linux-kernel - RE: [PATCH v1 0/8] Add IO page table replacement support

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Message-ID: <BN9PR11MB5276918F3FFF87555F84CD1F8CDB9@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Tue, 7 Feb 2023 00:34:47 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Nicolin Chen <nicolinc@...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 v1 0/8] Add IO page table replacement support

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Monday, February 6, 2023 9:26 PM
> 
> On Mon, Feb 06, 2023 at 06:39:29AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@...dia.com>
> > > Sent: Friday, February 3, 2023 11:04 PM
> > >
> > > On Fri, Feb 03, 2023 at 08:09:30AM +0000, Tian, Kevin wrote:
> > > > > From: Nicolin Chen <nicolinc@...dia.com>
> > > > > Sent: Thursday, February 2, 2023 3:05 PM
> > > > >
> > > > > 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 didn't get why we impose such requirement to userspace.
> > >
> > > I read this as implementation guidance for qemu. qemu can do what it
> > > wants of course
> > >
> >
> > sure but I still didn't get why this is a guidance specific to the
> > new replace cmd...
> 
> 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
> 

that is fine. I just didn't get why the original description emphasized
the cache and unique IOAS aspects in Qemu.