Re: [PATCH v6 02/11] x86/virt/tdx: Allocate page bitmap for Dynamic PAMT

[Chao Gao]

On Mon, May 25, 2026 at 07:35:06PM -0700, Rick Edgecombe 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. At a high level, Dynamic PAMT still has the 1GB and 2MB
>levels allocated on TDX module initialization, but the 4KB level is
>allocated dynamically during runtime.
>
>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 regular 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 regular, non-dynamic 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.
>
>Unlike the existing metadata reading code, this code is not generated by a
>script. So adjust the comment to be more generic. Also, start to adopt a
>more normal kernel code style without the tenary statements and if
>conditionals assignments that the auto generated code has.
>
>Assisted-by: Sashiko:claude-opus-4-6
>Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
>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: Chao Gao <chao.gao@xxxxxxxxx>