Re: [PATCH v9 02/11] x86/virt/tdx: Allocate page bitmap for Dynamic PAMT

[Vishal Annapurve]

On Wed, Aug 5, 2026 at 7:09 PM Rick Edgecombe
<rick.p.edgecombe@xxxxxxxxx> wrote:
>
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
>
> The TDX Physical Address Metadata Table (PAMT) holds data about the
> physical memory used by TDX, and must be allocated by the kernel during
> TDX module initialization.
>
> The exact size of the required PAMT memory is determined by the TDX module
> and may vary between TDX module versions. Currently it is approximately
> 0.4% of the system memory. This is a significant commitment, especially if
> it is not known upfront whether the machine will run any TDX guests.
>
> Each memory region that the TDX module might use needs three separate PAMT
> allocations. One for each supported page size (1GB, 2MB, 4KB). The
> TDX module supports a new feature designed to reduce PAMT overhead called
> Dynamic PAMT. Under Dynamic PAMT the 4KB level is allocated dynamically
> during runtime, while the 1GB and 2MB levels remain allocated on TDX
> module initialization.
>
> However, in the details, Dynamic PAMT still needs some smaller per 4KB
> page scoped data (currently it is 1 bit per page). The TDX module exposes
> the number of bits as a separate piece of metadata than the 4KB static
> allocation for normal PAMT. Although the size is enumerated differently,
> it is handed to the TDX module in the same way the 4KB page size PAMT
> allocation is for normal PAMT.
>
> Begin to implement Dynamic PAMT in the kernel by reading the bits-per-page
> needed for Dynamic PAMT. Calculate the size needed for the bitmap,
> and use it instead of the 4KB size determined for normal PAMT, in the case
> of Dynamic PAMT.
>
> The existing metadata reading code was generated by a script, but the
> current plan is to stop generating this code, as the script has continued
> to need adjustments. So add manually written code and adjust the comment
> about it being autogenerated to be more generic. Start to adopt a more
> normal kernel code style without the ternary statements and if
> conditionals assignments that the auto generated code has.
>
> AI was used under supervision to collect/apply feedback, review code and
> workshop logs.
>
> 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>
> Tested-by: Hongyu Ning <hongyu.ning@xxxxxxxxxxxxxxx>
> Reviewed-by: Vishal Annapurve <vannapurve@xxxxxxxxxx>
> Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
> Reviewed-by: Tony Lindgren <tony.lindgren@xxxxxxxxxxxxxxx>
> Reviewed-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> Acked-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>
> ---

Reviewed-by: Vishal Annapurve <vannapurve@xxxxxxxxxx>