s390/kexec: fix crash on resize of reserved memory

Reducing the size of reserved memory for the crash kernel will result
in an immediate crash on s390. Reason for that is that we do not
create struct pages for memory that is reserved. If that memory is
freed any access to struct pages which correspond to this memory will
result in invalid memory accesses and a kernel panic.

Fix this by properly creating struct pages when the system gets
initialized. Change the code also to make use of set_memory_ro() and
set_memory_rw() so page tables will be split if required.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index d4e0742b197b..9b4bb9d9275f 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -432,6 +432,20 @@ static void __init setup_resources(void)
                         }
                 }
         }
+#ifdef CONFIG_CRASH_DUMP
+        /*
+         * Re-add removed crash kernel memory as reserved memory. This makes
+         * sure it will be mapped with the identity mapping and struct pages
+         * will be created, so it can be resized later on.
+         * However add it later since the crash kernel resource should not be
+         * part of the System RAM resource.
+         */
+        if (crashk_res.end) {
+                memblock_add(crashk_res.start, resource_size(&crashk_res));
+                memblock_reserve(crashk_res.start, resource_size(&crashk_res));
+                insert_resource(&iomem_resource, &crashk_res);
+        }
+#endif
 }
 
 static void __init setup_memory_end(void)
@@ -602,7 +616,6 @@ static void __init reserve_crashkernel(void)
                 diag10_range(PFN_DOWN(crash_base), PFN_DOWN(crash_size));
         crashk_res.start = crash_base;
         crashk_res.end = crash_base + crash_size - 1;
-        insert_resource(&iomem_resource, &crashk_res);
         memblock_remove(crash_base, crash_size);
         pr_info("Reserving %lluMB of memory at %lluMB "
                 "for crashkernel (System RAM: %luMB)\n",