Re: [PATCH v2] pci: fix device presence detection for VFs

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Nov 08, 2022 at 10:19:07AM -0500, Michael S. Tsirkin wrote:
> On Tue, Nov 08, 2022 at 09:02:28AM -0600, Bjorn Helgaas wrote:
> > On Tue, Nov 08, 2022 at 08:53:00AM -0600, Bjorn Helgaas wrote:
> > > On Wed, Oct 26, 2022 at 02:11:21AM -0400, Michael S. Tsirkin wrote:
> > > > virtio uses the same driver for VFs and PFs.  Accordingly,
> > > > pci_device_is_present is used to detect device presence. This function
> > > > isn't currently working properly for VFs since it attempts reading
> > > > device and vendor ID.
> > > 
> > > > As VFs are present if and only if PF is present,
> > > > just return the value for that device.
> > > 
> > > VFs are only present when the PF is present *and* the PF has VF Enable
> > > set.  Do you care about the possibility that VF Enable has been
> > > cleared?

I think you missed this question.

> > Can you also include a hint about how the problem manifests, and a URL
> > to the report if available?
> 
> Here you go:
> lore.kernel.org/all/20221108044819.GA861843%40zander/t.mbox.gz
> 
> is it enough to include this link or do you want me
> to repost copying the text from there?

Uh, well, OK, I guess I could dig through that and figure what what's
relevant.  I'd like the commit log to contain a hint of what the
problem looks like and some justification for why it should be
backported to stable.

I still look at Documentation/process/stable-kernel-rules.rst
occasionally to decide things like this, but I get the feeling that
it's a little out-of-date and more restrictive than current practice.

But I do think the "PF exists but VF disabled" situation needs to be
clarified somehow, too.

Bjorn