Re: [PATCH v2 4/4] coco/tdx-host: Initialize trusted DMA on all capable IOMMUs

[Baolu Lu <baolu.lu@linux.intel.com>]

On 10/22/2026 12:07 PM, Tian, Kevin wrote:
>> From: Baolu Lu<baolu.lu@linux.intel.com>
>> Sent: Monday, October 19, 2026 4:12 PM
>>
>> On 10/16/2026 3:17 PM, Tian, Kevin wrote:
>>>>     - The TDX Connect architecture places requirements on the host
>>>>       iommu driver while the secure IOMMU is being set up. For example,
>>>>       the host iommu driver must block the enhanced command (ECMD)
>>>>       interface while the TDH.IOMMU.SETUP SEAMCALL runs, and it must
>>>>       reserve the upper half of the domain ID space. These steps have
>>>>       to happen atomically under the iommu driver's own locks. As a
>>>>       result, the Intel iommu driver needs to merge the two steps above
>>>>       into one.
>>> Didn't get this. Both ECMD and DID reservation are TDX specific things.
>>> How are they related to the two steps in the ARM sides and why calls
>>> for merging?
>>>
>>> and why are they must be done atomically? they are conditions to
>>> execute TDH.IOMMU.SETUP, but it is perfectly fine to reserve DID
>>> at an early point then block ECMD later...
>> You are right, "atomically" was too strong. Only the ECMD block has to
>> bracket TDH.IOMMU.SETUP. So I plan to restructure it as follows:
>>
>> - dmar_tdxcs_init_prepare(dev, &params): resolve the device's DRHD and
>>     take a reference on its secure-mode state. For the first user,
>>     validate the preconditions (TE/QI/SM enabled), reserve the upper half
>>     of the DID space (failing with -EBUSY if any of it is in use), block
>>     ECMD and return what tdx-host needs (register base, NUMA node, etc).
>>     If the unit is already in Secure TDX mode, just report that so
>>     tdx-host skips TDH.IOMMU.SETUP.
>>
>> - dmar_tdxcs_init_done(dev, result): unblock ECMD, then either mark the
>>     unit as being in Secure TDX mode or roll back (including the DID
>>     reservation), based on the SEAMCALL result. It must be called
>>     whenever init_prepare() returns success.
> We should continue blocking ECMD after the IOMMU successfully
> enters the TDX mode.

Updated.

Thanks,
baolu