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

[Baolu Lu]

On 4/18/23 12:46 AM, Jacob Pan wrote:
> On Wed, 12 Apr 2023 09:37:48 +0800, Baolu Lu<baolu.lu@xxxxxxxxxxxxxxx>
> wrote:
>
> > On 4/11/23 4:02 PM, Tian, Kevin wrote:
> > > > From: Jacob Pan<jacob.jun.pan@xxxxxxxxxxxxxxx>
> > > > 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?

Probably we can introduce a counterpart dev->iommu->min_pasids, so that
there's no need to reserve the RID_PASID. At present, we can set it to 1
in the core as ARM/AMD/Intel all treat PASID 0 as a special pasid.

In the future, if VT-d supports using arbitrary number as RID_PASID for
any specific device, we can call iommu_alloc_global_pasid() for that
device.

The device drivers don't know and don't need to know the range of viable
PASIDs, so the @min, @max parameters seem to be unreasonable.

Best regards,
baolu