[PATCH v5 2/6] userfaultfd: use kmap_local_page() in copy_huge_page_from_user()

Peng Zhang
2023-03-31T09:42:07Z

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

diff --git a/mm/memory.c b/mm/memory.c
index 387226d6094d..808f354bce65 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5880,16 +5880,14 @@ 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