linux-kernel - RE: [PATCH v3 3/5] iommu: Add iommu_get_domain_for_dev

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Message-ID: <BN9PR11MB5276CCC219B8456DAF289AD78C32A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Thu, 21 Aug 2025 08:07:01 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Nicolin Chen <nicolinc@...dia.com>
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Subject: RE: [PATCH v3 3/5] iommu: Add iommu_get_domain_for_dev_locked()
 helper

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Saturday, August 16, 2025 2:45 AM
> 
> On Fri, Aug 15, 2025 at 08:55:28AM +0000, Tian, Kevin wrote:
> > > From: Nicolin Chen <nicolinc@...dia.com>
> > > Sent: Tuesday, August 12, 2025 6:59 AM
> > > So, iommu_get_domain_for_dev() should check the gdev flag and return
> the
> > > blocked domain if the flag is set. But the caller of this API could hold
> > > the group->mutex already or not, making it difficult to add the lock.
> > >
> > > Introduce a new iommu_get_domain_for_dev_locked() helper to be used
> by
> > > those drivers in a context that is already under the protection of the
> > > group->mutex, e.g. those attach_dev callback functions. And roll out the
> > > new helper to all the existing IOMMU drivers.
> >
> > iommu_get_domain_for_dev() is also called outside of attach_dev
> > callback functions, e.g. malidp_get_pgsize_bitmap(). and the returned
> > info according to the attached domain might be saved in static
> > structures, e.g.:
> >
> > 	ms->mmu_prefetch_pgsize = malidp_get_pgsize_bitmap(mp);
> >
> > would that cause weird issues when blocking domain is returned
> > though one may not expect reset to happen at that point?
> 
> We aren't changing the iommu_get_domain_for_dev(). So, it should
> be used exclusively for functions that are outside group->mutex,
> like this one, i.e. they should still get the group->domain v.s.
> the blocked domain.
> 

Usually the difference between func() and func_locked() is only about
whether the caller holds a lock. If they mean to return different
domains, may need better naming (though I don't have a good option
now)...