ops to it.

Also, I believe Christian had some thoughts about the direction going
forward for the Xen specific dma ops?

Cheers,
Muli

Re: Using arch/x86_64/pci-dma in x86_64 Xen

[Christian Limpach]

On 5/7/06, Muli Ben-Yehuda <muli@il.ibm.com> wrote:
> On Thu, May 04, 2006 at 09:57:35AM -0500, Langsdorf, Mark wrote:
>
> > The current implementation of pci-dma in x86_64 Xen
> > Linux is to use the i386 implementation.  I don't
> > believe this is sustainable in the long term, as
> > x86_64 Xen is going to need more DMA solutions than
> > just SWIOTLB and plain hardware as various IOMMU
> > implementations arrive.
>
> 100% agreed.
>
> > The mainstream kernel has a clean abstraction layer
> > with the dma_ops that should be portable to Xen dom0
> > and domU.  I've started implementing this in a
> > pci-dma-xen for x86_64 Xen Linux.  Am I stepping on
> > anyone's toes or is there anyone I should be
> > co-ordinating this with?
>
> Please keep Jon and me in the loop, we added the dma_ops to the main
> kernel for the Calgary IOMMU but haven't got around to porting the
> various Xen dma ops to it.
>
> Also, I believe Christian had some thoughts about the direction going
> forward for the Xen specific dma ops?

I think that using the dma_ops abstraction layer on x86_64 is
definitely the way to go.  It's just not clear how the Xen specific
dma ops should be implemented in the end, whether having a common
implementation is worthwhile considering that it will require glue
code to make it fit with the different interfaces.

     christian

RE: Using arch/x86_64/pci-dma in x86_64 Xen

[Langsdorf, Mark]

> > > The mainstream kernel has a clean abstraction layer
> > > with the dma_ops that should be portable to Xen dom0
> > > and domU.  I've started implementing this in a
> > > pci-dma-xen for x86_64 Xen Linux.  Am I stepping on 
> > > anyone's toes or 
> > > is there anyone I should be co-ordinating this with?
> 
> I think that using the dma_ops abstraction layer on x86_64 is 
> definitely the way to go.  It's just not clear how the Xen 
> specific dma ops should be implemented in the end, whether 
> having a common implementation is worthwhile considering that 
> it will require glue code to make it fit with the different 
> interfaces.

I don't think there's enough differences between the bare
metal dma ops and the Xen dma ops to justify a common
implementation.  Also, the common implementation implies
that each IOMMU interface needs to have some knowledge of
the other interfaces, and I don't think that's sustainable
long term.

-Mark Langsdorf
AMD, Inc.