Re: [PATCH v1 4/5] mm: ptdump: Support hugepd table entries

[Christophe Leroy]

Hi Daniel,

Le 16/04/2021 à 01:29, Daniel Axtens a écrit :
> Hi Christophe,
>
> > Which hugepd, page table entries can be at any level
> > and can be of any size.
> >
> > Add support for them.
> >
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> > ---
> >   mm/ptdump.c | 17 +++++++++++++++--
> >   1 file changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/ptdump.c b/mm/ptdump.c
> > index 61cd16afb1c8..6efdb8c15a7d 100644
> > --- a/mm/ptdump.c
> > +++ b/mm/ptdump.c
> > @@ -112,11 +112,24 @@ static int ptdump_pte_entry(pte_t *pte, unsigned long addr,
> >   {
> >   	struct ptdump_state *st = walk->private;
> >   	pte_t val = ptep_get(pte);
> > +	unsigned long page_size = next - addr;
> > +	int level;
> > +
> > +	if (page_size >= PGDIR_SIZE)
> > +		level = 0;
> > +	else if (page_size >= P4D_SIZE)
> > +		level = 1;
> > +	else if (page_size >= PUD_SIZE)
> > +		level = 2;
> > +	else if (page_size >= PMD_SIZE)
> > +		level = 3;
> > +	else
> > +		level = 4;
> >   
> >   	if (st->effective_prot)
> > -		st->effective_prot(st, 4, pte_val(val));
> > +		st->effective_prot(st, level, pte_val(val));
> >   
> > -	st->note_page(st, addr, 4, pte_val(val), PAGE_SIZE);
> > +	st->note_page(st, addr, level, pte_val(val), page_size);
>
> It seems to me that passing both level and page_size is a bit redundant,
> but I guess it does reduce the impact on each arch's code?

Exactly, as shown above, the level can be re-calculated based on the page size, but it would be a 
unnecessary impact on all architectures and would duplicate the re-calculation of the level whereas 
in most cases we get it for free from the caller.

> Kind regards,
> Daniel
>
> >   
> >   	return 0;
> >   }
> > --
> > 2.25.0