diff mbox series

[v3,11/14] mm: userfaultfd: move_pages_pte() use pte_offset_map_rw_nolock()

Message ID 20240904084022.32728-12-zhengqi.arch@bytedance.com (mailing list archive)
State Handled Elsewhere
Headers show
Series introduce pte_offset_map_{ro|rw}_nolock() | expand

Commit Message

Qi Zheng Sept. 4, 2024, 8:40 a.m. UTC 
In move_pages_pte(), we may modify the dst_pte and src_pte after acquiring
the ptl, so convert it to using pte_offset_map_rw_nolock(). But since we
already do the pte_same() check, 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@bytedance.com>
---
 mm/userfaultfd.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

Comments

Muchun Song Sept. 5, 2024, 12:20 p.m. UTC | #1 
> On Sep 4, 2024, at 16:40, Qi Zheng <zhengqi.arch@bytedance.com> wrote:
> 
> In move_pages_pte(), we may modify the dst_pte and src_pte after acquiring
> the ptl, so convert it to using pte_offset_map_rw_nolock(). But since we
> already do the pte_same() check, 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@bytedance.com>

Reviewed-by: Muchun Song <muchun.song@linux.dev>

Thanks.
diff mbox series

Patch

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index ce13c40626472..48b87c62fc3dd 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1135,7 +1135,7 @@  static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,
 	spinlock_t *src_ptl, *dst_ptl;
 	pte_t *src_pte = NULL;
 	pte_t *dst_pte = NULL;
-
+	pmd_t dummy_pmdval;
 	struct folio *src_folio = NULL;
 	struct anon_vma *src_anon_vma = NULL;
 	struct mmu_notifier_range range;
@@ -1146,7 +1146,14 @@  static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,
 				src_addr, src_addr + PAGE_SIZE);
 	mmu_notifier_invalidate_range_start(&range);
 retry:
-	dst_pte = pte_offset_map_nolock(mm, dst_pmd, dst_addr, &dst_ptl);
+	/*
+	 * Use the maywrite version to indicate that dst_pte will be modified,
+	 * but since we will use pte_same() to detect the change of the pte
+	 * entry, there is no need to get pmdval, so just pass a dummy variable
+	 * to it.
+	 */
+	dst_pte = pte_offset_map_rw_nolock(mm, dst_pmd, dst_addr, &dummy_pmdval,
+					   &dst_ptl);
 
 	/* Retry if a huge pmd materialized from under us */
 	if (unlikely(!dst_pte)) {
@@ -1154,7 +1161,9 @@  static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,
 		goto out;
 	}
 
-	src_pte = pte_offset_map_nolock(mm, src_pmd, src_addr, &src_ptl);
+	/* same as dst_pte */
+	src_pte = pte_offset_map_rw_nolock(mm, src_pmd, src_addr, &dummy_pmdval,
+					   &src_ptl);
 
 	/*
 	 * We held the mmap_lock for reading so MADV_DONTNEED