Re: [PATCH v6 11/11] Documentation/x86: Add documentation for TDX's Dynamic PAMT

[Binbin Wu]

On 5/26/2026 10:35 AM, Rick Edgecombe wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> 
> Expand TDX documentation to include information on the Dynamic PAMT
> feature.
> 
> The new section explains PAMT support in the TDX module and how Dynamic
> PAMT affects the kernel memory use.
> 
> Assisted-by: Sashiko:claude-opus-4-6 GitHub Copilot:claude-opus-4-6 Claude:claude-opus-4-7
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Co-developed-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>

Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>

One nit below.

> ---
> v6:
>  - Add missing word (Binbin)
>  - Use "::" instead of ":"
>  - Make format of dmesg example accurate
> 
> v3:
>  - Trim down docs to be about things that user cares about, instead
>    of development history and other details like this.
> ---
>  Documentation/arch/x86/tdx.rst | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/Documentation/arch/x86/tdx.rst b/Documentation/arch/x86/tdx.rst
> index ff6b110291bc6..ce026a88b6f78 100644
> --- a/Documentation/arch/x86/tdx.rst
> +++ b/Documentation/arch/x86/tdx.rst
> @@ -73,6 +73,28 @@ initialize::
>  
>    [..] virt/tdx: TDX-Module initialization failed ...
>  
> +Dynamic PAMT
> +------------
> +
> +PAMT

Nit:
It seems that there is no spelling out of the acronym in the source code or the documentation.
Maybe it's a good place to give the full version. E.g.

Physical Address Metadata Table (PAMT) is ...

> is memory that the TDX module needs to keep data about each page
> +(think like struct page). It needs to be handed to the TDX module for its
> +exclusive use. For normal PAMT, this is installed when the TDX module
> +is first loaded and comes to about 0.4% of system memory.
> +
> +Dynamic PAMT is a TDX feature that allows VMM to allocate part of the
> +PAMT as needed (the parts for tracking 4KB size pages). The other page
> +sizes (1GB and 2MB) are still allocated statically at the time of
> +TDX module initialization. This reduces the amount of memory that TDX
> +uses while TDs are not in use.
> +
> +When Dynamic PAMT is in use, dmesg shows it like::
> +
> +  [..] virt/tdx: Enable Dynamic PAMT
> +  [..] virt/tdx: 10092 KB allocated for PAMT
> +  [..] virt/tdx: TDX-Module initialized
> +
> +Dynamic PAMT is enabled automatically if supported.
> +
>  TDX Interaction to Other Kernel Components
>  ------------------------------------------
>