Re: [PATCH v3 05/12] vfio/pci: Allow passing zero-length fd array in VFIO_DEVICE_PCI_HOT_RESET

Eric Auger
2023-04-04T16:56:26Z

Hi Yi,

On 4/1/23 16:44, Yi Liu wrote:
> as an alternative method for ownership check when iommufd is used. In
I don't understand the 1st sentence.
> this case all opened devices in the affected dev_set are verified to
> be bound to a same valid iommufd value to allow reset. It's simpler
> and faster as user does not need to pass a set of fds and kernel no
kernel does not need to search
> need to search the device within the given fds.
>
> a device in noiommu mode doesn't have a valid iommufd, so this method
> should not be used in a dev_set which contains multiple devices and one
> of them is in noiommu. The only allowed noiommu scenario is that the
> calling device is noiommu and it's in a singleton dev_set.
>
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.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 | 42 +++++++++++++++++++++++++++-----
> include/uapi/linux/vfio.h | 9 ++++++-
> 2 files changed, 44 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
> index 3696b8e58445..b68fcba67a4b 100644
> --- a/drivers/vfio/pci/vfio_pci_core.c
> +++ b/drivers/vfio/pci/vfio_pci_core.c
> @@ -180,7 +180,8 @@ static void vfio_pci_probe_mmaps(struct vfio_pci_core_device *vdev)
> struct vfio_pci_group_info;
> static void vfio_pci_dev_set_try_reset(struct vfio_device_set *dev_set);
> static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
> - struct vfio_pci_group_info *groups);
> + struct vfio_pci_group_info *groups,
> + struct iommufd_ctx *iommufd_ctx);
>
> /*
> * INTx masking requires the ability to disable INTx signaling via PCI_COMMAND
> @@ -1277,7 +1278,7 @@ vfio_pci_ioctl_pci_hot_reset_groups(struct vfio_pci_core_device *vdev,
> return ret;
>
> /* Somewhere between 1 and count is OK */
> - if (!hdr->count || hdr->count > count)
> + if (hdr->count > count)
then I would simply remove the above comment since !count check is done
by the caller.
> return -EINVAL;
>
> group_fds = kcalloc(hdr->count, sizeof(*group_fds), GFP_KERNEL);
> @@ -1326,7 +1327,7 @@ vfio_pci_ioctl_pci_hot_reset_groups(struct vfio_pci_core_device *vdev,
> info.count = hdr->count;
> info.files = files;
>
> - ret = vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, &info);
> + ret = vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, &info, NULL);
>
> hot_reset_release:
> for (file_idx--; file_idx >= 0; file_idx--)
> @@ -1341,6 +1342,7 @@ static int vfio_pci_ioctl_pci_hot_reset(struct vfio_pci_core_device *vdev,
> {
> unsigned long minsz = offsetofend(struct vfio_pci_hot_reset, count);
> struct vfio_pci_hot_reset hdr;
> + struct iommufd_ctx *iommufd;
> bool slot = false;
>
> if (copy_from_user(&hdr, arg, minsz))
> @@ -1355,7 +1357,12 @@ static int vfio_pci_ioctl_pci_hot_reset(struct vfio_pci_core_device *vdev,
> else if (pci_probe_reset_bus(vdev->pdev->bus))
> return -ENODEV;
>
> - return vfio_pci_ioctl_pci_hot_reset_groups(vdev, &hdr, slot, arg);
> + if (hdr.count)
> + return vfio_pci_ioctl_pci_hot_reset_groups(vdev, &hdr, slot, arg);
> +
> + iommufd = vfio_iommufd_physical_ictx(&vdev->vdev);
> +
> + return vfio_pci_dev_set_hot_reset(vdev->vdev.dev_set, NULL, iommufd);
> }
>
> static int vfio_pci_ioctl_ioeventfd(struct vfio_pci_core_device *vdev,
> @@ -2327,6 +2334,9 @@ static bool vfio_dev_in_groups(struct vfio_pci_core_device *vdev,
> {
> unsigned int i;
>
> + if (!groups)
> + return false;
> +
> for (i = 0; i < groups->count; i++)
> if (vfio_file_has_dev(groups->files[i], &vdev->vdev))
> return true;
> @@ -2402,13 +2412,25 @@ static int vfio_pci_dev_set_pm_runtime_get(struct vfio_device_set *dev_set)
> return ret;
> }
>
> +static bool vfio_dev_in_iommufd_ctx(struct vfio_pci_core_device *vdev,
> + struct iommufd_ctx *iommufd_ctx)
> +{
> + struct iommufd_ctx *iommufd = vfio_iommufd_physical_ictx(&vdev->vdev);
> +
> + if (!iommufd)
> + return false;
> +
> + return iommufd == iommufd_ctx;
> +}
> +
> /*
> * We need to get memory_lock for each device, but devices can share mmap_lock,
> * therefore we need to zap and hold the vma_lock for each device, and only then
> * get each memory_lock.
> */
> static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
> - struct vfio_pci_group_info *groups)
> + struct vfio_pci_group_info *groups,
> + struct iommufd_ctx *iommufd_ctx)
> {
> struct vfio_pci_core_device *cur_mem;
> struct vfio_pci_core_device *cur_vma;
> @@ -2448,9 +2470,17 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
> *
> * Otherwise all opened devices in the dev_set must be
> * contained by the set of groups provided by the user.
> + *
> + * If user provides a zero-length array, then all the
> + * opened devices must be bound to a same iommufd_ctx.
> + *
> + * If all above checks are failed, reset is allowed only if
> + * the calling device is in a singleton dev_set.
> */
> if (cur_vma->vdev.open_count &&
> - !vfio_dev_in_groups(cur_vma, groups)) {
> + !vfio_dev_in_groups(cur_vma, groups) &&
> + !vfio_dev_in_iommufd_ctx(cur_vma, iommufd_ctx) &&
> + (dev_set->device_count > 1)) {
> ret = -EINVAL;
> goto err_undo;
> }
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index f96e5689cffc..17aa5d09db41 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -679,7 +679,14 @@ struct vfio_pci_hot_reset_info {
> * the calling user must ensure all affected devices, if opened, are
> * owned by itself.
> *
> - * The ownership is proved by an array of group fds.
> + * The ownership can be proved by:
> + * - An array of group fds
> + * - A zero-length array

I would suggest something alike
in case a non void group fd array is passed, the devices affected by the
reset must belong to those opened VFIO groups.
in case a zero length array is passed, the other devices affected by the
reset, if any, must be bound to the same iommufd as this VFIO device
Either of the 2 methods is applied to check the feasibility of the reset
> + *
> + * In the last case all affected devices which are opened by this user
> + * must have been bound to a same iommufd. If the calling device is in
> + * noiommu mode (no valid iommufd) then it can be reset only if the reset
> + * doesn't affect other devices.
and keep that too
> *
> * Return: 0 on success, -errno on failure.
> */
Thanks

Eric