Re: [Xen-devel] xen-pciback.hide syntax

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Jul 30, 2012 at 09:47:41PM +0200, Sander Eikelenboom wrote:
> Monday, July 30, 2012, 9:00:06 PM, you wrote:
> 
> > On Sat, May 19, 2012 at 10:46:15AM +0200, Sander Eikelenboom wrote:
> >> Hi Konrad,
> >> 
> >> The syntax for specifying the devices for pciback to hide is 
> >> "bus:device.function".
> >> While thinking about cooking up a patch to be able to use a "*" wildcard 
> >> for the function, i was wondering if not hiding all functions of a device 
> >> is feasible at all.
> >> 
> >> For what I understand of PCI, function 0 is always required, so if I only 
> >> hide function 0, i can't use the other functions in dom0, since those 
> >> functions would require a function 0, which is hidden.
> >> 
> >> So would it be more logical to drop/ignore the function from the BDF, and 
> >> always hide all functions from a device ?
> 
> > That might run afoul of the SR-IOV virtual devices. They (when loaded) 
> > provide a fake
> > bus:device:function, where the device is port (so if the SR-IOV card has two
> > jacks, you get 00 and 01), and the function is for the amount of VFs it can 
> > make.
> > On the Intel SR-IOV NIC with 'igbvf.max_vfs=7' I end up with 14 PCI 
> > devices, where
> > the function bear no resemblence to each other (and can be passed in 
> > different guests).
> 
> > The PCI restriction I know of is if the device is behind a bridge. The 
> > issue here
> > is that .. well, you could pass in a different function to a different 
> > guest, but
> > one guest's hardware device could listen on the other guests' function. It 
> > would
> > require tweaking the driver to dump the contents of some registers and some 
> > deep
> > hacking, but that is the security issue with that.
> 
> Hmm that would mean there are three possibilities:
> 1) Accept a Wildcard syntax like "bus:device.*", which would mean hide all 
> functions of device.

Which in this context actually makes sense. You probably don't want to use the 
VF's in
your host.

> 2) Accept not providing the function as a wildcard "bus:device", would mean 
> hide all functions of device.

<nods>.
> 
> 3) Do nothing, the gained overview on grub lines isn't worth the effort :-)

Heh!

I think I like 2).

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