Re: [PATCH v3 02/12] vfio/pci: Only check ownership of opened devices in hot reset

Eric Auger
2023-04-04T14:02:02Z

Hi YI,

On 4/1/23 16:44, Yi Liu wrote:
> If the affected device is not opened by any user, it's safe to reset it
> given it's not in use.
>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Tested-by: Yanting Jiang <yanting.jiang@intel.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
> drivers/vfio/pci/vfio_pci_core.c | 14 +++++++++++---
> include/uapi/linux/vfio.h | 8 ++++++++
> 2 files changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 65bbef562268..5d745c9abf05 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -2429,10 +2429,18 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
>
> list_for_each_entry(cur_vma, &dev_set->device_list, vdev.dev_set_list) {
> /*
> - * Test whether all the affected devices are contained by the
> - * set of groups provided by the user.
> + * Test whether all the affected devices can be reset by the
> + * user.
> + *
> + * Resetting an unused device (not opened) is safe, because
> + * dev_set->lock is held in hot reset path so this device
> + * cannot race being opened by another user simultaneously.
> + *
> + * Otherwise all opened devices in the dev_set must be
> + * contained by the set of groups provided by the user.
> */
> - if (!vfio_dev_in_groups(cur_vma, groups)) {
> + if (cur_vma->vdev.open_count &&
> + !vfio_dev_in_groups(cur_vma, groups)) {
> ret = -EINVAL;
> goto err_undo;
> }
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 0552e8dcf0cb..f96e5689cffc 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -673,6 +673,14 @@ struct vfio_pci_hot_reset_info {
> * VFIO_DEVICE_PCI_HOT_RESET - _IOW(VFIO_TYPE, VFIO_BASE + 13,
> * struct vfio_pci_hot_reset)
> *
> + * Userspace requests hot reset for the devices it uses. Due to the
> + * underlying topology, multiple devices can be affected in the reset
by the reset
> + * while some might be opened by another user. To avoid interference
s/interference/hot reset failure?
> + * the calling user must ensure all affected devices, if opened, are
> + * owned by itself.
> + *
> + * The ownership is proved by an array of group fds.
> + *
> * Return: 0 on success, -errno on failure.
> */
> struct vfio_pci_hot_reset {
Thanks

Eric