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

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Date:   Mon, 23 Oct 2023 11:42:36 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
CC:     Jason Gunthorpe <jgg@...dia.com>, "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>,
        "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 Mon, Oct 23, 2023 at 02:53:20AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@...dia.com>
> > Sent: Monday, October 23, 2023 8:18 AM
> >
> > On Sat, Oct 21, 2023 at 01:38:04PM -0300, Jason Gunthorpe wrote:
> > > On Fri, Oct 20, 2023 at 11:59:13AM -0700, Nicolin Chen wrote:
> > > > On Fri, Oct 20, 2023 at 10:55:01AM -0300, Jason Gunthorpe wrote:
> > > > > On Fri, Oct 20, 2023 at 02:43:58AM +0000, Tian, Kevin wrote:
> > > > >
> > > > > > But the user shouldn't assume such explicit consistency since it's not
> > > > > > defined in our uAPI. All we defined is that the attaching may
> > > > > > fail due to incompatibility for whatever reason then the user can
> > > > > > always try creating a new hwpt for the to-be-attached device. From
> > > > > > this regard I don't see providing consistency of result is
> > > > > > necessary. 😊
> > > > >
> > > > > Anyhow, OK, lets add a comment summarizing your points and remove
> > the
> > > > > cc upgrade at attach time (sorry Nicolin/Yi!)
> > > >
> > > > Ack. I will send a small removal series. I assume it should CC
> > > > stable tree also?
> > >
> > > No, it seems more like tidying that fixing a functional issue, do I
> > > misunderstand?
> >
> > Hmm. Maybe the misunderstanding is mine -- Kevin was asking if
> > it was already a bug and you answered yes:
> > https://lore.kernel.org/linux-iommu/20231016115736.GP3952@nvidia.com/
> >
> 
> currently intel-iommu driver already rejects 1) enforcing CC on
> a domain which is already attached to non-CC device and
> 2) attaching a non-CC device to a domain which has enforce_cc.
> 
> so there is no explorable bug to fix in stable tree.

I see. Thanks!