Re: [PATCH v2 3/8] iommu/vt-d: Implement device_pasid domain attach ops

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

Hi Jason,

On Tue, 15 Mar 2022 11:33:22 -0300, Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Mon, Mar 14, 2022 at 10:07:07PM -0700, Jacob Pan wrote:
> > +	/*
> > +	 * Each domain could have multiple devices attached with
> > shared or per
> > +	 * device PASIDs. At the domain level, we keep track of unique
> > PASIDs and
> > +	 * device user count.
> > +	 * E.g. If a domain has two devices attached, device A has
> > PASID 0, 1;
> > +	 * device B has PASID 0, 2. Then the domain would have PASID
> > 0, 1, 2.
> > +	 */  
> 
> A 2d array of xarray's seems like a poor data structure for this task.
> 
> AFACIT this wants to store a list of (device, pasid) tuples, so a
> simple linked list, 1d xarray vector or a red black tree seems more
> appropriate..
> 
Agreed.
It might need some surgery for dmar_domain and device_domain_info, which
already has a simple device list. I am trying to leverage the existing data
struct, let me take a closer look.

> > +	if (entry) {
> > +		pinfo = entry;
> > +	} else {
> > +		pinfo = kzalloc(sizeof(*pinfo), GFP_ATOMIC);
> > +		if (!pinfo)
> > +			return -ENOMEM;
> > +		pinfo->pasid = pasid;
> > +		/* Store the new PASID info in the per domain array */
> > +		ret = xa_err(__xa_store(&dmar_domain->pasids, pasid,
> > pinfo,
> > +			     GFP_ATOMIC));
> > +		if (ret)
> > +			goto xa_store_err;
> > +	}
> > +	/* Store PASID in per device-domain array, this is for
> > tracking devTLB */
> > +	ret = xa_err(xa_store(&info->pasids, pasid, pinfo,
> > GFP_ATOMIC));
> > +	if (ret)
> > +		goto xa_store_err;
> > +
> > +	atomic_inc(&pinfo->users);
> > +	xa_unlock(&dmar_domain->pasids);
> > +
> > +	return 0;
> > +
> > +xa_store_err:
> > +	xa_unlock(&dmar_domain->pasids);
> > +	spin_lock_irqsave(&iommu->lock, flags);
> > +	intel_pasid_tear_down_entry(iommu, dev, pasid, false);
> > +	spin_unlock_irqrestore(&iommu->lock, flags);
> > +
> > +	if (!atomic_read(&pinfo->users)) {
> > +		__xa_erase(&dmar_domain->pasids, pasid);  
> 
> This isn't locked right
> 
good catch! need to move under xa_unlock.

Thanks,

Jacob