linux-kernel - RE: [PATCH v2 00/10] Add IO page table replacement support

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Message-ID: <BN9PR11MB527636FD0A6CBC26AF344E378CDE9@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Fri, 10 Feb 2023 01:34:04 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Nicolin Chen <nicolinc@...dia.com>
CC:     "jgg@...dia.com" <jgg@...dia.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
Subject: RE: [PATCH v2 00/10] Add IO page table replacement support

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Friday, February 10, 2023 12:13 AM
> 
> On Thu, Feb 09, 2023 at 02:50:39AM +0000, Tian, Kevin wrote:
> > External email: Use caution opening links or attachments
> >
> >
> > > From: Nicolin Chen <nicolinc@...dia.com>
> > > Sent: Wednesday, February 8, 2023 5:18 AM
> > >
> > > QEMU with this feature should have the vIOMMU maintain a cache of the
> > > guest io page table addresses and assign a unique IOAS to each unique
> > > guest page table.
> > >
> >
> > I still didn't see a clear reply why above is required. Please elaborate.
> 
> Hmm..this piece was directly copied from Jason's inputs before I
> sent v1. And I thought he explained in the previous version. I
> can drop it in v3 if that makes you happy.
> 

Jason's reply was:

> I think the guidance is about the change to VFIO uAPI where it is now
> possible to change the domain attached, previously that was not
> possible

I cannot connect it to the above statement. Anyway if you think
that guidance to userspace is necessary please connect it to the
replace semantics to explain the motivation.