linux-kernel - RE: [PATCH v3 07/17] iommufd: Add IOMMU_RESV_IOVA

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Message-ID: <BN9PR11MB527633F9EFD1EFB52772CD158C08A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Thu, 3 Aug 2023 01:25:37 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Nicolin Chen <nicolinc@...dia.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>
Subject: RE: [PATCH v3 07/17] iommufd: Add IOMMU_RESV_IOVA_RANGES

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Thursday, August 3, 2023 9:23 AM
> 
> On Wed, Aug 02, 2023 at 01:09:28AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@...dia.com>
> > > Sent: Wednesday, August 2, 2023 2:23 AM
> > >
> > > On Tue, Aug 01, 2023 at 02:40:44AM +0000, Tian, Kevin wrote:
> > >
> > > > > So, I guess we should leave it like this?
> > > > >
> > > >
> > > > Yes. Along with this discussion (including what you explained for
> sw_msi)
> > > > let's abandon this new cmd and leave it as today.
> > >
> > > You sure? This makes it basically impossible to write a "correct" vmm
> > > that is aware of what the physical memory map must be early on
> > >
> >
> > emmm... I thought it's what you meant by "leave it like this" and the
> > fact that existing VMM's memory layout happens to match the reserved
> > regions. Nobody complains lacking of such a interface for years then
> > we may postpone supporting it until it's really required.
> >
> > btw even if we add this new cmd now, getting the Qemu support to
> > use the aggregated list when creating the guest memory map is not
> > a simple task given currently vfio only passively acts on change
> > notifications in the guest memory layout. It requires a new mechanism
> > to enforce strict order (probe all vfio devices before creating the memory
> > layout) and then injects vfio reserved regions into the layout.
> >
> > Preferably let's not making it a hard dependency for this series.
> 
> Should we drop this and its selftest patch from this series?
> 

Yes. let's drop it.