Re: [PATCH v4 16/16] Documentation/x86: Add documentation for TDX's Dynamic PAMT

[Binbin Wu <binbin.wu@linux.intel.com>]

On 11/21/2025 8:51 AM, Rick Edgecombe wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> 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.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> [Add feedback, update log]
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> ---
> 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 | 21 +++++++++++++++++++++
>   1 file changed, 21 insertions(+)
>
> diff --git a/Documentation/arch/x86/tdx.rst b/Documentation/arch/x86/tdx.rst
> index 61670e7df2f7..8d45d31fee29 100644
> --- a/Documentation/arch/x86/tdx.rst
> +++ b/Documentation/arch/x86/tdx.rst
> @@ -99,6 +99,27 @@ initialize::
>   
>     [..] virt/tdx: module initialization failed ...
>   
> +Dynamic PAMT
> +------------
> +
> +PAMT is memory that the TDX module needs to keep data about each page
> +(think like struct page). It needs to handed to the TDX module for its
                                         ^
                                         be
> +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: module initialized
> +
> +Dynamic PAMT is enabled automatically if supported.
> +
>   TDX Interaction to Other Kernel Components
>   ------------------------------------------
>