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

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Date:   Fri, 1 Oct 2021 09:25:05 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "hch@....de" <hch@....de>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "lkml@...ux.net" <lkml@...ux.net>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "lushenming@...wei.com" <lushenming@...wei.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "corbet@....net" <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "yi.l.liu@...ux.intel.com" <yi.l.liu@...ux.intel.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>
Subject: Re: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID_ALLOC/FREE

On Fri, Oct 01, 2021 at 04:19:22PM +1000, david@...son.dropbear.id.au wrote:
> 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@...dia.com>
> > > > Sent: Wednesday, September 22, 2021 1:45 AM
> > > > 
> > > > 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
> > > 
> > > is the hint single-range or could be multiple-ranges?
> > 
> > David explained it here:
> > 
> > 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.

As I understood your remarks each IOAS can only be one of the formats
as they have a different PTE layout. So here I ment that qmeu needs to
be able to pick *for each IOAS* which of the two formats it is.

> 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.

And this would result in two different IOAS objects

Jason