[asterisk-users] New VirtualBox Beta Has PCI Pass-Through Support

[Steve Totaro]

I was going to ask about DMA but wasn't sure, what does the host report on
DMA and what does the guest OS report from cat /proc/dma?

Just curious if the host OS gives bogo-dma.

I am looking at timing issues which a think Free Switch has figured out
along with T38 a while ago.

I care slightly about using an actual TDM card since that can be handled by
Redfone or a USB device.

Thanks,
Steve Totaro

On Sun, Jul 10, 2011 at 4:11 AM, Tzafrir Cohen <tzafrir.cohen at xorcom.com>wrote:

> On Fri, Jul 08, 2011 at 07:28:39PM -0400, Doug Lytle wrote:
> > Can you say a Virtualized Asterisk with a PRI card!
> >
> > http://www.phoronix.com/scan.php?page=news_item&px=OTY0OQ
>
> I'm not sure this is relevant to your everyday PRI card.
>
> Simple pass-through of PCI is rather simple to implement. It has been
> implemented for quite some time in e.g. qemu, IIRC.
>
> But there's one important feature that is tricky to implement: DMA.
> DMA allows a PCI card to basically free access to the memory of the
> system, without the CPU getting in the middle. Emulating this with the
> host CPU in the middle will work, but is exepnsive. But the host does
> not want to give the guest free access to the host's memory.
>
> The solution: IOMMU: http://en.wikipedia.org/wiki/Iommu .
> The CPU of the system has a Memory Management Unit (MMU) that
> maps virtual address spaces to processes. Likewise we know prevent the
> IO card from seeing physical addresses. Rather, it sees virtual
> addresses mapped by the IOMMU. Just like the operating system maps
> addresses for processes, the hypervisor maps address ranger to IO cards.
>
> See also the link in that Phoronix article:
> http://www.ibm.com/developerworks/linux/library/l-pci-passthrough/
>
> I'm not well familiar with the relevant hardware, but I believe that not
> only not every CPU supports this, but many (most?) PCI cards don't
> support IOMMU.
>
> --
>               Tzafrir Cohen
> icq#16849755              jabber:tzafrir.cohen at xorcom.com
> +972-50-7952406           mailto:tzafrir.cohen at xorcom.com
> http://www.xorcom.com  iax:guest at local.xorcom.com/tzafrir
>
> --
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