Re: [PATCH v4 23/24] x86/virt/tdx: Document TDX Module updates

[Huang, Kai]

On Thu, 2026-02-12 at 06:35 -0800, Chao Gao wrote:
> Document TDX Module updates as a subsection of "TDX Host Kernel Support" to
> provide background information and cover key points that developers and
> users may need to know, for example:
> 
>  - update is done in stop_machine() context
>  - update instructions and results
>  - update policy and tooling
> 
> Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
> ---
>  Documentation/arch/x86/tdx.rst | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/Documentation/arch/x86/tdx.rst b/Documentation/arch/x86/tdx.rst
> index 61670e7df2f7..01ae560c7f66 100644
> --- a/Documentation/arch/x86/tdx.rst
> +++ b/Documentation/arch/x86/tdx.rst
> @@ -99,6 +99,40 @@ initialize::
>  
>    [..] virt/tdx: module initialization failed ...
>  
> +TDX Module Runtime Updates
> +--------------------------
> +
> +The TDX architecture includes a persistent SEAM loader (P-SEAMLDR) that
> +runs in SEAM mode separately from the TDX Module. The kernel can
> +communicate with P-SEAMLDR to perform runtime updates of the TDX Module.
> +
> +During updates, the TDX Module becomes unresponsive to other TDX
> +operations. To prevent components using TDX (such as KVM) from experiencing
> +unexpected errors during updates, updates are performed in stop_machine()
> +context.

During "updates" or "update"?  The module only becomes unresponsive during
"one module runtime update", correct?

> +
> +TDX Module updates have complex compatibility requirements; the new module
> +must be compatible with the current CPU, P-SEAMLDR, and running TDX Module.
> +Rather than implementing complex module selection and policy enforcement
> +logic in the kernel, userspace is responsible for auditing and selecting
> +appropriate updates.
> +
> +Updates use the standard firmware upload interface. See
> +Documentation/driver-api/firmware/fw_upload.rst for detailed instructions
> +
> +Successful updates are logged in dmesg:
> +  [..] virt/tdx: version 1.5.20 -> 1.5.24
> +
> +If updates failed, running TDs may be killed and further TDX operations may
> +be not possible until reboot. For detailed error information, see
> +Documentation/ABI/testing/sysfs-devices-faux-tdx-host.
> +
> +Given the risk of losing existing TDs, userspace should verify that the update
> +is compatible with the current system and properly validated before applying it.
> +A reference userspace tool that implements necessary checks is available at:
> +
> +  https://github.com/intel/confidential-computing.tdx.tdx-module.binaries
> +
>  TDX Interaction to Other Kernel Components
>  ------------------------------------------
>  

I think I've confused what you mean by "updates" or "update".

Perhaps you mean the "steps" during module update as "updates"?

But to me you indeed said "update" in the changelog:

"
 - update is done in stop_machine() context
 - update instructions and results
 - update policy and tooling
"

Please make this consistent at least.

With this clarified/addressed, feel free to add:

Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>