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

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 31 Mar 2023 17:27:27 +0000
"Xu, Terrence" <terrence.xu@intel.com> wrote:

> > -----Original Message-----
> > From: Liu, Yi L <yi.l.liu@intel.com>
> > Sent: Monday, March 27, 2023 5:35 PM
> > 
> > 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.
> > 
> > [1] https://lore.kernel.org/kvm/Y%2FdobS6gdSkxnPH7@nvidia.com/
> > [2] https://lore.kernel.org/kvm/Y%2FZOOClu8nXy2toX@nvidia.com/#t
> > [3] https://lore.kernel.org/kvm/ZACX+Np%2FIY7ygqL5@nvidia.com/
> > [4]
> > https://lore.kernel.org/kvm/DS0PR11MB7529BE88460582BD599DC1F7C3B19
> > @DS0PR11MB7529.namprd11.prod.outlook.com/#t
> > [5] https://lore.kernel.org/kvm/ZAcvzvhkt9QhCmdi@nvidia.com/
> > [6] https://lore.kernel.org/kvm/ZBoYgNq60eDpV9Un@nvidia.com/
> > 
> > Change log:
> > 
> > v2:
> >  - Split the patch 03 of v1 to be 03, 04 and 05 of v2 (Jaon)
> >  - Add r-b from Kevin and Jason
> >  - Add patch 10 to introduce a new _INFO ioctl for the usage of device
> >    fd passing usage in cdev path (Jason, Alex)
> > 
> > v1: https://lore.kernel.org/kvm/20230316124156.12064-1-yi.l.liu@intel.com/
> > 
> > Regards,
> > 	Yi Liu
> > 
> > Yi Liu (10):
> >   vfio/pci: Update comment around group_fd get in
> >     vfio_pci_ioctl_pci_hot_reset()
> >   vfio/pci: Only check ownership of opened devices in hot reset
> >   vfio/pci: Move the existing hot reset logic to be a helper
> >   vfio-iommufd: Add helper to retrieve iommufd_ctx and devid for
> >     vfio_device
> >   vfio/pci: Allow passing zero-length fd array in
> >     VFIO_DEVICE_PCI_HOT_RESET
> >   vfio: Refine vfio file kAPIs for vfio PCI hot reset
> >   vfio: Accpet device file from vfio PCI hot reset path
> >   vfio/pci: Renaming for accepting device fd in hot reset path
> >   vfio/pci: Accept device fd in VFIO_DEVICE_PCI_HOT_RESET ioctl
> >   vfio/pci: Add VFIO_DEVICE_GET_PCI_HOT_RESET_GROUP_INFO
> > 
> >  drivers/iommu/iommufd/device.c   |  12 ++
> >  drivers/vfio/group.c             |  32 ++--
> >  drivers/vfio/iommufd.c           |  16 ++
> >  drivers/vfio/pci/vfio_pci_core.c | 244 ++++++++++++++++++++++++-------
> >  drivers/vfio/vfio.h              |   2 +
> >  drivers/vfio/vfio_main.c         |  44 ++++++
> >  include/linux/iommufd.h          |   3 +
> >  include/linux/vfio.h             |  14 ++
> >  include/uapi/linux/vfio.h        |  65 +++++++-
> >  9 files changed, 364 insertions(+), 68 deletions(-)
> > 
> > --
> > 2.34.1  
> 
> Verified this series by "Intel GVT-g GPU device mediated passthrough".
> Passed VFIO legacy mode / compat mode / cdev mode basic functionality and GPU force reset test.
> 
> Tested-by: Terrence Xu <terrence.xu@intel.com>

Seems like only this "GPU force reset test" is relevant to the new
functionality of this series, GVT-g does not and has no reason to
support the HOT_RESET ioctls used here.  Can you provide more details
of the force-reset test?  What userspace driver is being used?  Thanks,

Alex