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

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org>.

thanks,

greg k-h

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

From 19b482c29b6f3805f1d8e93015847b89e2f7f3b1 Mon Sep 17 00:00:00 2001
From: Muchun Song <songmuchun@bytedance.com>
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.

Link: https://lkml.kernel.org/r/20220210123058.79206-6-songmuchun@bytedance.com
Fixes: 8d1039634206 ("userfaultfd: shmem: add shmem_mfill_zeropage_pte for userfaultfd support")
Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Fam Zheng <fam.zheng@bytedance.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lars Persson <lars.persson@axis.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/shmem.c b/mm/shmem.c
index f21eb0ef8ae0..01fd227b6947 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -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;