On 2024/8/29 23:36, David Hildenbrand wrote:
On 22.08.24 09:13, Qi Zheng wrote:
In copy_pte_range(), we may modify the src_pte entry after holding the
src_ptl, so convert it to using pte_offset_map_rw_nolock(). But since we
already hold the write lock of mmap_lock, there is no need to get pmdval
to do pmd_same() check, just pass a dummy variable to it.
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
mm/memory.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/mm/memory.c b/mm/memory.c
index 7b6071a0e21e2..30d98025b2a40 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1083,6 +1083,7 @@ copy_pte_range(struct vm_area_struct *dst_vma,
struct vm_area_struct *src_vma,
struct mm_struct *src_mm = src_vma->vm_mm;
pte_t *orig_src_pte, *orig_dst_pte;
pte_t *src_pte, *dst_pte;
+ pmd_t dummy_pmdval;
pte_t ptent;
spinlock_t *src_ptl, *dst_ptl;
int progress, max_nr, ret = 0;
@@ -1108,7 +1109,15 @@ copy_pte_range(struct vm_area_struct *dst_vma,
struct vm_area_struct *src_vma,
ret = -ENOMEM;
goto out;
}
- src_pte = pte_offset_map_nolock(src_mm, src_pmd, addr, &src_ptl);
+
+ /*
+ * Use the maywrite version to indicate that dst_pte will be
modified,
+ * but since we already hold the write lock of mmap_lock, there
is no
+ * need to get pmdval to do pmd_same() check, just pass a dummy
variable
+ * to it.
As we hold the mmap lock write lock, I assume it will prevent any page
table removal, because they need *at least* the mmap lock in read mode,
right?
Except for retract_page_tables(), all others hold the read lock of
mmap_lock.
We should probably document the rules for removing a page table -- which
locks must be held in which mode (if not already done).
Agree, I will document it in the v3.
