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

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Hello Konrad,

Tuesday, July 31, 2012, 5:25:58 PM, you wrote:

> 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.

In my use cases i always hide all functions, and since my usb controllers have 
7 functions, that leads to quite some long lines.

>> 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).

I think that would be the most simple and straightforward to implement, the 
only thing is that the .cfg files seem to use the "bus:device.*" scheme ...
Don't know if there are any other related cmd options for the kernel that use a 
certain syntax that could be preferred ?

--

Sander


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