linux-kernel - RE: [PATCH 1/4] iommu/vt-d: Implement set device pasid op for default domain

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Date:   Fri, 3 Mar 2023 02:36:24 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Jason Gunthorpe <jgg@...dia.com>,
        Joerg Roedel <joro@...tes.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>
CC:     Robin Murphy <robin.murphy@....com>, Will Deacon <will@...nel.org>,
        "David Woodhouse" <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>
Subject: RE: [PATCH 1/4] iommu/vt-d: Implement set device pasid op for default
 domain

> From: Baolu Lu <baolu.lu@...ux.intel.com>
> Sent: Thursday, March 2, 2023 10:07 PM
> > +
> > +	if (!sm_supported(iommu) || !info)
> 
> @info has been referenced. !info check makes no sense.
> 
> Add pasid_supported(iommu).
> 
> Do you need to check whether the domain is compatible for this rid
> pasid?

what kind of compatibility is concerned here? In concept a pasid
can be attached to any domain if it has been successfully attached
to rid. Probably we can add a check here that RID2PASID must
point to the domain already.

> 
> > +		return -ENODEV;
> > +
> > +	if (WARN_ON(pasid == PASID_RID2PASID))
> > +		return -EINVAL;
> 
> Add a call to domain_attach_iommu() here to get a refcount of the domain
> ID. And call domain_detach_iommu() in intel_iommu_remove_dev_pasid().
> 

Is it necessary? iommu core doesn't allow taking ownership
if !xa_empty(&group->pasid_array) so if this pasid attach succeeds
this device cannot be attached to another domain before pasid
detach is done on the current domain.