linux-kernel - RE: [PATCH v4 08/17] iommufd: Always setup MSI and anforce cc on kernel-managed domains

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Message-ID: <BN9PR11MB52763227866603ED7795AA068CD7A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Mon, 16 Oct 2023 08:48:03 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        Jason Gunthorpe <jgg@...dia.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>,
        "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>,
        "Martins, Joao" <joao.m.martins@...cle.com>
Subject: RE: [PATCH v4 08/17] iommufd: Always setup MSI and anforce cc on
 kernel-managed domains

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Saturday, October 14, 2023 8:45 AM
> 
> On Tue, Sep 26, 2023 at 01:16:35AM -0700, Tian, Kevin wrote:
> > > From: Liu, Yi L <yi.l.liu@...el.com>
> > > Sent: Thursday, September 21, 2023 3:51 PM
> > >
> > > From: Nicolin Chen <nicolinc@...dia.com>
> > >
> > > Now enforce_cache_coherency and msi_cookie are kernel-managed hwpt
> > > things.
> > > So, they should be only setup on kernel-managed domains. If the
> attaching
> > > domain is a user-managed domain, redirect the hwpt to hwpt->parent to
> do
> > > it correctly.
> > >
> >
> > No redirection. The parent should already have the configuration done
> > when it's created. It shouldn't be triggered in the nesting path.
> 
> iommufd_hw_pagetable_enforce_cc() is not only called in alloc(),
> but also in hwpt_attach/replace() if cc is not enforced by the
> alloc() because the idev that initiates the hwpt_alloc() might
> not have idev->enforce_cache_coherency. Only when another idev
> that has idev->enforce_cache_coherency attaches to the shared
> hwpt, the cc configuration would be done.
> 

is this a bug already? If the 1st device doesn't have enforce_cc in its
iommu, setting the snp bit in the hwpt would lead to reserved
bit violation.

another problem is that intel_iommu_enforce_cache_coherency()
doesn't update existing entries. It only sets a domain flag to affect
future mappings. so it means the 2nd idev is also broken.

The simplest option is to follow vfio type1 i.e. don't mix devices
with different enforce_cc in one domain.