Re: [PATCH v3 6/6] x86/virt/tdx: Support DPAMT when adding memory for the extensions

["Edgecombe, Rick P" <rick.p.edgecombe@intel.com>]

On Thu, 2026-10-08 at 12:31 +0800, Xu Yilun wrote:
> > Since 511 out of 512 pages in each 2MB block will find the entry already
> > present, the newly allocated pages are immediately freed. For tens of
> > megabytes of extensions, this results in thousands of unnecessary
> > allocations
> > and frees. Furthermore, free_pamt_array() performs expensive memory resets,
> > leading to unnecessary boot delays.
> > 
> > Could a struct tdx_pamt_cache be allocated locally in tdx_ext_mem_setup()
> > and
> > passed into tdx_pamt_get() to avoid this thrashing?
> 
> tdx_pamt_cache is for cases where memory allocation is not possible when
> adding DPAMT. I don't think it's good to use tdx_pamt_cache in normal
> cases.

Since we are worrying about fragmented long term allocation of the actual pages
of this memory, it does seem valid to worry about the PAMT memory for the same
reason. But given the problem is 1/512 of the other one. Let's ignore it for
now.

For the excess alloc/free, yea, lets leave it for future optimization. We are
already doing some optimization ahead of time with the full page array
implementation.