linux-kernel - Re: [PATCH v3 06/17] iommufd: Only enforce IOMMU_RESV_SW

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Date:   Fri, 28 Jul 2023 14:06:56 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>
Subject: Re: [PATCH v3 06/17] iommufd: Only enforce IOMMU_RESV_SW_MSI when
 attaching user-managed HWPT

On Fri, Jul 28, 2023 at 10:02:36AM +0000, Tian, Kevin wrote:
> > From: Liu, Yi L <yi.l.liu@...el.com>
> > Sent: Monday, July 24, 2023 7:04 PM
> >  	}
> > 
> >  	rc = iopt_table_enforce_dev_resv_regions(&hwpt->ioas->iopt, idev-
> > >dev,
> > -						 &idev->igroup-
> > >sw_msi_start);
> > +						 &idev->igroup-
> > >sw_msi_start,
> > +						 !!hwpt->parent);
> >  	if (rc)
> >  		goto err_unlock;
> 
> I prefer to not setting parent ioas to hwpt in iommufd_hw_pagetable_alloc().

Yes, the prior patch didn't add it to the iopt, so it shouldn't have
an ioas set. The NESTED domains don't have an IOAS almost by
definition.

> then here ioas can be retrieved from hwpt->parent and then it'd be pretty
> clear that in nested case the sw_msi reservation happens in the parent
> instead of pretending the stage-1 hwpt has an ioas too.

Yeah, I'm confused by this patch as well.  Since there should be no
IOAS for the NESTED why are we messing with resv_regions?

Jason