RE: [Xen-devel] Full virtualization and I/O

["Puthiyaparambil, Aravindh" <aravindh.puthiyaparambil@xxxxxxxxxx>]

Mats,

> For fully virtualized mode (hardware supported virtual machine, such
as
> Finally, while I'm on the subject of fully virtualized mode: It is
> currently not possible to give a DMA-based device to a
fully-virtualized
> domain. The reason for this is that the guest OS will have been told
> that memory is from 0..256MB (say), and it's actual machine physical
> address is at 256MB..512MB. The OS is completely unaware of this
> "mismatch". So the OS will perform some operation to take a virtual
> address of some buffer (say a network packet) and make it into a
> "physical address", which will be an address in the range of 0..256MB.
> This will of course (at least) lead to the wrong data being
transmitted,
> as the address of the actual data is somewhere in the range
> 256MB..512MB. The only solution to this is to have an IOMMU, which can
> translate the guest's understanding of a physical address (0..256MB)
to
> a machine physical address (256..512MB).

I know that individual domains can be given direct access to individual
PCI devices.

http://www.cl.cam.ac.uk/research/srg/netos/xen/readmes/user/user.html#SE
CTION03230000000000000000

Is this not possible with HVM domains? Is it possible for HVM domains to
be a PCI frontend and receive a PCI device which is "hidden" from Dom0?
Or is this what paravirtualized drivers for HVM domains are doing?

Thanks,
Aravindh

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