Re: [PATCH v4 3/7] iommu: Support allocation of global PASIDs outside SVA

Jacob Pan
2023-04-17T16:05:09Z

Hi Kevin,

On Tue, 11 Apr 2023 08:02:55 +0000, "Tian, Kevin" <kevin.tian@intel.com>
wrote:

> > From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > Sent: Saturday, April 8, 2023 2:06 AM
> > @@ -28,8 +26,8 @@ static int iommu_sva_alloc_pasid(struct mm_struct
> > *mm, ioasid_t min, ioasid_t ma
> > goto out;
> > }
> >
> > - ret = ida_alloc_range(&iommu_global_pasid_ida, min, max,
> > GFP_KERNEL);
> > - if (ret < min)
> > + ret = iommu_alloc_global_pasid(min, max);
>
> I wonder whether this can take a device pointer so dev->iommu->max_pasids
> is enforced inside the alloc function.
>
> and do we even need the min/max parameters? With special pasids reserved
> then what driver needs is just to get a free pasid from the global space
> within dev->iommu->max_pasids constraint...
>
> iommu_sva_alloc_pasid() can be reworked to avoid min/max by taking a
> device pointer too.
I think that will work too albeit a philosophical change. It probably
should be called iommu_alloc_dev_global_pasid(dev).

But I feel the current approach is more flexible in that device drivers
can control the range if for some reason it does not want go max_pasid.

Thanks,

Jacob