Re: [PATCH v5 03/22] coco/tdx-host: Expose TDX module version

[Kiryl Shutsemau <kas@kernel.org>]

On Sun, Mar 15, 2026 at 06:58:23AM -0700, Chao Gao wrote:
> For TDX module updates, userspace needs to select compatible update
> versions based on the current module version. This design delegates
> module selection complexity to userspace because TDX module update
> policies are complex and version series are platform-specific.
> 
> For example, the 1.5.x series is for certain platform generations, while
> the 2.0.x series is intended for others. And TDX module 1.5.x may be
> updated to 1.5.y but not to 1.5.y+1.
> 
> Expose the TDX module version to userspace via sysfs to aid module
> selection. Since the TDX faux device will drive module updates, expose
> the version as its attribute.
> 
> One bonus of exposing TDX module version via sysfs is: TDX module
> version information remains available even after dmesg logs are cleared.
> 
> == Background ==
> 
> The "faux device + device attribute" approach compares to other update
> mechanisms as follows:
> 
> 1. AMD SEV leverages an existing PCI device for the PSP to expose
>    metadata. TDX uses a faux device as it doesn't have PCI device
>    in its architecture.
> 
> 2. Microcode uses per-CPU virtual devices to report microcode revisions
>    because CPUs can have different revisions. But, there is only a
>    single TDX module, so exposing the TDX module version through a global
>    TDX faux device is appropriate
> 
> 3. ARM's CCA implementation isn't in-tree yet, but will likely follow a
>    similar faux device approach, though it's unclear whether they need
>    to expose firmware version information
> 
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
> Reviewed-by: Tony Lindgren <tony.lindgren@linux.intel.com>
> Reviewed-by: Xu Yilun <yilun.xu@linux.intel.com>
> Link: https://lore.kernel.org/all/2025073035-bulginess-rematch-b92e@gregkh/ # [1]

Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov