On Tue, 10 May 2022 13:55:24 -0300
Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
> This control causes the ARM SMMU drivers to choose a stage 2
> implementation for the IO pagetable (vs the stage 1 usual default),
> however this choice has no visible impact to the VFIO user. Further qemu
> never implemented this and no other userspace user is known.
>
> The original description in commit f5c9ecebaf2a ("vfio/iommu_type1: add
> new VFIO_TYPE1_NESTING_IOMMU IOMMU type") suggested this was to "provide
> SMMU translation services to the guest operating system" however the rest
> of the API to set the guest table pointer for the stage 1 was never
> completed, or at least never upstreamed, rendering this part useless dead
> code.
>
> Since the current patches to enable nested translation, aka userspace page
> tables, rely on iommufd and will not use the enable_nesting()
> iommu_domain_op, remove this infrastructure. However, don't cut too deep
> into the SMMU drivers for now expecting the iommufd work to pick it up -
> we still need to create S2 IO page tables.
>
> Remove VFIO_TYPE1_NESTING_IOMMU and everything under it including the
> enable_nesting iommu_domain_op.
>
> Just in-case there is some userspace using this continue to treat
> requesting it as a NOP, but do not advertise support any more.
>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> ---
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 16 ----------------
> drivers/iommu/arm/arm-smmu/arm-smmu.c | 16 ----------------
> drivers/iommu/iommu.c | 10 ----------
> drivers/vfio/vfio_iommu_type1.c | 12 +-----------
> include/linux/iommu.h | 3 ---
> include/uapi/linux/vfio.h | 2 +-
> 6 files changed, 2 insertions(+), 57 deletions(-)
>
> It would probably make sense for this to go through the VFIO tree with Robin's
> ack for the SMMU changes.
I'd be in favor of applying this, but it seems Robin and Eric are
looking for a stay of execution and I'd also be looking for an ack from
Joerg. Thanks,
Alex
