[PATCH v16 13/25] mm: pagewalk: Don't lock PTEs for walk_page_range_novma()

Steven Price
2019-12-06T13:54:27Z

walk_page_range_novma() can be used to walk page tables or the kernel or
for firmware. These page tables may contain entries that are not backed
by a struct page and so it isn't (in general) possible to take the PTE
lock for the pte_entry() callback. So update walk_pte_range() to only
take the lock when no_vma==false and add a comment explaining the
difference to walk_page_range_novma().

Signed-off-by: Steven Price <steven.price@arm.com>
---
mm/pagewalk.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index efa464cf079b..1b9a3ba24c51 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -10,9 +10,10 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
pte_t *pte;
int err = 0;
const struct mm_walk_ops *ops = walk->ops;
- spinlock_t *ptl;
+ spinlock_t *uninitialized_var(ptl);

- pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
+ pte = walk->no_vma ? pte_offset_map(pmd, addr) :
+ pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
for (;;) {
err = ops->pte_entry(pte, addr, addr + PAGE_SIZE, walk);
if (err)
@@ -23,7 +24,9 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
pte++;
}

- pte_unmap_unlock(pte, ptl);
+ if (!walk->no_vma)
+ spin_unlock(ptl);
+ pte_unmap(pte);
return err;
}

@@ -383,6 +386,12 @@ int walk_page_range(struct mm_struct *mm, unsigned long start,
return err;
}

+/*
+ * Similar to walk_page_range() but can walk any page tables even if they are
+ * not backed by VMAs. Because 'unusual' entries may be walked this function
+ * will also not lock the PTEs for the pte_entry() callback. This is useful for
+ * walking the kernel pages tables or page tables for firmware.
+ */
int walk_page_range_novma(struct mm_struct *mm, unsigned long start,
unsigned long end, const struct mm_walk_ops *ops,
void *private)
--
2.20.1