s390/kexec_file: fix diag308 subcode when loading crash kernel

commit 613775d upstream.

diag308 subcode 0 performes a clear reset which inlcudes the reset of
all registers in the system. While this is the preferred behavior when
loading a normal kernel via kexec it prevents the crash kernel to store
the register values in the dump. To prevent this use subcode 1 when
loading a crash kernel instead.

Fixes: ee337f5 ("s390/kexec_file: Add crash support to image loader")
Cc: <stable@vger.kernel.org> # 4.17
Signed-off-by: Philipp Rudo <prudo@linux.ibm.com>
Reported-by: Xiaoying Yan <yiyan@redhat.com>
Tested-by: Lianbo Jiang <lijiang@redhat.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/s390/purgatory/head.S

@@ -62,14 +62,15 @@
 	jh	10b
 .endm
 
-.macro START_NEXT_KERNEL base
+.macro START_NEXT_KERNEL base subcode
 	lg	%r4,kernel_entry-\base(%r13)
 	lg	%r5,load_psw_mask-\base(%r13)
 	ogr	%r4,%r5
 	stg	%r4,0(%r0)
 
 	xgr	%r0,%r0
-	diag	%r0,%r0,0x308
+	lghi	%r1,\subcode
+	diag	%r0,%r1,0x308
 .endm
 
 .text
@@ -123,7 +124,7 @@ ENTRY(purgatory_start)
 	je	.start_crash_kernel
 
 	/* start normal kernel */
-	START_NEXT_KERNEL .base_crash
+	START_NEXT_KERNEL .base_crash 0
 
 .return_old_kernel:
 	lmg	%r6,%r15,gprregs-.base_crash(%r13)
@@ -227,7 +228,7 @@ ENTRY(purgatory_start)
 	MEMCPY	%r9,%r10,%r11
 
 	/* start crash kernel */
-	START_NEXT_KERNEL .base_dst
+	START_NEXT_KERNEL .base_dst 1
 
 
 load_psw_mask: