Re: [PATCH] iommu/amd: Add Secure ATS support

[Yi Liu <yi.l.liu@intel.com>]

On 2025/2/25 18:58, Vasant Hegde wrote:
> AMD IOMMU supports processing ATS requests as Secure ATS requests when IOTLB
> is supported and enabled (See section "2.11 Secure ATS Supports" in AMD IOMMU
> spec [1] for more detail).

glad to see it. I'm also working on Secure ATS for VT-d. Intel Secure ATS
has an extra table named HPT (Host Permission Table) chapter 4.2.4 in
revision 5.0 spec. IOMMU uses this table to check the address in the
translated transactions to ensure the device has access permission.

We plan to support the HPT on S2 when nested translation is configured. But
we may let the userspace VMM to decide if it wants SATS on specific device.
The reason is that some devices might be considered as trusted. e.g.
integrated devices.

My thought is to add a flag in iommufd_hw_capabilities to report the
capability, and add a flag in iommufd_hwpt_alloc_flags to let iommu driver
know if HPT is needed when allocating S2 domain. Userspace attaches the
un-trusted devices to the domains with HPT. While trusted devices can be
attached to 'normal' S2 domains.  Will to send it out soon.:)

> With Secure ATS, for ATS requests IOMMU return GPA to device instead of SPA.

I suppose AMD Secure ATS only works under nested translation configuration.
is it? I guess admin may want some flexibility to opt-in it. :)

-- 
Regards,
Yi Liu