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

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Message-ID: <ZSnkiKoCspmG1+/j@Asurada-Nvidia>
Date:   Fri, 13 Oct 2023 17:44:56 -0700
From:   Nicolin Chen <nicolinc@...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>,
        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

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.

In a nesting case encountering the same situation above, the S2
hwpt is allocated without the iommufd_hw_pagetable_enforce_cc().
But the 2nd idev that has idev->enforce_cache_coherency might
attach directly to the S1 domain/hwpt without touching the S2
domain (for the same VM, S2 domain can be shared). In this case,
without a redirection, the iommufd_hw_pagetable_enforce_cc()
would be missed.

Any thought?

Nic