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?
We should probably document the rules for removing a page table -- which locks must be held in which mode (if not already done).
-- Cheers, David / dhildenb
