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Date:   Fri, 1 Oct 2021 16:19:22 +1000
From:   "david@gibson.dropbear.id.au" <david@gibson.dropbear.id.au>
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     "Tian, Kevin" <kevin.tian@intel.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        "alex.williamson@redhat.com" <alex.williamson@redhat.com>,
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        "corbet@lwn.net" <corbet@lwn.net>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "yi.l.liu@linux.intel.com" <yi.l.liu@linux.intel.com>,
        "Tian, Jun J" <jun.j.tian@intel.com>, "Wu, Hao" <hao.wu@intel.com>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        "jacob.jun.pan@linux.intel.com" <jacob.jun.pan@linux.intel.com>,
        "kwankhede@nvidia.com" <kwankhede@nvidia.com>,
        "robin.murphy@arm.com" <robin.murphy@arm.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
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        "baolu.lu@linux.intel.com" <baolu.lu@linux.intel.com>,
        "nicolinc@nvidia.com" <nicolinc@nvidia.com>
Subject: Re: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID_ALLOC/FREE
Message-ID: <YVaoamAaqayk1Hja@yekko>
References: <20210919063848.1476776-1-yi.l.liu@intel.com>
 <20210919063848.1476776-12-yi.l.liu@intel.com>
 <20210921174438.GW327412@nvidia.com>
 <BN9PR11MB543362CEBDAD02DA9F06D8ED8CA29@BN9PR11MB5433.namprd11.prod.outlook.com>
 <20210922140911.GT327412@nvidia.com>
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On Wed, Sep 22, 2021 at 11:09:11AM -0300, Jason Gunthorpe wrote:
> On Wed, Sep 22, 2021 at 03:40:25AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > Sent: Wednesday, September 22, 2021 1:45 AM
> > >=20
> > > On Sun, Sep 19, 2021 at 02:38:39PM +0800, Liu Yi L wrote:
> > > > This patch adds IOASID allocation/free interface per iommufd. When
> > > > allocating an IOASID, userspace is expected to specify the type and
> > > > format information for the target I/O page table.
> > > >
> > > > This RFC supports only one type (IOMMU_IOASID_TYPE_KERNEL_TYPE1V2),
> > > > implying a kernel-managed I/O page table with vfio type1v2 mapping
> > > > semantics. For this type the user should specify the addr_width of
> > > > the I/O address space and whether the I/O page table is created in
> > > > an iommu enfore_snoop format. enforce_snoop must be true at this po=
int,
> > > > as the false setting requires additional contract with KVM on handl=
ing
> > > > WBINVD emulation, which can be added later.
> > > >
> > > > Userspace is expected to call IOMMU_CHECK_EXTENSION (see next patch)
> > > > for what formats can be specified when allocating an IOASID.
> > > >
> > > > Open:
> > > > - Devices on PPC platform currently use a different iommu driver in=
 vfio.
> > > >   Per previous discussion they can also use vfio type1v2 as long as=
 there
> > > >   is a way to claim a specific iova range from a system-wide addres=
s space.
> > > >   This requirement doesn't sound PPC specific, as addr_width for pci
> > > devices
> > > >   can be also represented by a range [0, 2^addr_width-1]. This RFC =
hasn't
> > > >   adopted this design yet. We hope to have formal alignment in v1
> > > discussion
> > > >   and then decide how to incorporate it in v2.
> > >=20
> > > I think the request was to include a start/end IO address hint when
> > > creating the ios. When the kernel creates it then it can return the
> >=20
> > is the hint single-range or could be multiple-ranges?
>=20
> David explained it here:
>=20
> https://lore.kernel.org/kvm/YMrKksUeNW%2FPEGPM@yekko/

Apparently not well enough.  I've attempted again in this thread.

> qeumu needs to be able to chooose if it gets the 32 bit range or 64
> bit range.

No. qemu needs to supply *both* the 32-bit and 64-bit range to its
guest, and therefore needs to request both from the host.

Or rather, it *might* need to supply both.  It will supply just the
32-bit range by default, but the guest can request the 64-bit range
and/or remove and resize the 32-bit range via hypercall interfaces.
Vaguely recent Linux guests certainly will request the 64-bit range in
addition to the default 32-bit range.

--=20
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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