Re: [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@xxxxxxxxxx>
---
  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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