Re: [RFC PATCH 19/34] x86: power: use proper set_pXd() for generic compile-time folded patable in resume_one_md_table_init()

> On 7/13/26 06:55, Yeoreum Yun wrote:
> > @@ -134,11 +129,12 @@ static inline void resume_init_first_level_page_table(pgd_t *pg_dir)
> >  {
> >  #ifdef CONFIG_X86_PAE
> >  	int i;
> > +	pud_t *pud = pud_offset(p4d_offset(pg_dir, 0), 0);
> >  
> >  	/* Init entries of the first-level page table to the zero page */
> >  	for (i = 0; i < PTRS_PER_PGD; i++)
> > -		set_pgd(pg_dir + i,
> > -			__pgd(__pa(empty_zero_page) | _PAGE_PRESENT));
> > +		set_pud(pud + i,
> > +			__pud(__pa(empty_zero_page) | _PAGE_PRESENT));
> >  #endif
> >  }
> 
> If this is the way forward, it's going to require the retraining of some
> awfully old brain cells.
> 
> It also doesn't really read correctly. Loop over each PGD entry:
> 
> 	for (i = 0; i < PTRS_PER_PGD; i++)
> 
> ... and set a pud?
> 
> 		set_pud(...)
> 
> I'm not sure how I'd ever learn the rules to write this code from
> scratch. Right now, the code says: "The pgd_t is the top level of the
> page tables. I know there are PTRS_PER_PGD of those top level entries
> entries I need to 'zero'."
> 
> You don't have to know what is folded, just that you're dealing with the
> top level.
> 
> But *this* code says:
> 
> 1. The pgd_t is the top level of the page tables. Start there.
> 2. "Walk" down *two* (folded) levels
> 3. Set the third-level (pud) entries to 'zero'
> 
> So the code now *has* to know how the folding occurs.
> 
> This seems really hard to work with to me.

Actually, This is what the patch series want.
IOW, the "code" need to consider the folded pgtable level and
use a proper APIs.

Might for the clarification, change a PTRS_PER_PGD to PTRS_PER_PUD
seems better. but the using set_pgd() seems much more worse since
second argument type is p4d_t which doesn't exist in the p4d folded case.

IOW, this patch wants to use proper API for the real first page table
level. for example, X86_PAE's pgtable level is 3 so not use pgd friends function
but use a pud to setup first page table entries.

-- 
Sincerely,
Yeoreum Yun