linux-kernel - Re: [PATCH v4 5/7] iommu: Add iommu_get_domain_for_dev

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Message-ID: <aNRLOsomtHNumaSY@Asurada-Nvidia>
Date: Wed, 24 Sep 2025 12:49:14 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
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Subject: Re: [PATCH v4 5/7] iommu: Add iommu_get_domain_for_dev_locked()
 helper

On Wed, Sep 24, 2025 at 04:10:55PM -0300, Jason Gunthorpe wrote:
> On Sun, Aug 31, 2025 at 04:31:57PM -0700, Nicolin Chen wrote:
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index ea2ef53bd4fef..99680cdb57265 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -2097,7 +2097,7 @@ EXPORT_SYMBOL_GPL(dma_iova_destroy);
> >  
> >  void iommu_setup_dma_ops(struct device *dev)
> >  {
> > -	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> > +	struct iommu_domain *domain = iommu_get_domain_for_dev_locked(dev);
> 
> Lets have another patch to tidy this. This function can only be called on
> the default_domain. We can trivally pass it in. In all three cases the
> default domain was just attached to the device.

Will replace with your patch.

> > +/* Caller must be a general/external function that isn't an IOMMU callback */
> >  struct iommu_domain *iommu_get_domain_for_dev(struct device *dev)
> 
> Maybe a kdoc?
> 
> /**
>  * iommu_get_domain_for_dev() - Return the DMA API domain pointer
>  * @dev - Device to query
>  *
>  * This function can be called within a driver bound to dev. The returned
>  * pointer is valid for the lifetime of the bound driver.
>  *
>  * It should not be called by drivers with driver_managed_dma = true.
>  */
> struct iommu_domain *iommu_get_domain_for_dev(struct device *dev)

Will add this.

> I really wanted to say this should just always return the
> default_domain, but it looks like host1x_client_iommu_detach() is the
> only place outside the iommu drivers that would be unhappy with that.

I suppose any external user that allocates/attaches a domain has a
risk of potentially using this helper, in which case group->domain
may not be default_domain?

Thanks
Nicolin