[PATCH v5 3/7] mm: hugetlb: fix missing cache flush in copy_huge_page_from_user()

[Muchun Song]

The userfaultfd calls copy_huge_page_from_user() which does not do
any cache flushing for the target page.  Then the target page will
be mapped to the user space with a different address (user address),
which might have an alias issue with the kernel address used to copy
the data from the user to.  Fix this issue by flushing dcache in
copy_huge_page_from_user().

Fixes: fa4d75c1de13 ("userfaultfd: hugetlbfs: add copy_huge_page_from_user for hugetlb userfaultfd support")
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
 mm/memory.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index e8ce066be5f2..eb027da68aa7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5405,6 +5405,8 @@ long copy_huge_page_from_user(struct page *dst_page,
 		if (rc)
 			break;
 
+		flush_dcache_page(subpage);
+
 		cond_resched();
 	}
 	return ret_val;
-- 
2.11.0