Re: [PATCH v3 03/16] iommufd/viommu: Add IOMMU_VDEVICE_ALLOC ioctl

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Oct 09, 2024 at 09:38:15AM -0700, Nicolin Chen wrote:
> +void iommufd_vdevice_destroy(struct iommufd_object *obj)
> +{
> +	struct iommufd_vdevice *old, *vdev =
> +		container_of(obj, struct iommufd_vdevice, obj);
> +	struct iommufd_viommu *viommu = vdev->viommu;
> +	struct iommufd_device *idev = vdev->idev;
> +
> +	if (viommu->ops && viommu->ops->vdevice_free)
> +		viommu->ops->vdevice_free(vdev);
> +
> +	old = xa_cmpxchg(&viommu->vdevs, vdev->id, vdev, NULL, GFP_KERNEL);
> +	if (old)
> +		WARN_ON(old != vdev);
> +
> +	refcount_dec(&viommu->obj.users);
> +	refcount_dec(&idev->obj.users);
> +	idev->vdev = NULL;

This should hold the igroup lock when touching vdev?

> +int iommufd_vdevice_alloc_ioctl(struct iommufd_ucmd *ucmd)
> +{
> +	struct iommu_vdevice_alloc *cmd = ucmd->cmd;
> +	struct iommufd_vdevice *vdev, *curr;
> +	struct iommufd_viommu *viommu;
> +	struct iommufd_device *idev;
> +	u64 virt_id = cmd->virt_id;
> +	int rc = 0;
> +
> +	if (virt_id > ULONG_MAX)
> +		return -EINVAL;
> +
> +	viommu = iommufd_get_viommu(ucmd, cmd->viommu_id);
> +	if (IS_ERR(viommu))
> +		return PTR_ERR(viommu);
> +
> +	idev = iommufd_get_device(ucmd, cmd->dev_id);
> +	if (IS_ERR(idev)) {
> +		rc = PTR_ERR(idev);
> +		goto out_put_viommu;
> +	}
> +
> +	mutex_lock(&idev->igroup->lock);
> +	if (idev->vdev) {
> +		rc = -EEXIST;
> +		goto out_unlock_igroup;
> +	}

Otherwise this won't work right

> +	if (viommu->ops && viommu->ops->vdevice_alloc)
> +		vdev = viommu->ops->vdevice_alloc(viommu, idev->dev, virt_id);
> +	else
> +		vdev = __iommufd_vdevice_alloc(ucmd->ictx, sizeof(*vdev));
> +	if (IS_ERR(vdev)) {
> +		rc = PTR_ERR(vdev);
> +		goto out_unlock_igroup;
> +	}
> +
> +	vdev->idev = idev;
> +	vdev->id = virt_id;
> +	vdev->viommu = viommu;
> +
> +	idev->vdev = vdev;
> +	refcount_inc(&idev->obj.users);
> +	refcount_inc(&viommu->obj.users);
> +
> +	curr = xa_cmpxchg(&viommu->vdevs, virt_id, NULL, vdev, GFP_KERNEL);
> +	if (curr) {
> +		rc = xa_err(curr) ? : -EBUSY;
> +		goto out_abort;
> +	}
> +
> +	cmd->out_vdevice_id = vdev->obj.id;
> +	rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
> +	if (rc)
> +		goto out_abort;
> +	iommufd_object_finalize(ucmd->ictx, &vdev->obj);
> +	goto out_unlock_igroup;
> +
> +out_abort:
> +	iommufd_object_abort_and_destroy(ucmd->ictx, &vdev->obj);

But be mindful of this abort, it doesn't want to be inside the lock if
it also gets the lock.. fail_nth should be updated to cover these new
ioctls to look for tricky things like that

But the design looks OK

Jason