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Date:   Fri, 1 Oct 2021 16:13:58 +1000
From:   David Gibson <david@gibson.dropbear.id.au>
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Liu Yi L <yi.l.liu@intel.com>, alex.williamson@redhat.com,
        hch@lst.de, jasowang@redhat.com, joro@8bytes.org,
        jean-philippe@linaro.org, kevin.tian@intel.com, parav@mellanox.com,
        lkml@metux.net, pbonzini@redhat.com, lushenming@huawei.com,
        eric.auger@redhat.com, corbet@lwn.net, ashok.raj@intel.com,
        yi.l.liu@linux.intel.com, jun.j.tian@intel.com, hao.wu@intel.com,
        dave.jiang@intel.com, jacob.jun.pan@linux.intel.com,
        kwankhede@nvidia.com, robin.murphy@arm.com, kvm@vger.kernel.org,
        iommu@lists.linux-foundation.org, dwmw2@infradead.org,
        linux-kernel@vger.kernel.org, baolu.lu@linux.intel.com,
        nicolinc@nvidia.com
Subject: Re: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID_ALLOC/FREE
Message-ID: <YVanJqG2pt6g+ROL@yekko>
References: <20210919063848.1476776-1-yi.l.liu@intel.com>
 <20210919063848.1476776-12-yi.l.liu@intel.com>
 <20210921174438.GW327412@nvidia.com>
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On Tue, Sep 21, 2021 at 02:44:38PM -0300, Jason Gunthorpe wrote:
> 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.
> >=20
> > 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 point,
> > as the false setting requires additional contract with KVM on handling
> > WBINVD emulation, which can be added later.
> >=20
> > Userspace is expected to call IOMMU_CHECK_EXTENSION (see next patch)
> > for what formats can be specified when allocating an IOASID.
> >=20
> > Open:
> > - Devices on PPC platform currently use a different iommu driver in vfi=
o.
> >   Per previous discussion they can also use vfio type1v2 as long as the=
re
> >   is a way to claim a specific iova range from a system-wide address sp=
ace.
> >   This requirement doesn't sound PPC specific, as addr_width for pci de=
vices
> >   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 discu=
ssion
> >   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
> actual geometry including any holes via a query.

So part of the point of specifying start/end addresses is that
explicitly querying holes shouldn't be necessary: if the requested
range crosses a hole, it should fail.  If you didn't really need all
that range, you shouldn't have asked for it.

Which means these aren't really "hints" but optionally supplied
constraints.

--=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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