From a6e49f10f4411ec87f16ccb1b0ce5ea7e4a04a95 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <hca@linux.ibm.com>
Date: Fri, 25 Aug 2023 14:29:50 +0200
Subject: [PATCH] s390/mm: improve description of mapping permissions of prefix
pages
Slightly improve the description which explains why the first prefix
page must be mapped executable when the BEAR-enhancement facility is
not installed.
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/mm/vmem.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index 9b31dc565bc5e..a1e01542790b2 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -659,8 +659,11 @@ void __init vmem_map_init(void)
(unsigned long)(_einittext - _sinittext) >> PAGE_SHIFT);
set_memory_rox((unsigned long)__stext_amode31,
(unsigned long)(__etext_amode31 - __stext_amode31) >> PAGE_SHIFT);
-
- /* lowcore must be executable for LPSWE */
+ /*
+ * If the BEAR-enhancement facility is not installed the first
+ * prefix page is used to return to the previous context with
+ * an LPSWE instruction and therefore must be executable.
+ */
if (!static_key_enabled(&cpu_has_bear))
set_memory_x(0, 1);
if (debug_pagealloc_enabled()) {
--
GitLab