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

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Message-ID: <20221109043617.GA900761@zander>
Date:   Wed, 9 Nov 2022 04:36:17 +0000
From:   Wei Gong <gongwei833x@...il.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, linux-kernel@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org
Subject: Re: [PATCH v2] pci: fix device presence detection for VFs

O Tue, Nov 08, 2022 at 01:02:35PM -0500, Michael S. Tsirkin wrote:
> On Tue, Nov 08, 2022 at 11:58:53AM -0600, Bjorn Helgaas wrote:
> > 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.
> 
> I was hoping Wei will answer that, I don't have the hardware.

In my case I don't care that VF Enable has been cleared.

> 
> > > > 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 it's a little out-of-date and more restrictive than current practice.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
>