> On 7/22/26 23:00, Yeoreum Yun wrote:
> > On Wed, Jul 22, 2026 at 01:20:39PM -0700, Dave Hansen wrote:
> >> On 7/22/26 10:37, Yeoreum Yun wrote:
> >>> However, mm_pXd_folded() requires to mm for other architecture like
> >>> s390. might save the mm instead of first_level and calls the
> >>> ptdump_pt_level_first() with static inline version would make the
> >>> constant comparison. So it requires to save *mm* structure in here.
> >>
> >> I'm having a really hard time parsing that.
> >>
> >> I think you're trying to say that the effective_prot_p*() functions need
> >> to know the first level but they don't (today) need the mm_struct. If
> >> they don't get the (calculated) first_level passed in, they need the
> >> mm_struct instead.
> >>
> >> I think you're arguing 'pg_state' needs a ->first_level or a ->mm.
> >> Having a pg_state->mm doesn't seem bad to me at all.
> >>
> >> But, it's also a little bit silly. It would not be rocket science to
> >> pass an mm_struct down to the effective_prot_p*() functions. It makes a
> >> whole lot of sense to me for a page table walking function to need
> >> metadata from the mm_struct to walk correctly.
> >
> > Yes. I mean to add pg_state->mm like:
> >
> > diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
> > index 2afa7a23340e..aaf00f0c6624 100644
> > --- a/arch/x86/mm/dump_pagetables.c
> > +++ b/arch/x86/mm/dump_pagetables.c
> > @@ -38,6 +38,7 @@ struct pg_state {
> > bool check_wx;
> > unsigned long wx_pages;
> > struct seq_file *seq;
> > + struct mm_struct *mm;
> > };
> >
> > struct addr_marker {
> > @@ -254,7 +255,7 @@ static void effective_prot(struct ptdump_state *pt_st,
> > int level, u64 val)
> > pgprotval_t prot = val & PTE_FLAGS_MASK;
> > pgprotval_t effective;
> >
> > - if (level > 0) {
> > + if (level > pgtable_first_level(st->mm)) {
> > pgprotval_t higher_prot = st->prot_levels[level - 1];
> >
> > effective = (higher_prot & prot & (_PAGE_USER | _PAGE_RW)) |
> > @@ -452,7 +453,8 @@ bool ptdump_walk_pgd_level_core(struct seq_file *m,
> > .level = -1,
> > .to_dmesg = dmesg,
> > .check_wx = checkwx,
> > - .seq = m
> > + .seq = m,
> > + .mm = mm,
> > };
> >
> > ptdump_walk_pgd(&st.ptdump, mm, pgd);
> > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> > index 8c093c119e5a..6e7d0580db99 100644
> > --- a/include/linux/pgtable.h
> > +++ b/include/linux/pgtable.h
> > @@ -2490,4 +2490,15 @@ pgprot_t vm_get_page_prot(vm_flags_t vm_flags)
> > \
> > } \
> > EXPORT_SYMBOL(vm_get_page_prot);
> >
> > +static inline int pgtable_first_level(struct mm_struct *mm)
> > +{
> > + if (mm_pmd_folded(mm))
> > + return 3;
> > + if (mm_pud_folded(mm))
> > + return 2;
> > + if (mm_p4d_folded(mm))
> > + return 1;
> > + return 0;
> > +}
>
> In that case the function should probably be called
>
> "mm_first_pgtable_level"
>
> But now it gets confusing, because we have
>
> enum pgtable_level {
> PGTABLE_LEVEL_PTE = 0,
> PGTABLE_LEVEL_PMD,
> PGTABLE_LEVEL_PUD,
> PGTABLE_LEVEL_P4D,
> PGTABLE_LEVEL_PGD,
> };
>
>
> But maybe we can make sense of it and do
>
> /*
> * The enum values correspond to the numerical page table level,
> * starting with the highest level being level 0.
> */
> enum pgtable_level {
> PGTABLE_LEVEL_PGD = 0,
> PGTABLE_LEVEL_P4D,
> PGTABLE_LEVEL_PUD,
> PGTABLE_LEVEL_PMD,
> PGTABLE_LEVEL_PTE,
> };
>
> static inline enum pgtable_level mm_first_pgtable_level(struct mm_struct *mm)
> {
> if (mm_pmd_folded(mm))
> return PGTABLE_LEVEL_PMD;
> if (mm_pud_folded(mm))
> return PGTABLE_LEVEL_PUD;
> if (mm_p4d_folded(mm))
> return PGTABLE_LEVEL_P4D;
> return PGTABLE_LEVEL_PGD;
> }
>
>
> We could even teach effective_prot() and friends to consume enum pgtable_level
> now and have it all be a bit cleaner?
Yes. That would be good for me unless others comment.
--
Sincerely,
Yeoreum Yun
