Re: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID_ALLOC/FREE

David Gibson
2021-10-01T06:30:46Z

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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.
> >
> > 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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