Re: [PATCHv2 02/12] x86/virt/tdx: Allocate page bitmap for Dynamic PAMT

[Huang, Kai]

On Thu, 2025-07-31 at 01:06 +0000, Edgecombe, Rick P wrote:
> On Wed, 2025-06-25 at 11:06 -0700, Dave Hansen wrote:
> > This is the wrong place to do this.
> > 
> > Hide it in tdmr_get_pamt_sz(). Don't inject it in the main code flow
> > here and complicate the for loop.
> 
> I'm finding this tdmr_get_pamt_sz() maybe too strange to build on top of. 
> It iterates through these special TDX page sizes once, and calls into 
> tdmr_get_pamt_sz() for each, which in turn has a case statement for each 
> index. So the loop doesn't add much - each index still has its own line 
> of code inside tdmr_get_pamt_sz(). And then despite prepping the base/size 
> in an array via the loop, it has to be packed manually at the end for each 
> index. So I'm not sure if the general wisdom of doing things in a single way 
> is really adding much here.
> 
> I'm wondering if something like the below might be a better base to build 
> on. For dpamt the "tdmr->pamt_4k_size =" line could just branch on 
> tdx_supports_dynamic_pamt(). Any thoughts on it as an alternative to the 
> suggestion to add the dpamt logic to tdmr_get_pamt_sz()?

The code change LGTM, albeit I am not sure whether it is definitely
better.

For where to add dynamic PAMT logic, I think it's reasonable to put such
logic into tdmr_get_pamt_sz() because it changes the amount of memory that
we need to allocate for 4K page size.  If we do dynamic PAMT logic at
higher level, the code logic in tdmr_get_pamt_sz() to calculate PAMT size
for 4K page will not be accurate, i.e., it is only correct w/o dynamic
PAMT.