Re: [Qemu-arm] [PATCH v4 2/5] memory: Add IOMMU_ATTR_HW_NESTED_PAGING IOMMU memory region attribute

[Peter Maydell]

On Thu, 22 Aug 2019 at 18:24, Eric Auger <address@hidden> wrote:
>
> We introduce a new IOMMU Memory Region attribute,
> IOMMU_ATTR_HW_NESTED_PAGING that tells whether the virtual
> IOMMU relies on physical IOMMU HW nested paging capability
> when protecting host assigned devices.

I'm still not really happy with the name of this attribute.
"IOMMU_ATTR_HW_NESTED_PAGING" sounds like it ought to mean
"true if this IOMMU supports/is using hardware nested paging". What
your commit message suggests it means is "true if this IOMMU
*needs* hardware nested paging", but there's no NEEDS in the
attribute name.

> 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.
>
> Signed-off-by: Eric Auger <address@hidden>

The code changes look good to me though.

thanks
-- PMM