Re: [PATCH v9 01/11] x86/virt/tdx: Simplify PAMT layout calculation

[Vishal Annapurve]

On Wed, Aug 5, 2026 at 7:09 PM Rick Edgecombe
<rick.p.edgecombe@xxxxxxxxx> wrote:
>
> For each memory region that the TDX module might use (called TDMR), three
> separate traditional PAMT allocations are needed. There is one for each
> supported page size (1GB, 2MB, 4KB). These store information on each page
> in the TDMR. In Linux, they are allocated out of one physically contiguous
> block, in order to more efficiently use some internal TDX module
> bookkeeping resources. So some simple math is needed to break the single
> large allocation into three smaller allocations for each page size.
>
> There are some commonalities in the math needed to calculate the base and
> size for each smaller allocation, and so an effort was made to share logic
> across the three. Unfortunately doing this turned out unnaturally tortured,
> with a loop iterating over the three page sizes, only to call into a
> function with case statements for each page size. In the future Dynamic
> PAMT will add more logic that is special to the 4KB page size, making the
> benefit of the math sharing even more questionable.
>
> Three is not a very high number, so get rid of the loop and just duplicate
> the small calculation three times. In doing so, setup for future Dynamic
> PAMT changes.
>
> Since the loop that iterates over it is gone, further simplify the code by
> dropping the array of intermediate size and base storage. Just store the
> values to their final locations.
>
> AI was used under supervision to collect/apply feedback, review code and
> workshop logs.
>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> Tested-by: Hongyu Ning <hongyu.ning@xxxxxxxxxxxxxxx>
> Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
> Reviewed-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
> Reviewed-by: Chao Gao <chao.gao@xxxxxxxxx>
> Reviewed-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> Reviewed-by: Tony Lindgren <tony.lindgren@xxxxxxxxxxxxxxx>
> Acked-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>

Reviewed-by: Vishal Annapurve <vannapurve@xxxxxxxxxx>