Re: [PATCH v4 07/16] x86/virt/tdx: Add tdx_alloc/free_page() helpers

[Edgecombe, Rick P]

On Thu, 2025-11-27 at 18:11 +0200, Nikolay Borisov wrote:
> > +/* Number PAMT pages to be provided to TDX module per 2M region of PA */
> > +static int tdx_dpamt_entry_pages(void)
> > +{
> > +	if (!tdx_supports_dynamic_pamt(&tdx_sysinfo))
> > +		return 0;
> > +
> > +	return tdx_sysinfo.tdmr.pamt_4k_entry_size * PTRS_PER_PTE /
> > PAGE_SIZE;
> > +}
> 
> Isn't this guaranteed to return 2 always as per the ABI? Can't the 
> allocation of the 2 pages be moved closer to where it's used - in 
> tdh_phymem_pamt_add which will simplify things a bit?

Yea, it could be simpler if it was always guaranteed to be 2 pages. But it was
my understanding that it would not be a fixed size. Can you point to what docs
makes you think that?

Another option would be to ask TDX folks to make it fixed, and then require an
opt-in for it to be expanded later if needed. I would have to check on them on
the reasoning for it being dynamic sized. I'm not sure if it is *that*
complicated at this point though. Once there is more than one, the loops becomes
tempting. And if we loop over 2 we could easily loop over n.