linux-kernel - [PATCH v4 2/6] userfaultfd: use kmap_local_page() in copy_huge_page_from

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Date:   Thu, 30 Mar 2023 21:40:41 +0800
From:   Peng Zhang <zhangpeng362@...wei.com>
To:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <akpm@...ux-foundation.org>, <willy@...radead.org>,
        <mike.kravetz@...cle.com>
CC:     <vishal.moola@...il.com>, <muchun.song@...ux.dev>,
        <sidhartha.kumar@...cle.com>, <wangkefeng.wang@...wei.com>,
        <sunnanyong@...wei.com>, ZhangPeng <zhangpeng362@...wei.com>
Subject: [PATCH v4 2/6] userfaultfd: use kmap_local_page() in copy_huge_page_from_user()

From: ZhangPeng <zhangpeng362@...wei.com>

kmap() and kmap_atomic() are being deprecated in favor of
kmap_local_page() which is appropriate for any thread local context.[1]

Let's replace the kmap() and kmap_atomic() with kmap_local_page() in
copy_huge_page_from_user(). When allow_pagefault is false, disable page
faults to prevent potential deadlock.[2]

[1] https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com/
[2] https://lkml.kernel.org/r/20221025220136.2366143-1-ira.weiny@intel.com

Signed-off-by: ZhangPeng <zhangpeng362@...wei.com>
---
 mm/memory.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index f77fccb5310c..c47b8991410a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5866,16 +5866,14 @@ long copy_huge_page_from_user(struct page *dst_page,
 
 	for (i = 0; i < pages_per_huge_page; i++) {
 		subpage = nth_page(dst_page, i);
-		if (allow_pagefault)
-			page_kaddr = kmap(subpage);
-		else
-			page_kaddr = kmap_atomic(subpage);
+		page_kaddr = kmap_local_page(subpage);
+		if (!allow_pagefault)
+			pagefault_disable();
 		rc = copy_from_user(page_kaddr,
 				usr_src + i * PAGE_SIZE, PAGE_SIZE);
-		if (allow_pagefault)
-			kunmap(subpage);
-		else
-			kunmap_atomic(page_kaddr);
+		if (!allow_pagefault)
+			pagefault_enable();
+		kunmap_local(page_kaddr);
 
 		ret_val -= (PAGE_SIZE - rc);
 		if (rc)
-- 
2.25.1