Re: [RFC PATCH 1/1] vfio/pci: Disable sriov on PF device close

[Samiullah Khawaja]

On Wed, Aug 05, 2026 at 09:34:32AM +0000, Tian, Kevin wrote:
> > From: Samiullah Khawaja <skhawaja@xxxxxxxxxx>
> > Sent: Wednesday, August 5, 2026 8:34 AM
> >
> > When userspace closes a VFIO device file descriptor, the vfio driver
> > performs a hardware reset on the PCIe device to ensure it is returned to
> > a clean state. However, if the closed device is an SR-IOV Physical
> > Function (PF), it may have instantiated Virtual Functions (VFs) that are
> > actively bound to host kernel drivers (or other vfio instances).
> >
> > When the PF is hardware-reset via VFIO, it implicitly disrupts SR-IOV
> > operations at the device level. Because this reset happens without notifying
> > the core PCI driver model, the kernel drivers bound to the VFs remain loaded
> > and operate under the assumption that the VF hardware is still functional.
> >
> > This creates a state mismatch between the kernel's view of the hardware
> > and the actual device state. Subsequent attempts by the host OS or bound
> > drivers to interact with the VFs will fail, leading to unexpected
> > errors.
> >
> > Disable SR-IOV on the device prior to issuing the PF reset so that the
> > VFs can teardown and remove at the software level also.
> >
> > Signed-off-by: Samiullah Khawaja <skhawaja@xxxxxxxxxx>
> > ---
> >  drivers/vfio/pci/vfio_pci_core.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> > index a113c55845e1..b36c77eb3c40 100644
> > --- a/drivers/vfio/pci/vfio_pci_core.c
> > +++ b/drivers/vfio/pci/vfio_pci_core.c
> > @@ -826,6 +826,13 @@ void vfio_pci_core_close_device(struct vfio_device
> > *core_vdev)
> >  #if IS_ENABLED(CONFIG_EEH)
> >  	eeh_dev_release(vdev->pdev);
> >  #endif
> > +
> > +	if (pci_num_vf(vdev->pdev)) {
> > +		device_lock(&vdev->pdev->dev);
> > +		vfio_pci_core_sriov_configure(vdev, 0);
> > +		device_unlock(&vdev->pdev->dev);
> > +	}
> > +
>
> Sashiko reported several locking issues with this change:
>
> https://sashiko.dev/#/patchset/20260805003355.728299-2-skhawaja%40google.com
>
> Actually it is a discouraged usage allowing kernel drivers bound to VFs
> which belongs to a PF owned by vfio userspace.

Thanks for the feedback Kevin.

I sent this as an RFC specifically to discuss the right approach for
resolving this issue before fixing the locking issues that sashiko
raised. I will get back to this once the discussion to fix this the
right way concludes in the other thread.

Thanks,
Sami