[PATCH v3 00/12] Introduce new methods for verifying ownership in vfio PCI hot reset

Yi Liu
2023-04-01T14:44:33Z

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] [7], in the
end of this series, the VFIO_DEVICE_GET_PCI_HOT_RESET_INFO is extended
to report devid for the devices opened as cdev. This is goging to support
the device fd passing usage.

The new hot reset method and updated _INFO ioctl are tested with two
test commits in below qemu:

https://github.com/yiliu1765/qemu/commits/iommufd_rfcv3
(requires to test with cdev kernel)

[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/
[7] https://lore.kernel.org/kvm/20230327132619.5ab15440.alex.williamson@redhat.com/

Change log:

v3:
- Remove the new _INFO ioctl of v2, extend the existing _INFO ioctl to
report devid (Alex)
- Add r-b from Jason
- Add t-b from Terrence Xu and Yanting Jiang (mainly regression test)

v2: https://lore.kernel.org/kvm/20230327093458.44939-1-yi.l.liu@intel.com/
- 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 (12):
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: Mark cdev usage in vfio_device
iommufd: Define IOMMUFD_INVALID_ID in uapi
vfio/pci: Report dev_id in VFIO_DEVICE_GET_PCI_HOT_RESET_INFO

drivers/iommu/iommufd/device.c | 12 ++
drivers/vfio/group.c | 32 +++--
drivers/vfio/iommufd.c | 14 +++
drivers/vfio/pci/vfio_pci_core.c | 204 ++++++++++++++++++++++---------
drivers/vfio/vfio.h | 2 +
drivers/vfio/vfio_main.c | 44 +++++++
include/linux/iommufd.h | 3 +
include/linux/vfio.h | 21 ++++
include/uapi/linux/iommufd.h | 3 +
include/uapi/linux/vfio.h | 42 ++++++-
10 files changed, 301 insertions(+), 76 deletions(-)

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2.34.1