Re: [PATCH v2 0/8] Initial support for SMMUv3 nested translation

Zhangfei Gao
2024-10-16T02:25:49Z

Hi, Jason

On Tue, 27 Aug 2024 at 23:51, Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> This brings support for the IOMMFD ioctls:
>
> - IOMMU_GET_HW_INFO
> - IOMMU_HWPT_ALLOC_NEST_PARENT
> - IOMMU_DOMAIN_NESTED
> - ops->enforce_cache_coherency()
>
> This is quite straightforward as the nested STE can just be built in the
> special NESTED domain op and fed through the generic update machinery.
>
> The design allows the user provided STE fragment to control several
> aspects of the translation, including putting the STE into a "virtual
> bypass" or a aborting state. This duplicates functionality available by
> other means, but it allows trivially preserving the VMID in the STE as we
> eventually move towards the VIOMMU owning the VMID.
>
> Nesting support requires the system to either support S2FWB or the
> stronger CANWBS ACPI flag. This is to ensure the VM cannot bypass the
> cache and view incoherent data, currently VFIO lacks any cache flushing
> that would make this safe.

What if the system does not support S2FWB or CANWBS, any workaround to
passthrough?
Currently I am testing nesting by ignoring this check.

Thanks