linux-kernel - RE: [RFC 06/20] iommu: Add iommu_device_init[exit]_user

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Message-ID: <BN9PR11MB543382131F4D3E9489766C698CA79@BN9PR11MB5433.namprd11.prod.outlook.com>
Date:   Mon, 27 Sep 2021 13:08:35 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "hch@....de" <hch@....de>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "lkml@...ux.net" <lkml@...ux.net>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "lushenming@...wei.com" <lushenming@...wei.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "corbet@....net" <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "yi.l.liu@...ux.intel.com" <yi.l.liu@...ux.intel.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>
Subject: RE: [RFC 06/20] iommu: Add iommu_device_init[exit]_user_dma
 interfaces

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Monday, September 27, 2021 7:34 PM
> 
> On 2021/9/27 17:42, Tian, Kevin wrote:
> > +int iommu_device_set_dma_hint(struct device *dev, enum dma_hint hint)
> > +{
> > +	struct iommu_group *group;
> > +	int ret;
> > +
> > +	group = iommu_group_get(dev);
> > +	/* not an iommu-probed device */
> > +	if (!group)
> > +		return 0;
> > +
> > +	mutex_lock(&group->mutex);
> > +	ret = __iommu_group_viable(group, hint);
> > +	mutex_unlock(&group->mutex);
> > +
> > +	iommu_group_put(group);
> > +	return ret;
> > +}
> 
> Conceptually, we could also move iommu_deferred_attach() from
> iommu_dma_ops here to save unnecessary checks in the hot DMA API
> paths?
> 

Yes, it's possible. But just be curious, why doesn't iommu core 
manage deferred_attach when receiving BOUND_DRIVER event?
Is there other implication that deferred attach cannot be done
at driver binding time?

Thanks
Kevin