linux-kernel - Re: [PATCH v6 08/12] iommu/sva: Use attach/detach_pasid

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Date:   Thu, 12 May 2022 08:51:36 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 08/12] iommu/sva: Use attach/detach_pasid_dev in SVA
 interfaces

On Thu, May 12, 2022 at 11:02:39AM +0800, Baolu Lu wrote:
> > > +       mutex_lock(&group->mutex);
> > > +       domain = xa_load(&group->pasid_array, pasid);
> > > +       if (domain && domain->type != type)
> > > +               domain = NULL;
> > > +       mutex_unlock(&group->mutex);
> > > +       iommu_group_put(group);
> > > +
> > > +       return domain;
> > This is bad locking, group->pasid_array values cannot be taken outside
> > the lock.
> 
> It's not iommu core, but SVA (or other feature components) that manage
> the life cycle of a domain. The iommu core only provides a place to
> store the domain pointer. The feature components are free to fetch their
> domain pointers from iommu core as long as they are sure that the domain
> is alive during use.

I'm not convinced.

Jason