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 10:37:01AM -0700, Nicolin Chen wrote:
> 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.

Oh, I just found that the following patch changes those paths.

Yet, at the end of the series this igroup_first_attach() is quite
similar to iommufd_device_is_attached(). So, maybe we could align
with that the naming here: iommufd_group_is_attached?

With that,
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>