Hi Yeoreum,
On Tue, 14 Jul 2026 at 18:51, Yeoreum Yun <[email protected]> wrote:
> On Tue, Jul 14, 2026 at 05:08:24PM +0100, Yeoreum Yun wrote:
> > On Tue, Jul 14, 2026 at 07:35:19AM -0700, Dave Hansen wrote:
> > > On 7/14/26 04:40, Yeoreum Yun wrote:
> > > > @@ -254,22 +255,8 @@ static void effective_prot(struct ptdump_state
> > > > *pt_st, int level, u64 val)
> > > > struct pg_state *st = container_of(pt_st, struct pg_state,
> > > > ptdump);
> > > > pgprotval_t prot = val & PTE_FLAGS_MASK;
> > > > pgprotval_t effective;
> > > > - bool first_level = false;
> > > >
> > > > - /* Ignore folded levels ... */
> > > > - if (((level == 0) && mm_p4d_folded(st->mm)) ||
> > > > - ((level == 1) && mm_pud_folded(st->mm)) ||
> > > > - ((level == 2) && mm_pmd_folded(st->mm)))
> > > > - return;
> > > > -
> > > > - /* ... and make the actual first level remember the protection.
> > > > */
> > > > - if (((level == 0)) ||
> > > > - ((level == 1) && mm_p4d_folded(st->mm)) ||
> > > > - ((level == 2) && mm_pud_folded(st->mm)) ||
> > > > - ((level == 3) && mm_pmd_folded(st->mm)))
> > > > - first_level = true;
> > > > -
> > > > - if (!first_level) {
> > > > + if (first_level > st->first_level) {
> > > > pgprotval_t higher_prot = st->prot_levels[level - 1];
> > > >
> > > > effective = (higher_prot & prot & (_PAGE_USER |
> > > > _PAGE_RW)) |
> > > > @@ -471,6 +458,15 @@ bool ptdump_walk_pgd_level_core(struct seq_file *m,
> > > > .seq = m
> > > > };
> > > >
> > > > + if (mm_pmd_folded (mm))
> > > > + st->first_level = 3;
> > > > + else if (mm_pud_folded (mm))
> > > > + st->first_level = 2;
> > > > + else if (mm_p4d_folded (mm))
> > > > + st->first_level = 1;
> > > > + else
> > > > + st->first_level = 0;
> > > > +
> > > > ptdump_walk_pgd(&st.ptdump, mm, pgd);
> > >
> > > This is indeed an improvement and a step in the right direction! Thanks
> > > for looking at this.
> > >
> > > But one of my test for whether it's good x86 code is whether there's any
> > > actually x86-specific logic in it. Isn't this basically a translation
> > > between the integer level number and whether it is folded?
> > >
> > > That seems like a common helper that more than one arch could use. Could
> > > this be stuck in a helper so that all arch/x86 has to do is:
> > >
> > > if (mm_pt_level_folded(mm, level))
> > > return;
> >
> > Yes. at least the level semantic in ptdump (pgd is level 0,
> > p4d is level 1, ...) is same to all archs where use ptdump.
> > So It seems reasonable to add this common helper in ptdump.c
> >
>
> Furthermore, the effective_prot() need to require to identify whether
> it's the first pgtable to prevent the inheriting from dummy value.
> So I think it seems to make a ptdump_pt_level_first() like:
>
> diff --git a/mm/ptdump.c b/mm/ptdump.c
> index 973020000096c..2ec5700e4be5e 100644
> --- a/mm/ptdump.c
> +++ b/mm/ptdump.c
> @@ -190,6 +190,23 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct
> mm_struct *mm, pgd_t *pgd)
> st->note_page_flush(st);
> }
>
> +bool pdtump_pt_level_first(struct mm_struct *mm, int level)
> +{
> + if (!mm || level > CONFIG_PGTABLE_LEVELS)
> + return false;
> +
> + if (mm_pmd_folded(mm) && level == 3)
> + return true;
> + if (mm_pud_folded(mm) && level == 2)
> + return true;
> + if (mm_p4d_folded(mm) && level == 1)
> + return true;
Is this order (... && level == ...) the optimal order?
On arm64, mm_pud_folded() and mm_p4d_folded() perform several checks.
> + if (level == 0)
> + return true;
> +
> + return false;
> +}
>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
