s390: remove unused s390_base_ext_handler

s390_base_ext_handler_fn haven't been used since its introduction in
commit ab14de6c ("[S390] Convert memory detection into C code.").

s390_base_ext_handler itself is currently falsely storing 16 registers
at __LC_SAVE_AREA_ASYNC rewriting several following lowcore values:
cpu_flags, return_psw, return_mcck_psw, sync_enter_timer and
async_enter_timer.

Besides that s390_base_ext_handler itself is only potentially hiding
EXT interrupts which should not have happen in the first place. Any
piece of code which requires EXT interrupts before fully functional
ext_int_handler is enabled has to do it on its own, like this is done
by sclp_early_cmd() which is doing EXT interrupts handling synchronously
in sclp_early_wait_irq().

With s390_base_ext_handler removed unexpected EXT interrupt leads
to disabled wait with the address 0x1b0 (__LC_EXT_NEW_PSW), which is
currently setup in the decompressor.
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/include/asm/processor.h

@@ -318,14 +318,10 @@ static __always_inline void __noreturn disabled_wait(void)
 }
 
 /*
- * Basic Machine Check/Program Check Handler.
+ * Basic Program Check Handler.
  */
-
 extern void s390_base_pgm_handler(void);
-extern void s390_base_ext_handler(void);
-
 extern void (*s390_base_pgm_handler_fn)(void);
-extern void (*s390_base_ext_handler_fn)(void);
 
 #define ARCH_LOW_ADDRESS_LIMIT	0x7fffffffUL
 

arch/s390/kernel/base.S

@@ -11,32 +11,10 @@
 #include <asm/asm-offsets.h>
 #include <asm/nospec-insn.h>
 #include <asm/ptrace.h>
-#include <asm/sigp.h>
 
 	GEN_BR_THUNK %r9
 	GEN_BR_THUNK %r14
 
-ENTRY(s390_base_ext_handler)
-	stmg	%r0,%r15,__LC_SAVE_AREA_ASYNC
-	basr	%r13,0
-0:	aghi	%r15,-STACK_FRAME_OVERHEAD
-	larl	%r1,s390_base_ext_handler_fn
-	lg	%r9,0(%r1)
-	ltgr	%r9,%r9
-	jz	1f
-	BASR_EX	%r14,%r9
-1:	lmg	%r0,%r15,__LC_SAVE_AREA_ASYNC
-	ni	__LC_EXT_OLD_PSW+1,0xfd	# clear wait state bit
-	lpswe	__LC_EXT_OLD_PSW
-ENDPROC(s390_base_ext_handler)
-
-	.section .bss
-	.align 8
-	.globl s390_base_ext_handler_fn
-s390_base_ext_handler_fn:
-	.quad	0
-	.previous
-
 ENTRY(s390_base_pgm_handler)
 	stmg	%r0,%r15,__LC_SAVE_AREA_SYNC
 	basr	%r13,0

arch/s390/kernel/early.c

@@ -169,12 +169,10 @@ static noinline __init void setup_lowcore_early(void)
 {
 	psw_t psw;
 
+	psw.addr = (unsigned long)s390_base_pgm_handler;
 	psw.mask = PSW_MASK_BASE | PSW_DEFAULT_KEY | PSW_MASK_EA | PSW_MASK_BA;
 	if (IS_ENABLED(CONFIG_KASAN))
 		psw.mask |= PSW_MASK_DAT;
-	psw.addr = (unsigned long) s390_base_ext_handler;
-	S390_lowcore.external_new_psw = psw;
-	psw.addr = (unsigned long) s390_base_pgm_handler;
 	S390_lowcore.program_new_psw = psw;
 	s390_base_pgm_handler_fn = early_pgm_check_handler;
 	S390_lowcore.preempt_count = INIT_PREEMPT_COUNT;