Re: Xen 4.2 Release Plan / TODO

[Keir Fraser <keir@xen.org>]

On 22/03/2012 10:19, "Ian Campbell" <Ian.Campbell@citrix.com> wrote:

> I told a lie -- the code does seem to be there in
> mainline
(drivers/xen/xen-pciback/conf_space_quirks.c et al). Not sure how
> grep
missed it.

Does anyone know what the actual purpose/function of the
> single defined
quirk is? 10845:df80de098d15 which introduces it doesn't really
> say,
it's just a bunch of magic register frobbing as far as I'm concerned.

I
> guess you have a tg3 and are suffering from this exact quirk?

It's an awful
> lot of scaffolding on both the userspace and kernel side
to support a generic
> quirks system which has had exactly one quirk since
it was introduced in mid
> 2006. Perhaps we should just address the
specific tg3 issue directly?


The issue is that 'quirk' is something of a misnomer. Many devices may have
device-specific registers exposed via their PCI config space. The default
pciback policy is set to allow only known generic PCI config space registers
to be accessed by a guest. This will fail for likely a fair few devices, and
the most common solution is to set the pciback.permissive flag and just
allow guest access to all of the device's PCI config space. This is far less
hassle than actually setting up a proper 'quirk' and frankly most people
trust the device drivers they run, even if they are in a domU. I wonder how
many people really give a crap about the protection of !pciback.permissive.

 -- Keir