linux-kernel - Re: [PATCH v2 4/7] iommu: Let iommu.strict override ops->def_domain

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Date:   Wed, 7 Dec 2022 10:30:42 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>, iommu@...ts.linux.dev,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>,
        linux-s390@...r.kernel.org, borntraeger@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, linux-kernel@...r.kernel.org,
        Julian Ruess <julianr@...ux.ibm.com>
Subject: Re: [PATCH v2 4/7] iommu: Let iommu.strict override
 ops->def_domain_type

On Wed, Dec 07, 2022 at 02:18:36PM +0000, Robin Murphy wrote:
> On 2022-12-07 13:23, Jason Gunthorpe wrote:
> > On Wed, Dec 07, 2022 at 09:18:19PM +0800, Baolu Lu wrote:
> > 
> > > > -	/* Check if the device in the group still has a driver bound to it */
> > > > -	device_lock(dev);
> > > 
> > > With device_lock() removed, this probably races with the
> > > iommu_release_device() path? group->mutex seems insufficient to avoid
> > > the race. Perhaps I missed anything.
> > 
> > This path only deals with group, so there is no 'dev' and no race with
> > removal.
> 
> If we can now use the ownership mechanism to enforce the required
> constraints for change_dev_def_domain, that would be worthwhile (and a lot
> clearer) as a separate patch in its own right.

Oh for sure, this is just a brain dump to share

I have a few other patches streamlining things in this file, just need time...

Jason