linux-kernel - [PATCH v2 08/14] mm: copy_pte_range() use pte_offset_map_rw

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Message-Id: <71100c3867c4cf6f5f429ce9f2db8432066d0e99.1724310149.git.zhengqi.arch@bytedance.com>
Date: Thu, 22 Aug 2024 15:13:23 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: david@...hat.com,
	hughd@...gle.com,
	willy@...radead.org,
	muchun.song@...ux.dev,
	vbabka@...nel.org,
	akpm@...ux-foundation.org,
	rppt@...nel.org,
	vishal.moola@...il.com,
	peterx@...hat.com,
	ryan.roberts@....com,
	christophe.leroy2@...soprasteria.com
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH v2 08/14] mm: copy_pte_range() use pte_offset_map_rw_nolock()

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@...edance.com>
---
 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.
+	 */
+	src_pte = pte_offset_map_rw_nolock(src_mm, src_pmd, addr, &dummy_pmdval,
+					   &src_ptl);
 	if (!src_pte) {
 		pte_unmap_unlock(dst_pte, dst_ptl);
 		/* ret == 0 */
-- 
2.20.1