Re: [PATCH v3 5/6] x86/virt/tdx: Re-initialize the extensions on runtime TDX module update

[Tony Lindgren <tony.lindgren@linux.intel.com>]

On Tue, Oct 06, 2026 at 01:41:49AM +0800, Xu Yilun wrote:
> Runtime TDX module update introduces a mechanism to update the module
> firmware while preserving and restoring TDX operations. The extensions
> functionalities should also be re-initialized as part of the restoration
> process.
> 
> The TDX architecture supports an update flow which allows updated
> extensions to consume more memory than their original boot-time
> requirement. So the arch defines the extensions re-initialization flow
> the same as boot-up initialization: the host queries TDX module how much
> additional memory needed, allocates it, adds it to the module via
> TDH.EXT.MEM.ADD, then re-initializes the extensions via TDH.EXT.INIT.
> 
> Linux runs the updates in stop_machine() context, which prevents memory
> allocation. So for Linux, a compatible update must not install updated
> extensions that require additional memory.
> 
> Given that the memory for the extensions must not increase, the
> re-initialization skips the memory adding steps. It is simplified as:
> 
>   - Check if the extensions are supported via TDX_FEATURES0_EXT. If not,
>     skip the extensions re-initialization.
> 
>   - Re-initialize the extensions via TDH.EXT.INIT. The SEAMCALL leaf
>     will fail if the updated extensions require more memory, which
>     indicates the update image is not compatible.

Reviewed-by: Tony Lindgren <tony.lindgren@linux.intel.com>