RE: [Xen-devel] Shared memory and event channel

[<djmagee@xxxxxxxxxxxx>]

What is the data you’re trying to access in the device registers?  If it’s statistics, which you gave as an example, then why would a domain want to read statistics for a card that shared by many other guests, of which it has no knowledge?  In fact, I’m struggling to think of any situation where data applicable to the physical card that’s carrying packets for every guest on the box could be useable by one single guest.

 

Can’t you just write a daemon in dom0 that reads the data you’re interested in and makes it available to the domUs via a simple network service?

 

From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Ritu kaur
Sent: Tuesday, February 23, 2010 10:53 AM
To: Ian Campbell
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Daniel Stodden; Konrad Rzeszutek Wilk
Subject: Re: [Xen-devel] Shared memory and event channel

 

Hi Ian,

Thanks for your inputs, I skimmed through Intel 82576 SR-IOV document and it looks like it needs hardware support and I don't think our hardware has it(will double check with our team). I believe currently there is no good solution other than using pci passthrough(with a single domU access). I just want to bring one thing and I hope it was not missed out from my earlier email i.e

"The NIC registers are memory mapped, can I take "machine memory address space(which is in dom0)" and remap it to domU's such that I can get multiple domU access. "

The above soln is just a thought, not sure it's feasible.

Thanks

On Tue, Feb 23, 2010 at 7:42 AM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:

On Tue, 2010-02-23 at 14:47 +0000, Konrad Rzeszutek Wilk wrote:
> On Tue, Feb 23, 2010 at 09:38:26AM +0000, Ian Campbell wrote:
> > On Mon, 2010-02-22 at 22:16 +0000, Ritu kaur wrote:
> > >
> > > All I need to  is access NIC registers via domU's(network controller
> > > will still be working normally). Using PCI passthrough solves the
> > > problem for a domU, however, it doesn't solve when multiple domU's
> > > wanting to read NIC registers(ex. statistics).
> >
> > Direct access to hardware registers and availability of the device to
> > multiple guest domains are mutually exclusive configurations under Xen
> > (in the absence of additional technologies such as SR-IOV).
> >
> > The paravirtual front and back devices contain no hardware specific
> > functionality, in this configuration all hardware specific knowledge is
> > contained in the driver in domain 0. Guests use regular L2 or L3
> > mechanisms such as bridging, NAT or routing to obtain a path to the
> > physical hardware but they are never aware of that physical hardware.
> >
> > PCI passthrough allows a guest direct access to a PCI device but this is
> > obviously incompatible with access from multiple guests (again, unless
> > you have SR-IOV or something similar)
>
> What if the netback was set be able to work in guest mode? This way you
> could export it out to the guests?

Like a driver domain model? That would work (I think) but is still not
the same as having multiple domain's with access to the physical
registers. netback in a guest works in exactly the same as how it works
for domain 0.

Ian.

 

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