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

[Samiullah Khawaja <skhawaja@google.com>]

On Wed, Aug 05, 2026 at 09:34:32AM +0000, Tian, Kevin wrote:
>> From: Samiullah Khawaja <skhawaja@google.com>
>> 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@google.com>
>> ---
>>  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