Re: [RFC PATCH v3 08/15] hw/arm/smmuv3-accel: Add set/unset_iommu_device callback

[Nicolin Chen <nicolinc@nvidia.com>]

On Tue, Jul 15, 2025 at 11:29:41AM +0100, Jonathan Cameron wrote:
> > +    if (!iommufd_backend_alloc_viommu(idev->iommufd, idev->devid,
> > +                                      IOMMU_VIOMMU_TYPE_ARM_SMMUV3,
> > +                                      s2_hwpt_id, &viommu_id, errp)) {
> > +        return false;
> > +    }

[...]

> > +free_abort_hwpt:
> > +    iommufd_backend_free_id(idev->iommufd, viommu->abort_hwpt_id);
> > +free_viommu:
> > +    iommufd_backend_free_id(idev->iommufd, viommu->core.viommu_id);
> > +    g_free(viommu);
> 
> No unwinding of iommufd_backened_alloc_viommu?
> Looks like we just leak it until destruction of the fd. 
> 
> Maybe add a comment for those like me who aren't all that familiar with
> this stuff and see an alloc with no matching free.

Those iommufd_backend_free_id calls are the reverts. An iommufd
object is free-ed using its object id, i.e. the "viommu_id" and
"abort_hwpt_id" in the lines.

Adding comments to every single iommufd_backened_free_id() call
isn't optimal, IMHO, as that function would be invoked across
different vIOMMU files and even the vfio/iommufd core files.

Perhaps QEMU should wrap it up with a helper, E.g.

static inline void iommufd_backend_free(int iommufd, int obj_id)
{
	iommufd_backend_free_id(iommufd, obj_id);
}

if it helps readability?

Nicolin