Re: [Qemu-devel] [PATCH-for-4.2 v3 2/5] memory: Add IOMMU_ATTR_VFIO_NESTED IOMMU memory region attribute

[Peter Maydell]

On Thu, 11 Jul 2019 at 07:19, Eric Auger <address@hidden> wrote:
>
> We introduce a new IOMMU Memory Region attribute,
> IOMMU_ATTR_VFIO_NESTED that tells whether the virtual IOMMU
> requires HW nested paging for VFIO integration.
>
> Current Intel virtual IOMMU device supports "Caching
> Mode" and does not require 2 stages at physical level to be
> integrated with VFIO. However SMMUv3 does not implement such
> "caching mode" and requires to use HW nested paging.
>
> As such SMMUv3 is the first IOMMU device to advertise this
> attribute.

I'm not sure the name of the attribute really captures
the intention here, though I don't have any better
suggestions. Maybe IOMMU_ATTR_VFIO_NEEDS_HW_NESTED_PAGING ?

> Signed-off-by: Eric Auger <address@hidden>
> ---
>  hw/arm/smmuv3.c       | 12 ++++++++++++
>  include/exec/memory.h |  3 ++-
>  2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/hw/arm/smmuv3.c b/hw/arm/smmuv3.c
> index e96d5beb9a..384c02cb91 100644
> --- a/hw/arm/smmuv3.c
> +++ b/hw/arm/smmuv3.c
> @@ -1490,6 +1490,17 @@ static void 
> smmuv3_notify_flag_changed(IOMMUMemoryRegion *iommu,
>      }
>  }
>
> +static int smmuv3_get_attr(IOMMUMemoryRegion *iommu,
> +                           enum IOMMUMemoryRegionAttr attr,
> +                           void *data)
> +{
> +    if (attr == IOMMU_ATTR_VFIO_NESTED) {
> +        *(bool *) data = true;

I'm surprised checkpatch doesn't warn about the space after
the cast here.

> +        return 0;
> +    }
> +    return -EINVAL;
> +}
> +
>  static void smmuv3_iommu_memory_region_class_init(ObjectClass *klass,
>                                                    void *data)
>  {
> @@ -1497,6 +1508,7 @@ static void 
> smmuv3_iommu_memory_region_class_init(ObjectClass *klass,
>
>      imrc->translate = smmuv3_translate;
>      imrc->notify_flag_changed = smmuv3_notify_flag_changed;
> +    imrc->get_attr = smmuv3_get_attr;
>  }
>
>  static const TypeInfo smmuv3_type_info = {
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index a078cd033f..e477a630a8 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -204,7 +204,8 @@ struct MemoryRegionOps {
>  };
>
>  enum IOMMUMemoryRegionAttr {
> -    IOMMU_ATTR_SPAPR_TCE_FD
> +    IOMMU_ATTR_SPAPR_TCE_FD,
> +    IOMMU_ATTR_VFIO_NESTED,
>  };

Could we have a comment documenting what the attribute's meaning
and semantics are, please? (including what the type is that the
data pointer is expected to point to, ie 'bool'.)

(We ought also to document the spapr-specific attribute...)

thanks
-- PMM