linux-kernel - Re: [PATCH v2 3/3] vfio/pci: Don't probe devices that can't be reset

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Date:   Fri, 18 Aug 2017 15:42:31 +0200
From:   Jan Glauber <jan.glauber@...iumnetworks.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, david.daney@...ium.com,
        Jon Masters <jcm@...hat.com>,
        Robert Richter <robert.richter@...ium.com>,
        linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2 3/3] vfio/pci: Don't probe devices that can't be reset

On Thu, Aug 17, 2017 at 07:00:17AM -0600, Alex Williamson wrote:
> On Thu, 17 Aug 2017 10:14:23 +0200
> Jan Glauber <jglauber@...ium.com> wrote:
> 
> > If a PCI device supports neither function-level reset, nor slot
> > or bus reset then refuse to probe it. A line is printed to inform
> > the user.
> 
> But that's not what this does, this requires that the device is on a
> reset-able bus.  This is a massive regression.  With this we could no
> longer assign devices on the root complex or any device which doesn't
> return from bus reset and currently makes use of the NO_BUS_RESET flag
> and works happily otherwise.  Full NAK.  Thanks,

Looks like I missed the slot reset check. So how about this:

if (pci_probe_reset_slot(pdev->slot) && pci_probe_reset_bus(pdev->bus)) {
	dev_warn(...);
	return -ENODEV;
}

Or am I still missing something here?

thanks,
Jan

> Alex
>  
> > Without this change starting qemu with a vfio-pci device can lead to
> > a kernel panic on some Cavium cn8xxx systems, depending on the used
> > device.
> > 
> > Signed-off-by: Jan Glauber <jglauber@...ium.com>
> > ---
> >  drivers/vfio/pci/vfio_pci.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > index 063c1ce..029ba13 100644
> > --- a/drivers/vfio/pci/vfio_pci.c
> > +++ b/drivers/vfio/pci/vfio_pci.c
> > @@ -1196,6 +1196,12 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> >  	if (pdev->hdr_type != PCI_HEADER_TYPE_NORMAL)
> >  		return -EINVAL;
> >  
> > +	ret = pci_probe_reset_bus(pdev->bus);
> > +	if (ret) {
> > +		dev_warn(&pdev->dev, "Refusing to probe because reset is not possible.\n");
> > +		return ret;
> > +	}
> > +
> >  	group = vfio_iommu_group_get(&pdev->dev);
> >  	if (!group)
> >  		return -EINVAL;