s390/Kconfig: Select VMAP_STACK unconditionally

There is no point in supporting !VMAP_STACK kernel builds. VMAP_STACK has
proven to work since many years. Also, since KASAN_VMALLOC is supported,
kernels built with !VMAP_STACK are completely untested.

Therefore select VMAP_STACK unconditionally and remove all config options
and code required for !VMAP_STACK builds.

Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/Kconfig

@@ -256,6 +256,7 @@ config S390
 	select USER_STACKTRACE_SUPPORT
 	select VDSO_GETRANDOM
 	select VIRT_CPU_ACCOUNTING
+	select VMAP_STACK
 	select ZONE_DMA
 	# Note: keep the above list sorted alphabetically
 
@@ -689,32 +690,6 @@ config MAX_PHYSMEM_BITS
 	  Increasing the number of bits also increases the kernel image size.
 	  By default 46 bits (64TB) are supported.
 
-config CHECK_STACK
-	def_bool y
-	depends on !VMAP_STACK
-	prompt "Detect kernel stack overflow"
-	help
-	  This option enables the compiler option -mstack-guard and
-	  -mstack-size if they are available. If the compiler supports them
-	  it will emit additional code to each function prolog to trigger
-	  an illegal operation if the kernel stack is about to overflow.
-
-	  Say N if you are unsure.
-
-config STACK_GUARD
-	int "Size of the guard area (128-1024)"
-	range 128 1024
-	depends on CHECK_STACK
-	default "256"
-	help
-	  This allows you to specify the size of the guard area at the lower
-	  end of the kernel stack. If the kernel stack points into the guard
-	  area on function entry an illegal operation is triggered. The size
-	  needs to be a power of 2. Please keep in mind that the size of an
-	  interrupt frame is 184 bytes for 31 bit and 328 bytes on 64 bit.
-	  The minimum size for the stack guard should be 256 for 31 bit and
-	  512 for 64 bit.
-
 endmenu
 
 menu "I/O subsystem"

arch/s390/Makefile

@@ -72,15 +72,6 @@ cflags-$(CONFIG_FRAME_POINTER) += -fno-optimize-sibling-calls
 KBUILD_AFLAGS_DECOMPRESSOR += $(aflags-y)
 KBUILD_CFLAGS_DECOMPRESSOR += $(cflags-y)
 
-ifneq ($(call cc-option,-mstack-size=8192 -mstack-guard=128),)
-  CC_FLAGS_CHECK_STACK := -mstack-size=$(STACK_SIZE)
-  ifeq ($(call cc-option,-mstack-size=8192),)
-    CC_FLAGS_CHECK_STACK += -mstack-guard=$(CONFIG_STACK_GUARD)
-  endif
-  export CC_FLAGS_CHECK_STACK
-  cflags-$(CONFIG_CHECK_STACK) += $(CC_FLAGS_CHECK_STACK)
-endif
-
 ifdef CONFIG_EXPOLINE
   ifdef CONFIG_EXPOLINE_EXTERN
     CC_FLAGS_EXPOLINE := -mindirect-branch=thunk-extern

arch/s390/kernel/entry.S

@@ -52,16 +52,7 @@ _LPP_OFFSET	= __LC_LPP
 		ALT_FACILITY(193)
 	.endm
 
-	.macro	CHECK_STACK savearea, lowcore
-#ifdef CONFIG_CHECK_STACK
-	tml	%r15,THREAD_SIZE - CONFIG_STACK_GUARD
-	la	%r14,\savearea(\lowcore)
-	jz	stack_overflow
-#endif
-	.endm
-
 	.macro	CHECK_VMAP_STACK savearea, lowcore, oklabel
-#ifdef CONFIG_VMAP_STACK
 	lgr	%r14,%r15
 	nill	%r14,0x10000 - THREAD_SIZE
 	oill	%r14,STACK_INIT_OFFSET
@@ -77,9 +68,6 @@ _LPP_OFFSET	= __LC_LPP
 	je	\oklabel
 	la	%r14,\savearea(\lowcore)
 	j	stack_overflow
-#else
-	j	\oklabel
-#endif
 	.endm
 
 	/*
@@ -326,8 +314,7 @@ SYM_CODE_START(pgm_check_handler)
 	jnz	2f			# -> enabled, can't be a double fault
 	tm	__LC_PGM_ILC+3(%r13),0x80	# check for per exception
 	jnz	.Lpgm_svcper		# -> single stepped svc
-2:	CHECK_STACK __LC_SAVE_AREA,%r13
+2:	aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
-	aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
 	# CHECK_VMAP_STACK branches to stack_overflow or 4f
 	CHECK_VMAP_STACK __LC_SAVE_AREA,%r13,4f
 3:	lg	%r15,__LC_KERNEL_STACK(%r13)
@@ -394,8 +381,7 @@ SYM_CODE_START(\name)
 	BPENTER	__SF_SIE_FLAGS(%r15),_TIF_ISOLATE_BP_GUEST
 	SIEEXIT __SF_SIE_CONTROL(%r15),%r13
 #endif
-0:	CHECK_STACK __LC_SAVE_AREA,%r13
+0:	aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
-	aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
 	j	2f
 1:	lctlg	%c1,%c1,__LC_KERNEL_ASCE(%r13)
 	lg	%r15,__LC_KERNEL_STACK(%r13)
@@ -603,7 +589,6 @@ SYM_CODE_END(early_pgm_check_handler)
 
 	.section .kprobes.text, "ax"
 
-#if defined(CONFIG_CHECK_STACK) || defined(CONFIG_VMAP_STACK)
 /*
  * The synchronous or the asynchronous stack overflowed. We are dead.
  * No need to properly save the registers, we are going to panic anyway.
@@ -621,7 +606,6 @@ SYM_CODE_START(stack_overflow)
 	lgr	%r2,%r11		# pass pointer to pt_regs
 	jg	kernel_stack_overflow
 SYM_CODE_END(stack_overflow)
-#endif
 
 	.section .data, "aw"
 	.balign	4

arch/s390/kernel/setup.c

@@ -359,25 +359,17 @@ void *restart_stack;
 
 unsigned long stack_alloc(void)
 {
-#ifdef CONFIG_VMAP_STACK
 	void *ret;
 
 	ret = __vmalloc_node(THREAD_SIZE, THREAD_SIZE, THREADINFO_GFP,
 			     NUMA_NO_NODE, __builtin_return_address(0));
 	kmemleak_not_leak(ret);
 	return (unsigned long)ret;
-#else
-	return __get_free_pages(GFP_KERNEL, THREAD_SIZE_ORDER);
-#endif
 }
 
 void stack_free(unsigned long stack)
 {
-#ifdef CONFIG_VMAP_STACK
 	vfree((void *) stack);
-#else
-	free_pages(stack, THREAD_SIZE_ORDER);
-#endif
 }
 
 static unsigned long __init stack_alloc_early(void)

arch/s390/kernel/vdso64/Makefile

@@ -5,7 +5,7 @@
 include $(srctree)/lib/vdso/Makefile
 obj-vdso64 = vdso_user_wrapper.o note.o vgetrandom-chacha.o
 obj-cvdso64 = vdso64_generic.o getcpu.o vgetrandom.o
-VDSO_CFLAGS_REMOVE := -pg $(CC_FLAGS_FTRACE) $(CC_FLAGS_EXPOLINE) $(CC_FLAGS_CHECK_STACK)
+VDSO_CFLAGS_REMOVE := -pg $(CC_FLAGS_FTRACE) $(CC_FLAGS_EXPOLINE)
 CFLAGS_REMOVE_getcpu.o = $(VDSO_CFLAGS_REMOVE)
 CFLAGS_REMOVE_vgetrandom.o = $(VDSO_CFLAGS_REMOVE)
 CFLAGS_REMOVE_vdso64_generic.o = $(VDSO_CFLAGS_REMOVE)