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

Jacob Pan
2023-04-17T16:45:25Z

Hi Baolu,

On Wed, 12 Apr 2023 09:37:48 +0800, Baolu Lu <baolu.lu@linux.intel.com>
wrote:

> On 4/11/23 4:02 PM, Tian, Kevin 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.
>
> Agreed. Instead of using the open code, it looks better to have a helper
> like dev_iommu_max_pasids().
yes, probably export dev_iommu_get_max_pasids(dev)?

But if I understood Kevin correctly, he's also suggesting that the
interface should be changed to iommu_alloc_global_pasid(dev), my concern is
that how do we use this function to reserve RID_PASID which is not specific
to a device?

>
> >
> > 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.
>
> Best regards,
> baolu

Thanks,

Jacob