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SubjectRe: [PATCH v1 3/5] mm: ptdump: Provide page size to notepage()
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On 15/04/2021 18:18, Christophe Leroy wrote:
> In order to support large pages on powerpc, notepage()
> needs to know the page size of the page.
>
> Add a page_size argument to notepage().
>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
> arch/arm64/mm/ptdump.c | 2 +-
> arch/riscv/mm/ptdump.c | 2 +-
> arch/s390/mm/dump_pagetables.c | 3 ++-
> arch/x86/mm/dump_pagetables.c | 2 +-
> include/linux/ptdump.h | 2 +-
> mm/ptdump.c | 16 ++++++++--------
> 6 files changed, 14 insertions(+), 13 deletions(-)
>
[...]
> diff --git a/mm/ptdump.c b/mm/ptdump.c
> index da751448d0e4..61cd16afb1c8 100644
> --- a/mm/ptdump.c
> +++ b/mm/ptdump.c
> @@ -17,7 +17,7 @@ static inline int note_kasan_page_table(struct mm_walk *walk,
> {
> struct ptdump_state *st = walk->private;
>
> - st->note_page(st, addr, 4, pte_val(kasan_early_shadow_pte[0]));
> + st->note_page(st, addr, 4, pte_val(kasan_early_shadow_pte[0]), PAGE_SIZE);

I'm not completely sure what the page_size is going to be used for, but
note that KASAN presents an interesting case here. We short-cut by
detecting it's a KASAN region at a high level (PGD/P4D/PUD/PMD) and
instead of walking the tree down just call note_page() *once* but with
level==4 because we know KASAN sets up the page table like that.

However the one call actually covers a much larger region - so while
PAGE_SIZE matches the level it doesn't match the region covered. AFAICT
this will lead to odd results if you enable KASAN on powerpc.

To be honest I don't fully understand why powerpc requires the page_size
- it appears to be using it purely to find "holes" in the calls to
note_page(), but I haven't worked out why such holes would occur.

Steve

>
> walk->action = ACTION_CONTINUE;
>
> @@ -41,7 +41,7 @@ static int ptdump_pgd_entry(pgd_t *pgd, unsigned long addr,
> st->effective_prot(st, 0, pgd_val(val));
>
> if (pgd_leaf(val))
> - st->note_page(st, addr, 0, pgd_val(val));
> + st->note_page(st, addr, 0, pgd_val(val), PGDIR_SIZE);
>
> return 0;
> }
> @@ -62,7 +62,7 @@ static int ptdump_p4d_entry(p4d_t *p4d, unsigned long addr,
> st->effective_prot(st, 1, p4d_val(val));
>
> if (p4d_leaf(val))
> - st->note_page(st, addr, 1, p4d_val(val));
> + st->note_page(st, addr, 1, p4d_val(val), P4D_SIZE);
>
> return 0;
> }
> @@ -83,7 +83,7 @@ static int ptdump_pud_entry(pud_t *pud, unsigned long addr,
> st->effective_prot(st, 2, pud_val(val));
>
> if (pud_leaf(val))
> - st->note_page(st, addr, 2, pud_val(val));
> + st->note_page(st, addr, 2, pud_val(val), PUD_SIZE);
>
> return 0;
> }
> @@ -102,7 +102,7 @@ static int ptdump_pmd_entry(pmd_t *pmd, unsigned long addr,
> if (st->effective_prot)
> st->effective_prot(st, 3, pmd_val(val));
> if (pmd_leaf(val))
> - st->note_page(st, addr, 3, pmd_val(val));
> + st->note_page(st, addr, 3, pmd_val(val), PMD_SIZE);
>
> return 0;
> }
> @@ -116,7 +116,7 @@ static int ptdump_pte_entry(pte_t *pte, unsigned long addr,
> if (st->effective_prot)
> st->effective_prot(st, 4, pte_val(val));
>
> - st->note_page(st, addr, 4, pte_val(val));
> + st->note_page(st, addr, 4, pte_val(val), PAGE_SIZE);
>
> return 0;
> }
> @@ -126,7 +126,7 @@ static int ptdump_hole(unsigned long addr, unsigned long next,
> {
> struct ptdump_state *st = walk->private;
>
> - st->note_page(st, addr, depth, 0);
> + st->note_page(st, addr, depth, 0, 0);
>
> return 0;
> }
> @@ -153,5 +153,5 @@ void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm, pgd_t *pgd)
> mmap_read_unlock(mm);
>
> /* Flush out the last page */
> - st->note_page(st, 0, -1, 0);
> + st->note_page(st, 0, -1, 0, 0);
> }
>

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