Re: [PATCH v6 07/11] KVM: TDX: Allocate PAMT memory for TD and vCPU control structures

[Yan Zhao]

On Mon, May 25, 2026 at 07:35:11PM -0700, Rick Edgecombe wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> 
> Use control page helpers for allocating and freeing TD control structures,
> such these operations can work for Dynamic PAMT.
> 
> The TDX module tracks some state for each page of physical memory that it
> might use. It calls this state the PAMT. It includes separate state for
Nit: It records this state in the PAMT ?

> each page size a physical page could be utilized at within the TDX module
> (1GB, 2MB, 4KB). In Dynamic PAMT, only the 4KB page size state is
> allocated dynamically. So the kernel must install PAMT backing for each 4KB
How about
"..., only the backend to hold the 4KB page size state is allocated
dynamically" ?

> page before gifting it to the TDX module, and tear it down after the page
> is reclaimed.
How about
"So the kernel must check whether it is necessary to install/remove PAMT
backing for each 4KB page, and do so when necessary before gifting the page
to the TDX module or after it is reclaimed." ?

> TD-scoped control pages (TDR, TDCS) and vCPU-scoped control pages (TDVPR,
> TDCX) are all handed to the TDX module at 4KB page size and are therefore
> subject to this requirement. Replace the raw alloc_page()/__free_page()
> calls for these pages with tdx_alloc/free_control_page().
> 
> Switching between special Dynamic PAMT operations or normal page
> alloc/free operations is handled internally in
> tdx_alloc/free_control_page(). So don't check for Dynamic PAMT around these
> calls. Just call them unconditionally. Similarly, drop the NULL checks
> before freeing, as tdx_free_control_page() handles NULL internally.
> 
> No functional change intended when Dynamic PAMT is not in use.

Reviewed-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>