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

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Date:   Thu, 17 Aug 2017 07:00:17 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jan Glauber <jglauber@...ium.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, 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,

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;