[PATCH 2/2] arm64/mm: fix incorrect file_map_count for invalid pmd/pud

[Liu Shixin]

The page table check trigger BUG_ON() unexpectedly when split hugepage:

 ------------[ cut here ]------------
 kernel BUG at mm/page_table_check.c:119!
 Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
 Dumping ftrace buffer:
    (ftrace buffer empty)
 Modules linked in:
 CPU: 7 PID: 210 Comm: transhuge-stres Not tainted 6.1.0-rc3+ #748
 Hardware name: linux,dummy-virt (DT)
 pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
 pc : page_table_check_set.isra.0+0x398/0x468
 lr : page_table_check_set.isra.0+0x1c0/0x468
[...]
 Call trace:
  page_table_check_set.isra.0+0x398/0x468
  __page_table_check_pte_set+0x160/0x1c0
  __split_huge_pmd_locked+0x900/0x1648
  __split_huge_pmd+0x28c/0x3b8
  unmap_page_range+0x428/0x858
  unmap_single_vma+0xf4/0x1c8
  zap_page_range+0x2b0/0x410
  madvise_vma_behavior+0xc44/0xe78
  do_madvise+0x280/0x698
  __arm64_sys_madvise+0x90/0xe8
  invoke_syscall.constprop.0+0xdc/0x1d8
  do_el0_svc+0xf4/0x3f8
  el0_svc+0x58/0x120
  el0t_64_sync_handler+0xb8/0xc0
  el0t_64_sync+0x19c/0x1a0
[...]

On arm64, pmd_present() will return true even if the pmd is invalid. So
in pmdp_invalidate() the file_map_count will not only decrease once but
also increase once. Then in set_pte_at(), the file_map_count increase
again, and so trigger BUG_ON() unexpectedly.

Fix this problem by adding pmd_valid() in pmd_user_accessible_page().
Moreover, add pud_valid() for pud_user_accessible_page() too.

Fixes: 42b2547137f5 ("arm64/mm: enable ARCH_SUPPORTS_PAGE_TABLE_CHECK")
Reported-by: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
---
 arch/arm64/include/asm/pgtable.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index edf6625ce965..56e178de75e7 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -863,12 +863,12 @@ static inline bool pte_user_accessible_page(pte_t pte)
 
 static inline bool pmd_user_accessible_page(pmd_t pmd)
 {
-	return pmd_leaf(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd));
+	return pmd_leaf(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd)) && pmd_valid(pmd);
 }
 
 static inline bool pud_user_accessible_page(pud_t pud)
 {
-	return pud_leaf(pud) && pud_user(pud);
+	return pud_leaf(pud) && pud_user(pud) && pud_valid(pud);
 }
 #endif
 
-- 
2.25.1