FAILED: patch "[PATCH] mm: shmem: fix missing cache flush in" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 19b482c29b6f3805f1d8e93015847b89e2f7f3b1 Mon Sep 17 00:00:00 2001
From: Muchun Song <[email protected]>
Date: Tue, 22 Mar 2022 14:42:05 -0700
Subject: [PATCH] mm: shmem: fix missing cache flush in
shmem_mfill_atomic_pte()

userfaultfd calls shmem_mfill_atomic_pte() 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. Insert flush_dcache_page() in non-zero-page case. And replace clear_highpage() with clear_user_highpage() which already considers the cache maintenance.

index f21eb0ef8ae0..01fd227b6947 100644
@@ -2364,8 +2364,10 @@ int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
 				/* don't free the page */
 				goto out_unacct_blocks;
 			}
+
+			flush_dcache_page(page);
 		} else {		/* ZEROPAGE */
-			clear_highpage(page);
+			clear_user_highpage(page, dst_addr);
 		}
 	} else {
 		page = *pagep;