linux-kernel - Re: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID

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Message-ID: <YVanJqG2pt6g+ROL@yekko>
Date:   Fri, 1 Oct 2021 16:13:58 +1000
From:   David Gibson <david@...son.dropbear.id.au>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Liu Yi L <yi.l.liu@...el.com>, alex.williamson@...hat.com,
        hch@....de, jasowang@...hat.com, joro@...tes.org,
        jean-philippe@...aro.org, kevin.tian@...el.com, parav@...lanox.com,
        lkml@...ux.net, pbonzini@...hat.com, lushenming@...wei.com,
        eric.auger@...hat.com, corbet@....net, ashok.raj@...el.com,
        yi.l.liu@...ux.intel.com, jun.j.tian@...el.com, hao.wu@...el.com,
        dave.jiang@...el.com, jacob.jun.pan@...ux.intel.com,
        kwankhede@...dia.com, robin.murphy@....com, kvm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, dwmw2@...radead.org,
        linux-kernel@...r.kernel.org, baolu.lu@...ux.intel.com,
        nicolinc@...dia.com
Subject: Re: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID_ALLOC/FREE

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.
> > 
> > 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.
> > 
> > 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 address 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.
> 
> 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.

-- 
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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