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

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Message-ID: <ZMpKmgPAuQDI2nDx@nvidia.com>
Date:   Wed, 2 Aug 2023 09:22:50 -0300
From:   Jason Gunthorpe <jgg@...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>,
        "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>,
        "nicolinc@...dia.com" <nicolinc@...dia.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

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.

I see, if qemu won't use it then lets not do it

Jason