Re: [PATCH v10 06/18] iommufd/device: Add helper to detect the first attach of a group

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Mar 20, 2025 at 06:47:32AM -0700, Yi Liu wrote:
> The existing code detects the first attach by checking the
> igroup->device_list. However, the igroup->hwpt can also be used to detect
> the first attach. In future modifications, it is better to check the
> igroup->hwpt instead of the device_list. To improve readbility and also
> prepare for further modifications on this part, this adds a helper for it.
> 
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
> v9 -> v10: It is patch 07 of v9, it's reworked hence renamed as well.
> ---
>  drivers/iommu/iommufd/device.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> index ac54d734b819..9db36346328f 100644
> --- a/drivers/iommu/iommufd/device.c
> +++ b/drivers/iommu/iommufd/device.c
> @@ -444,6 +444,13 @@ static int iommufd_group_setup_msi(struct iommufd_group *igroup,
>  	return 0;
>  }
>  
> +static inline bool
> +igroup_first_attach(struct iommufd_group *igroup, ioasid_t pasid)
> +{
> +	lockdep_assert_held(&igroup->lock);
> +	return !igroup->hwpt;
> +}
> +
>  static int
>  iommufd_device_attach_reserved_iova(struct iommufd_device *idev,
>  				    struct iommufd_hwpt_paging *hwpt_paging)
> @@ -459,7 +466,7 @@ iommufd_device_attach_reserved_iova(struct iommufd_device *idev,
>  	if (rc)
>  		return rc;
>  
> -	if (list_empty(&igroup->device_list)) {
> +	if (igroup_first_attach(igroup, IOMMU_NO_PASID)) {
>  		rc = iommufd_group_setup_msi(igroup, hwpt_paging);
>  		if (rc) {
>  			iopt_remove_reserved_iova(&hwpt_paging->ioas->iopt,
> @@ -623,7 +630,7 @@ int iommufd_hw_pagetable_attach(struct iommufd_hw_pagetable *hwpt,
>  	 * reserved regions are only updated during individual device
>  	 * attachment.
>  	 */
> -	if (list_empty(&igroup->device_list)) {
> +	if (igroup_first_attach(igroup, pasid)) {
>  		rc = iommufd_hwpt_attach_device(hwpt, idev, pasid);
>  		if (rc)
>  			goto err_unresv;

We have the same list_empty in the iommufd_hw_pagetable_detach()
and iommufd_group_release() too?

And I feel "igroup_is_not_attached" could be clearer, as it fits
the detach/release context too.

Thanks
Nicolin