Re: [PATCH v2 00/10] Introduce new methods for verifying ownership in vfio PCI hot reset

Alex Williamson
2023-03-31T13:25:31Z

On Fri, 31 Mar 2023 03:14:23 +0000
"Jiang, Yanting" <yanting.jiang@intel.com> wrote:

> >
> > VFIO_DEVICE_PCI_HOT_RESET requires user to pass an array of group fds to
> > prove that it owns all devices affected by resetting the calling device. This series
> > introduces several extensions to allow the ownership check better aligned with
> > iommufd and coming vfio device cdev support.
> >
> > First, resetting an unopened device is always safe given nobody is using it. So
> > relax the check to allow such devices not covered by group fd array. [1]
> >
> > When iommufd is used we can simply verify that all affected devices are bound
> > to a same iommufd then no need for the user to provide extra fd information.
> > This is enabled by the user passing a zero-length fd array and moving forward
> > this should be the preferred way for hot reset. [2]
> >
> > However the iommufd method has difficulty working with noiommu devices
> > since those devices don't have a valid iommufd, unless the noiommu device is in
> > a singleton dev_set hence no ownership check is required. [3]
> >
> > For noiommu backward compatibility a 3rd method is introduced by allowing the
> > user to pass an array of device fds to prove ownership. [4]
> >
> > As suggested by Jason [5], we have this series to introduce the above stuffs to
> > the vfio PCI hot reset. Per the dicussion in [6], this series also adds a new _INFO
> > ioctl to get hot reset scope for given device.
> >
> Tested NIC passthrough on Intel platform.
> Result looks good hence,
> Tested by: Jiang, Yanting <yanting.jiang@intel.com>

I'm not aware of any userspace that exercises this reset ioctl in cdev
mode. Is this regression testing only? Thanks,

Alex