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

[Edgecombe, Rick P]

On Wed, 2026-07-08 at 17:13 +0800, Yan Zhao wrote:
> 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 ?

The text is trying to describe what PAMT is, so I'm not sure about this one.

> 
> > 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" ?

How about:
In Dynamic PAMT, only the 4KB page size backing 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." ?

The checking part is true, but is it needed to understand this patch? I think it
just needs a background of what is happening. How about:

So the kernel must install PAMT backing for any 4KB page being gifting to the
TDX module, and tear down the backing when the associated gifted pages are
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>
>