RE: [Xen-users] PCI passtrough in HVM Domain ?

[Sven Oehme <oehmes@xxxxxxxxxx>]

ok understood and make sense to me :-)

Virtual PCI is supported today ( at
least it tells me in the log, that it has attached the device to the guest)
but it still doesn't show up in the guest vm .

Sven

"Petersson, Mats" <Mats.Petersson@xxxxxxx>

05/19/2006 02:22 PM

To	Sven Oehme/Germany/IBM@IBMDE, xen-users@xxxxxxxxxxxxxxxxxxx
cc
Subject	RE: [Xen-users] PCI passtrough in HVM Domain ?

PCI passthrough isn't supported
for HVM guests yet. I don't know why - it shouldn't be too difficult to
achieve, I would have thought, but on the other hand, for 90% of devices,
it probably doesn't make much sense to just pass them on, since those 90%
use direct memory accesses for the data transfers to/from the device, and
thus you'd end up shipping out the wrong data - which at best means that
the device just won't work, or at worst means that some data from another
domain gets sent out to the public to see - the latter is worse becaue
you wouldn't know it until you find that your bank-account has been emptied,
because you sent all the details off onto the WWW and someone picked it
up... ;-)
 
The reason for this is that the
HVM guest domain THINKS that memory starts at address zero (or thereabouts)
and goes to whatever size we've assigned it. But in reality, the memory
used by the HVM guest is living at, for example, 256-512MB. So when the
network card is told to transmit memory from address 123456, it should
really transmit what's at 256MB + 123456, not actual address 123456. Since
the OS and it's drivers are completely unaware about this fact, they can't
really fix it... 
 
There are two solutions to this
problem:
1. Use an IOMMU - unfortunately,
there's none available for common x86 hardware today [IBM has one, which
is used for large MP systems, I think - not sure if it's x86 or PowerPC
based]. 
2. Use para-virtualized drivers,
so the driver is capable of figuring out that the ACTUAL physical address
of the data to be DMA'd is different from the OS's idea of the address.

 
--
Mats

---

From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Sven
Oehme
Sent: 18 May 2006 22:32
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] PCI passtrough in HVM Domain ?


Hi , 

can i pass a PCI device to a HVM domain ? 
i tried Virtual_PCI and Pass trough as PCI_Backends. 
in the boot log i see that he hides the device and when i start the domain
it tells me that he assigned it now to the domain 
but in both ways the Adapter doesn't appears in the Windows System that
runs in the HVM domain. 

any ideas ? 

Sven
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