[PATCH RFC v8 18/56] x86/fault: fix handle_split_page_fault() to work with memfd backed pages

[Michael Roth]

From: Hugh Dickins <hughd@xxxxxxxxxx>

When the address is backed by a memfd, the code to split the page does
nothing more than remove the PMD from the page tables. So immediately
install a PTE to ensure that any other pages in that 2MB region are
brought back as in 4K pages.

Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
 mm/memory.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index e68da7e403c6..33c9020ba1f8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4999,6 +4999,11 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 static int handle_split_page_fault(struct vm_fault *vmf)
 {
 	__split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL);
+	/*
+	 * Install a PTE immediately to ensure that any other pages in
+	 * this 2MB region are brought back in as 4K pages.
+	 */
+	__pte_alloc(vmf->vma->vm_mm, vmf->pmd);
 	return 0;
 }
 
-- 
2.25.1