Re: [Xen-devel] [PATCH v5 02/15] iommu: introduce the concept of BFN...

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Paul Durrant [mailto:paul.durrant@xxxxxxxxxx]
> Sent: Saturday, August 4, 2018 1:22 AM
> 
> ...meaning 'bus frame number' i.e. a frame number mapped in the IOMMU
> rather than the MMU.
> 
> This patch is a largely cosmetic change that substitutes the terms 'gfn'
> and 'gaddr' for 'bfn' and 'baddr' in all the places where the frame number
> or address relate to the IOMMU rather than the MMU.
> 
> The parts that are not purely cosmetic are:
> 
>  - the introduction of a type-safe declaration of bfn_t and definition of
>    INVALID_BFN to make the substitution of gfn_x(INVALID_GFN) mechanical.
>  - the introduction of __bfn_to_baddr and __baddr_to_bfn (and type-safe
>    variants without the leading __) with some use of the former.
> 
> Subsequent patches will convert code to make use of type-safe BFNs.
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>

[...]

> diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
> index 24654e8e22..4ebf91f17e 100644
> --- a/xen/include/xen/mm.h
> +++ b/xen/include/xen/mm.h
> @@ -14,8 +14,9 @@
>   * should be adhered to.
>   *
>   * mfn: Machine Frame Number
> - *   The values Xen puts into its own pagetables.  This is the host physical
> - *   memory address space with RAM, MMIO etc.
> + *   The values Xen puts into its own pagetables, 2nd stage pagetables
> (where
> + *   hardware assisted 2nd stage translation is used) or IOMMU page
> tables.
> + *   This is the host physical memory address space with RAM, MMIO etc.

there is also shadow page table... not sure whether it is really helpful
to list all of them out. "Xen-owned pagetables" should be sufficient to cover.

>   *
>   * gfn: Guest Frame Number
>   *   The values a guest puts in its own pagetables.  For an auto-translated
> @@ -26,6 +27,11 @@
>   *   A linear idea of a guest physical address space. For an auto-translated
>   *   guest, pfn == gfn while for a non-translated guest, pfn != gfn.
>   *
> + * bfn: Bus Frame Number (definitions in include/xen/iommu.h)
> + *   The linear frame numbers of IOMMU address space. All initiators for a
> + *   given domain share a single IOMMU address space and, by default,
> Xen will
> + *   ensure bfn == pfn.
> + *

Above description is a bit confusing:

- for 'domain', are you talking about VM or IOMMU domain? If the former
then each initiator could have its own IOMMU address space when a virtual
IOMMU (either pvIOMMU or emulated IOMMU) is exposed.

- since you talk about 'by default', better also talk about non-default case,
i.e. when virtual IOMMU is exposed then bfn is a separate address space
managed by guest

>   * WARNING: Some of these terms have changed over time while others
> have been
>   * used inconsistently, meaning that a lot of existing code does not match
> the
>   * definitions above.  New code should use these terms as described here,
> and
> --
> 2.11.0


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