Re: [Xen-devel] PCI pass-through

["David Stone" <unclestoner@xxxxxxxxx>]

Thanks for your responses Mark and Keir, that makes sense to me.

Dave

On Nov 7, 2007 2:31 AM, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:
> They're not really equal -- dom0 manages the platform (IRQ routing, ACPI
> OSPM stuff, etc.). This type of thing is hard to decentralise, so dom0
> continues to manage basic setup of PCI devices, some of which is triggered
> by accesses to PCI config space by domUs, via pcifront/pciback. However,
> device-specific management is done by the domU itself. dom0 is not involved
> in any data paths.
>
>  -- Keir
>
>
> On 6/11/07 20:27, "David Stone" <unclestoner@xxxxxxxxx> wrote:
>
> > Hi guys, I'm trying to understand the architecture of the PCI
> > pass-through functionality on Xen.  Just to be clear, I'm (for now)
> > trying to understand what's happening when a PCI device is "hidden"
> > from (PV) Dom0 and exposed to a PV DomU.
> >
> > I was originally assuming that as long as Dom0 was told not to touch a
> > particular PCI device, then DomU could be granted direct access do it,
> > and operations on that device would go through its normal drivers on
> > DomU, and the DomU kernel with no involvement whatsoever from Dom0.
> > The model in my mind is that since Dom0 and DomU are equally
> > paravirtualized, there is no reason that DomU couldn't be given the
> > same exact mechanism for access to the PCI device as Dom0 is normally
> > given...it's just a matter of configuration.
> >
> > But in looking in how to configure this, I see there are pciback and
> > pcifront drivers...just like netback and netfront.  I thought maybe
> > pciback's sole purpose was to hide specified PCI devices from Dom0,
> > but there is quite a bit of code in the source for pciback.  Also in
> > pcifront I see xenbus.c, suggesting it communicates with its back-end
> > counterpart just like netfront or blkfront.
> >
> > So, when one grant's "direct" access to a PCI device to DomU, is it
> > still being piped through Dom0 like block devices and interfaces?  If
> > so why is this necessary?  Does the device-specific driver run in Dom0
> > or DomU?
> >
> > Thanks,
> > Dave
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
>
>
>

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