s390: add support for virtually mapped kernel stacks

With virtually mapped kernel stacks the kernel stack overflow detection
is now fault based, every stack has a guard page in the vmalloc space.
The panic_stack is renamed to nodat_stack and is used for all function
that need to run without DAT, e.g. memcpy_real or do_start_kdump.

The main effect is a reduction in the kernel image size as with vmap
stacks the old style overflow checking that adds two instructions per
function is not needed anymore. Result from bloat-o-meter:

add/remove: 20/1 grow/shrink: 13/26854 up/down: 2198/-216240 (-214042)

In regard to performance the micro-benchmark for fork has a hit of a
few microseconds, allocating 4 pages in vmalloc space is more expensive
compare to an order-2 page allocation. But with real workload I could
not find a noticeable difference.
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Kconfig

@@ -125,6 +125,7 @@ config S390
 	select HAVE_ARCH_SOFT_DIRTY
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
+	select HAVE_ARCH_VMAP_STACK
 	select HAVE_EBPF_JIT if PACK_STACK && HAVE_MARCH_Z196_FEATURES
 	select HAVE_CMPXCHG_DOUBLE
 	select HAVE_CMPXCHG_LOCAL
@@ -649,6 +650,7 @@ config PACK_STACK
 
 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

arch/s390/include/asm/lowcore.h

@@ -102,9 +102,9 @@ struct lowcore {
 	__u64	current_task;			/* 0x0338 */
 	__u64	kernel_stack;			/* 0x0340 */
 
-	/* Interrupt, panic and restart stack. */
+	/* Interrupt, DAT-off and restartstack. */
 	__u64	async_stack;			/* 0x0348 */
-	__u64	panic_stack;			/* 0x0350 */
+	__u64	nodat_stack;			/* 0x0350 */
 	__u64	restart_stack;			/* 0x0358 */
 
 	/* Restart function and parameter. */

arch/s390/include/asm/processor.h

@@ -162,6 +162,14 @@ struct thread_struct {
 
 typedef struct thread_struct thread_struct;
 
+/*
+ * General size of a stack
+ */
+#define STACK_ORDER 2
+#define STACK_SIZE (PAGE_SIZE << STACK_ORDER)
+#define STACK_INIT_OFFSET \
+	(STACK_SIZE - STACK_FRAME_OVERHEAD - sizeof(struct pt_regs))
+
 /*
  * Stack layout of a C stack frame.
  */

arch/s390/include/asm/thread_info.h

@@ -14,10 +14,7 @@
  * Size of kernel stack for each process
  */
 #define THREAD_SIZE_ORDER 2
-#define ASYNC_ORDER  2
-
 #define THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER)
-#define ASYNC_SIZE  (PAGE_SIZE << ASYNC_ORDER)
 
 #ifndef __ASSEMBLY__
 #include <asm/lowcore.h>

arch/s390/kernel/asm-offsets.c

@@ -159,7 +159,7 @@ int main(void)
 	OFFSET(__LC_CURRENT, lowcore, current_task);
 	OFFSET(__LC_KERNEL_STACK, lowcore, kernel_stack);
 	OFFSET(__LC_ASYNC_STACK, lowcore, async_stack);
-	OFFSET(__LC_PANIC_STACK, lowcore, panic_stack);
+	OFFSET(__LC_NODAT_STACK, lowcore, nodat_stack);
 	OFFSET(__LC_RESTART_STACK, lowcore, restart_stack);
 	OFFSET(__LC_RESTART_FN, lowcore, restart_fn);
 	OFFSET(__LC_RESTART_DATA, lowcore, restart_data);

arch/s390/kernel/base.S

@@ -18,7 +18,7 @@
 
 ENTRY(s390_base_mcck_handler)
 	basr	%r13,0
-0:	lg	%r15,__LC_PANIC_STACK	# load panic stack
+0:	lg	%r15,__LC_NODAT_STACK	# load panic stack
 	aghi	%r15,-STACK_FRAME_OVERHEAD
 	larl	%r1,s390_base_mcck_handler_fn
 	lg	%r9,0(%r1)

arch/s390/kernel/dumpstack.c

@@ -77,11 +77,11 @@ void dump_trace(dump_trace_func_t func, void *data, struct task_struct *task,
 	frame_size = STACK_FRAME_OVERHEAD + sizeof(struct pt_regs);
 #ifdef CONFIG_CHECK_STACK
 	sp = __dump_trace(func, data, sp,
-			  S390_lowcore.panic_stack + frame_size - PAGE_SIZE,
-			  S390_lowcore.panic_stack + frame_size);
+			  S390_lowcore.nodat_stack + frame_size - STACK_SIZE,
+			  S390_lowcore.nodat_stack + frame_size);
 #endif
 	sp = __dump_trace(func, data, sp,
-			  S390_lowcore.async_stack + frame_size - ASYNC_SIZE,
+			  S390_lowcore.async_stack + frame_size - STACK_SIZE,
 			  S390_lowcore.async_stack + frame_size);
 	task = task ?: current;
 	__dump_trace(func, data, sp,

arch/s390/kernel/entry.S

@@ -85,14 +85,34 @@ _LPP_OFFSET	= __LC_LPP
 #endif
 	.endm
 
-	.macro	CHECK_STACK stacksize,savearea
+	.macro	CHECK_STACK savearea
 #ifdef CONFIG_CHECK_STACK
-	tml	%r15,\stacksize - CONFIG_STACK_GUARD
+	tml	%r15,STACK_SIZE - CONFIG_STACK_GUARD
 	lghi	%r14,\savearea
 	jz	stack_overflow
 #endif
 	.endm
 
+	.macro	CHECK_VMAP_STACK savearea,oklabel
+#ifdef CONFIG_VMAP_STACK
+	lgr	%r14,%r15
+	nill	%r14,0x10000 - STACK_SIZE
+	oill	%r14,STACK_INIT
+	clg	%r14,__LC_KERNEL_STACK
+	je	\oklabel
+	clg	%r14,__LC_ASYNC_STACK
+	je	\oklabel
+	clg	%r14,__LC_NODAT_STACK
+	je	\oklabel
+	clg	%r14,__LC_RESTART_STACK
+	je	\oklabel
+	lghi	%r14,\savearea
+	j	stack_overflow
+#else
+	j	\oklabel
+#endif
+	.endm
+
 	.macro	SWITCH_ASYNC savearea,timer
 	tmhh	%r8,0x0001		# interrupting from user ?
 	jnz	1f
@@ -104,11 +124,11 @@ _LPP_OFFSET	= __LC_LPP
 	brasl	%r14,cleanup_critical
 	tmhh	%r8,0x0001		# retest problem state after cleanup
 	jnz	1f
-0:	lg	%r14,__LC_ASYNC_STACK	# are we already on the async stack?
+0:	lg	%r14,__LC_ASYNC_STACK	# are we already on the target stack?
 	slgr	%r14,%r15
 	srag	%r14,%r14,STACK_SHIFT
 	jnz	2f
-	CHECK_STACK 1<<STACK_SHIFT,\savearea
+	CHECK_STACK \savearea
 	aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
 	j	3f
 1:	UPDATE_VTIME %r14,%r15,\timer
@@ -600,9 +620,10 @@ ENTRY(pgm_check_handler)
 	jnz	1f			# -> enabled, can't be a double fault
 	tm	__LC_PGM_ILC+3,0x80	# check for per exception
 	jnz	.Lpgm_svcper		# -> single stepped svc
-1:	CHECK_STACK STACK_SIZE,__LC_SAVE_AREA_SYNC
+1:	CHECK_STACK __LC_SAVE_AREA_SYNC
 	aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
-	j	4f
+	# CHECK_VMAP_STACK branches to stack_overflow or 4f
+	CHECK_VMAP_STACK __LC_SAVE_AREA_SYNC,4f
 2:	UPDATE_VTIME %r14,%r15,__LC_SYNC_ENTER_TIMER
 	BPENTER __TI_flags(%r12),_TIF_ISOLATE_BP
 	lg	%r15,__LC_KERNEL_STACK
@@ -1136,7 +1157,8 @@ ENTRY(mcck_int_handler)
 	jnz	4f
 	TSTMSK	__LC_MCCK_CODE,MCCK_CODE_PSW_IA_VALID
 	jno	.Lmcck_panic
-4:	SWITCH_ASYNC __LC_GPREGS_SAVE_AREA+64,__LC_MCCK_ENTER_TIMER
+4:	ssm	__LC_PGM_NEW_PSW	# turn dat on, keep irqs off
+	SWITCH_ASYNC __LC_GPREGS_SAVE_AREA+64,__LC_MCCK_ENTER_TIMER
 .Lmcck_skip:
 	lghi	%r14,__LC_GPREGS_SAVE_AREA+64
 	stmg	%r0,%r7,__PT_R0(%r11)
@@ -1163,7 +1185,6 @@ ENTRY(mcck_int_handler)
 	xc	__SF_BACKCHAIN(8,%r1),__SF_BACKCHAIN(%r1)
 	la	%r11,STACK_FRAME_OVERHEAD(%r1)
 	lgr	%r15,%r1
-	ssm	__LC_PGM_NEW_PSW	# turn dat on, keep irqs off
 	TSTMSK	__LC_CPU_FLAGS,_CIF_MCCK_PENDING
 	jno	.Lmcck_return
 	TRACE_IRQS_OFF
@@ -1182,7 +1203,7 @@ ENTRY(mcck_int_handler)
 	lpswe	__LC_RETURN_MCCK_PSW
 
 .Lmcck_panic:
-	lg	%r15,__LC_PANIC_STACK
+	lg	%r15,__LC_NODAT_STACK
 	la	%r11,STACK_FRAME_OVERHEAD(%r15)
 	j	.Lmcck_skip
 
@@ -1193,12 +1214,10 @@ ENTRY(restart_int_handler)
 	ALTERNATIVE "", ".insn s,0xb2800000,_LPP_OFFSET", 40
 	stg	%r15,__LC_SAVE_AREA_RESTART
 	lg	%r15,__LC_RESTART_STACK
-	aghi	%r15,-__PT_SIZE			# create pt_regs on stack
-	xc	0(__PT_SIZE,%r15),0(%r15)
-	stmg	%r0,%r14,__PT_R0(%r15)
-	mvc	__PT_R15(8,%r15),__LC_SAVE_AREA_RESTART
-	mvc	__PT_PSW(16,%r15),__LC_RST_OLD_PSW # store restart old psw
-	aghi	%r15,-STACK_FRAME_OVERHEAD	# create stack frame on stack
+	xc	STACK_FRAME_OVERHEAD(__PT_SIZE,%r15),STACK_FRAME_OVERHEAD(%r15)
+	stmg	%r0,%r14,STACK_FRAME_OVERHEAD+__PT_R0(%r15)
+	mvc	STACK_FRAME_OVERHEAD+__PT_R15(8,%r15),__LC_SAVE_AREA_RESTART
+	mvc	STACK_FRAME_OVERHEAD+__PT_PSW(16,%r15),__LC_RST_OLD_PSW
 	xc	0(STACK_FRAME_OVERHEAD,%r15),0(%r15)
 	lg	%r1,__LC_RESTART_FN		# load fn, parm & source cpu
 	lg	%r2,__LC_RESTART_DATA
@@ -1216,14 +1235,14 @@ ENTRY(restart_int_handler)
 
 	.section .kprobes.text, "ax"
 
-#ifdef CONFIG_CHECK_STACK
+#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.
  * Setup a pt_regs so that show_trace can provide a good call trace.
  */
 stack_overflow:
-	lg	%r15,__LC_PANIC_STACK	# change to panic stack
+	lg	%r15,__LC_NODAT_STACK	# change to panic stack
 	la	%r11,STACK_FRAME_OVERHEAD(%r15)
 	stmg	%r0,%r7,__PT_R0(%r11)
 	stmg	%r8,%r9,__PT_PSW(%r11)

arch/s390/kernel/entry.h

@@ -86,4 +86,7 @@ DECLARE_PER_CPU(u64, mt_cycles[8]);
 void gs_load_bc_cb(struct pt_regs *regs);
 void set_fs_fixup(void);
 
+unsigned long stack_alloc(void);
+void stack_free(unsigned long stack);
+
 #endif /* _ENTRY_H */

arch/s390/kernel/head64.S

@@ -36,9 +36,7 @@ ENTRY(startup_continue)
 #
 	larl	%r14,init_task
 	stg	%r14,__LC_CURRENT
-	larl	%r15,init_thread_union+THREAD_SIZE
-	stg	%r15,__LC_KERNEL_STACK	# set end of kernel stack
-	aghi	%r15,-STACK_FRAME_OVERHEAD
+	larl	%r15,init_thread_union+THREAD_SIZE-STACK_FRAME_OVERHEAD
 #
 # Early setup functions that may not rely on an initialized bss section,
 # like moving the initrd. Returns with an initialized bss section.

arch/s390/kernel/irq.c

@@ -171,7 +171,7 @@ void do_softirq_own_stack(void)
 	old = current_stack_pointer();
 	/* Check against async. stack address range. */
 	new = S390_lowcore.async_stack;
-	if (((new - old) >> (PAGE_SHIFT + THREAD_SIZE_ORDER)) != 0) {
+	if (((new - old) >> (PAGE_SHIFT + STACK_ORDER)) != 0) {
 		CALL_ON_STACK(__do_softirq, new, 0);
 	} else {
 		/* We are already on the async stack. */

arch/s390/kernel/machine_kexec.c

@@ -142,18 +142,27 @@ static noinline void __machine_kdump(void *image)
 }
 #endif
 
+static unsigned long do_start_kdump(unsigned long addr)
+{
+	struct kimage *image = (struct kimage *) addr;
+	int (*start_kdump)(int) = (void *)image->start;
+	int rc;
+
+	__arch_local_irq_stnsm(0xfb); /* disable DAT */
+	rc = start_kdump(0);
+	__arch_local_irq_stosm(0x04); /* enable DAT */
+	return rc;
+}
+
 /*
  * Check if kdump checksums are valid: We call purgatory with parameter "0"
  */
 static bool kdump_csum_valid(struct kimage *image)
 {
 #ifdef CONFIG_CRASH_DUMP
-	int (*start_kdump)(int) = (void *)image->start;
 	int rc;
 
-	__arch_local_irq_stnsm(0xfb); /* disable DAT */
-	rc = start_kdump(0);
-	__arch_local_irq_stosm(0x04); /* enable DAT */
+	rc = CALL_ON_STACK(do_start_kdump, S390_lowcore.nodat_stack, 1, image);
 	return rc == 0;
 #else
 	return false;

arch/s390/kernel/setup.c

@@ -49,6 +49,7 @@
 #include <linux/crash_dump.h>
 #include <linux/memory.h>
 #include <linux/compat.h>
+#include <linux/start_kernel.h>
 
 #include <asm/ipl.h>
 #include <asm/facility.h>
@@ -303,6 +304,78 @@ early_param("vmalloc", parse_vmalloc);
 
 void *restart_stack __section(.data);
 
+unsigned long stack_alloc(void)
+{
+#ifdef CONFIG_VMAP_STACK
+	return (unsigned long)
+		__vmalloc_node_range(STACK_SIZE, STACK_SIZE,
+				     VMALLOC_START, VMALLOC_END,
+				     THREADINFO_GFP,
+				     PAGE_KERNEL, 0, NUMA_NO_NODE,
+				     __builtin_return_address(0));
+#else
+	return __get_free_pages(GFP_KERNEL, STACK_ORDER);
+#endif
+}
+
+void stack_free(unsigned long stack)
+{
+#ifdef CONFIG_VMAP_STACK
+	vfree((void *) stack);
+#else
+	free_pages(stack, STACK_ORDER);
+#endif
+}
+
+int __init arch_early_irq_init(void)
+{
+	unsigned long stack;
+
+	stack = __get_free_pages(GFP_KERNEL, STACK_ORDER);
+	if (!stack)
+		panic("Couldn't allocate async stack");
+	S390_lowcore.async_stack = stack + STACK_INIT_OFFSET;
+	return 0;
+}
+
+static int __init async_stack_realloc(void)
+{
+	unsigned long old, new;
+
+	old = S390_lowcore.async_stack - STACK_INIT_OFFSET;
+	new = stack_alloc();
+	if (!new)
+		panic("Couldn't allocate async stack");
+	S390_lowcore.async_stack = new + STACK_INIT_OFFSET;
+	free_pages(old, STACK_ORDER);
+	return 0;
+}
+early_initcall(async_stack_realloc);
+
+void __init arch_call_rest_init(void)
+{
+	struct stack_frame *frame;
+	unsigned long stack;
+
+	stack = stack_alloc();
+	if (!stack)
+		panic("Couldn't allocate kernel stack");
+	current->stack = (void *) stack;
+#ifdef CONFIG_VMAP_STACK
+	current->stack_vm_area = (void *) stack;
+#endif
+	set_task_stack_end_magic(current);
+	stack += STACK_INIT_OFFSET;
+	S390_lowcore.kernel_stack = stack;
+	frame = (struct stack_frame *) stack;
+	memset(frame, 0, sizeof(*frame));
+	/* Branch to rest_init on the new stack, never returns */
+	asm volatile(
+		"	la	15,0(%[_frame])\n"
+		"	jg	rest_init\n"
+		: : [_frame] "a" (frame));
+}
+
 static void __init setup_lowcore(void)
 {
 	struct lowcore *lc;
@@ -329,14 +402,8 @@ static void __init setup_lowcore(void)
 		PSW_MASK_DAT | PSW_MASK_MCHECK;
 	lc->io_new_psw.addr = (unsigned long) io_int_handler;
 	lc->clock_comparator = clock_comparator_max;
-	lc->kernel_stack = ((unsigned long) &init_thread_union)
+	lc->nodat_stack = ((unsigned long) &init_thread_union)
 		+ THREAD_SIZE - STACK_FRAME_OVERHEAD - sizeof(struct pt_regs);
-	lc->async_stack = (unsigned long)
-		memblock_virt_alloc(ASYNC_SIZE, ASYNC_SIZE)
-		+ ASYNC_SIZE - STACK_FRAME_OVERHEAD - sizeof(struct pt_regs);
-	lc->panic_stack = (unsigned long)
-		memblock_virt_alloc(PAGE_SIZE, PAGE_SIZE)
-		+ PAGE_SIZE - STACK_FRAME_OVERHEAD - sizeof(struct pt_regs);
 	lc->current_task = (unsigned long)&init_task;
 	lc->lpp = LPP_MAGIC;
 	lc->machine_flags = S390_lowcore.machine_flags;
@@ -357,8 +424,12 @@ static void __init setup_lowcore(void)
 	lc->last_update_timer = S390_lowcore.last_update_timer;
 	lc->last_update_clock = S390_lowcore.last_update_clock;
 
-	restart_stack = memblock_virt_alloc(ASYNC_SIZE, ASYNC_SIZE);
-	restart_stack += ASYNC_SIZE;
+	/*
+	 * Allocate the global restart stack which is the same for
+	 * all CPUs in cast *one* of them does a PSW restart.
+	 */
+	restart_stack = memblock_virt_alloc(STACK_SIZE, STACK_SIZE);
+	restart_stack += STACK_INIT_OFFSET;
 
 	/*
 	 * Set up PSW restart to call ipl.c:do_restart(). Copy the relevant

arch/s390/kernel/smp.c

@@ -186,36 +186,34 @@ static void pcpu_ec_call(struct pcpu *pcpu, int ec_bit)
 	pcpu_sigp_retry(pcpu, order, 0);
 }
 
-#define ASYNC_FRAME_OFFSET (ASYNC_SIZE - STACK_FRAME_OVERHEAD - __PT_SIZE)
-#define PANIC_FRAME_OFFSET (PAGE_SIZE - STACK_FRAME_OVERHEAD - __PT_SIZE)
-
 static int pcpu_alloc_lowcore(struct pcpu *pcpu, int cpu)
 {
-	unsigned long async_stack, panic_stack;
+	unsigned long async_stack, nodat_stack;
 	struct lowcore *lc;
 
 	if (pcpu != &pcpu_devices[0]) {
 		pcpu->lowcore =	(struct lowcore *)
 			__get_free_pages(GFP_KERNEL | GFP_DMA, LC_ORDER);
-		async_stack = __get_free_pages(GFP_KERNEL, ASYNC_ORDER);
-		panic_stack = __get_free_page(GFP_KERNEL);
-		if (!pcpu->lowcore || !panic_stack || !async_stack)
+		nodat_stack = __get_free_pages(GFP_KERNEL, STACK_ORDER);
+		if (!pcpu->lowcore || !nodat_stack)
 			goto out;
 	} else {
-		async_stack = pcpu->lowcore->async_stack - ASYNC_FRAME_OFFSET;
-		panic_stack = pcpu->lowcore->panic_stack - PANIC_FRAME_OFFSET;
+		nodat_stack = pcpu->lowcore->nodat_stack - STACK_INIT_OFFSET;
 	}
+	async_stack = stack_alloc();
+	if (!async_stack)
+		goto out;
 	lc = pcpu->lowcore;
 	memcpy(lc, &S390_lowcore, 512);
 	memset((char *) lc + 512, 0, sizeof(*lc) - 512);
-	lc->async_stack = async_stack + ASYNC_FRAME_OFFSET;
-	lc->panic_stack = panic_stack + PANIC_FRAME_OFFSET;
+	lc->async_stack = async_stack + STACK_INIT_OFFSET;
+	lc->nodat_stack = nodat_stack + STACK_INIT_OFFSET;
 	lc->cpu_nr = cpu;
 	lc->spinlock_lockval = arch_spin_lockval(cpu);
 	lc->spinlock_index = 0;
 	lc->br_r1_trampoline = 0x07f1;	/* br %r1 */
 	if (nmi_alloc_per_cpu(lc))
-		goto out;
+		goto out_async;
 	if (vdso_alloc_per_cpu(lc))
 		goto out_mcesa;
 	lowcore_ptr[cpu] = lc;
@@ -224,10 +222,11 @@ static int pcpu_alloc_lowcore(struct pcpu *pcpu, int cpu)
 
 out_mcesa:
 	nmi_free_per_cpu(lc);
+out_async:
+	stack_free(async_stack);
 out:
 	if (pcpu != &pcpu_devices[0]) {
-		free_page(panic_stack);
-		free_pages(async_stack, ASYNC_ORDER);
+		free_pages(nodat_stack, STACK_ORDER);
 		free_pages((unsigned long) pcpu->lowcore, LC_ORDER);
 	}
 	return -ENOMEM;
@@ -237,15 +236,21 @@ static int pcpu_alloc_lowcore(struct pcpu *pcpu, int cpu)
 
 static void pcpu_free_lowcore(struct pcpu *pcpu)
 {
+	unsigned long async_stack, nodat_stack, lowcore;
+
+	nodat_stack = pcpu->lowcore->nodat_stack - STACK_INIT_OFFSET;
+	async_stack = pcpu->lowcore->async_stack - STACK_INIT_OFFSET;
+	lowcore = (unsigned long) pcpu->lowcore;
+
 	pcpu_sigp_retry(pcpu, SIGP_SET_PREFIX, 0);
 	lowcore_ptr[pcpu - pcpu_devices] = NULL;
 	vdso_free_per_cpu(pcpu->lowcore);
 	nmi_free_per_cpu(pcpu->lowcore);
+	stack_free(async_stack);
 	if (pcpu == &pcpu_devices[0])
 		return;
-	free_page(pcpu->lowcore->panic_stack-PANIC_FRAME_OFFSET);
-	free_pages(pcpu->lowcore->async_stack-ASYNC_FRAME_OFFSET, ASYNC_ORDER);
-	free_pages((unsigned long) pcpu->lowcore, LC_ORDER);
+	free_pages(nodat_stack, STACK_ORDER);
+	free_pages(lowcore, LC_ORDER);
 }
 
 #endif /* CONFIG_HOTPLUG_CPU */
@@ -293,7 +298,7 @@ static void pcpu_start_fn(struct pcpu *pcpu, void (*func)(void *), void *data)
 {
 	struct lowcore *lc = pcpu->lowcore;
 
-	lc->restart_stack = lc->kernel_stack;
+	lc->restart_stack = lc->nodat_stack;
 	lc->restart_fn = (unsigned long) func;
 	lc->restart_data = (unsigned long) data;
 	lc->restart_source = -1UL;
@@ -303,15 +308,20 @@ static void pcpu_start_fn(struct pcpu *pcpu, void (*func)(void *), void *data)
 /*
  * Call function via PSW restart on pcpu and stop the current cpu.
  */
+static void __pcpu_delegate(void (*func)(void*), void *data)
+{
+	func(data);	/* should not return */
+}
+
 static void pcpu_delegate(struct pcpu *pcpu, void (*func)(void *),
 			  void *data, unsigned long stack)
 {
 	struct lowcore *lc = lowcore_ptr[pcpu - pcpu_devices];
 	unsigned long source_cpu = stap();
 
-	__load_psw_mask(PSW_KERNEL_BITS);
+	__load_psw_mask(PSW_KERNEL_BITS | PSW_MASK_DAT);
 	if (pcpu->address == source_cpu)
-		func(data);	/* should not return */
+		CALL_ON_STACK(__pcpu_delegate, stack, 2, func, data);
 	/* Stop target cpu (if func returns this stops the current cpu). */
 	pcpu_sigp_retry(pcpu, SIGP_STOP, 0);
 	/* Restart func on the target cpu and stop the current cpu. */
@@ -372,8 +382,7 @@ void smp_call_online_cpu(void (*func)(void *), void *data)
 void smp_call_ipl_cpu(void (*func)(void *), void *data)
 {
 	pcpu_delegate(&pcpu_devices[0], func, data,
-		      pcpu_devices->lowcore->panic_stack -
-		      PANIC_FRAME_OFFSET + PAGE_SIZE);
+		      pcpu_devices->lowcore->nodat_stack);
 }
 
 int smp_find_processor_id(u16 address)
@@ -791,37 +800,42 @@ void __init smp_detect_cpus(void)
 	memblock_free_early((unsigned long)info, sizeof(*info));
 }
 
-/*
- *	Activate a secondary processor.
- */
-static void smp_start_secondary(void *cpuvoid)
+static void smp_init_secondary(void)
 {
 	int cpu = smp_processor_id();
 
-	S390_lowcore.last_update_clock = get_tod_clock();
-	S390_lowcore.restart_stack = (unsigned long) restart_stack;
-	S390_lowcore.restart_fn = (unsigned long) do_restart;
-	S390_lowcore.restart_data = 0;
-	S390_lowcore.restart_source = -1UL;
-	restore_access_regs(S390_lowcore.access_regs_save_area);
-	__ctl_load(S390_lowcore.cregs_save_area, 0, 15);
-	__load_psw_mask(PSW_KERNEL_BITS | PSW_MASK_DAT);
 	cpu_init();
 	preempt_disable();
 	init_cpu_timer();
 	vtime_init();
 	pfault_init();
-	notify_cpu_starting(cpu);
+	notify_cpu_starting(smp_processor_id());
 	if (topology_cpu_dedicated(cpu))
 		set_cpu_flag(CIF_DEDICATED_CPU);
 	else
 		clear_cpu_flag(CIF_DEDICATED_CPU);
-	set_cpu_online(cpu, true);
+	set_cpu_online(smp_processor_id(), true);
 	inc_irq_stat(CPU_RST);
 	local_irq_enable();
 	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
 }
 
+/*
+ *	Activate a secondary processor.
+ */
+static void smp_start_secondary(void *cpuvoid)
+{
+	S390_lowcore.last_update_clock = get_tod_clock();
+	S390_lowcore.restart_stack = (unsigned long) restart_stack;
+	S390_lowcore.restart_fn = (unsigned long) do_restart;
+	S390_lowcore.restart_data = 0;
+	S390_lowcore.restart_source = -1UL;
+	restore_access_regs(S390_lowcore.access_regs_save_area);
+	__ctl_load(S390_lowcore.cregs_save_area, 0, 15);
+	__load_psw_mask(PSW_KERNEL_BITS | PSW_MASK_DAT);
+	CALL_ON_STACK(smp_init_secondary, S390_lowcore.kernel_stack, 0);
+}
+
 /* Upping and downing of CPUs */
 int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 {

arch/s390/kernel/swsusp.S

@@ -29,10 +29,11 @@
 
 	.section .text
 ENTRY(swsusp_arch_suspend)
-	stmg	%r6,%r15,__SF_GPRS(%r15)
+	lg	%r1,__LC_NODAT_STACK
+	aghi	%r1,-STACK_FRAME_OVERHEAD
+	stmg	%r6,%r15,__SF_GPRS(%r1)
+	stg	%r15,__SF_BACKCHAIN(%r1)
 	lgr	%r1,%r15
-	aghi	%r15,-STACK_FRAME_OVERHEAD
-	stg	%r1,__SF_BACKCHAIN(%r15)
 
 	/* Store FPU registers */
 	brasl	%r14,save_fpu_regs

arch/s390/mm/maccess.c

@@ -89,10 +89,8 @@ static int __memcpy_real(void *dest, void *src, size_t count)
 	return rc;
 }
 
-/*
- * Copy memory in real mode (kernel to kernel)
- */
-int memcpy_real(void *dest, void *src, size_t count)
+static unsigned long _memcpy_real(unsigned long dest, unsigned long src,
+				  unsigned long count)
 {
 	int irqs_disabled, rc;
 	unsigned long flags;
@@ -103,13 +101,30 @@ int memcpy_real(void *dest, void *src, size_t count)
 	irqs_disabled = arch_irqs_disabled_flags(flags);
 	if (!irqs_disabled)
 		trace_hardirqs_off();
-	rc = __memcpy_real(dest, src, count);
+	rc = __memcpy_real((void *) dest, (void *) src, (size_t) count);
 	if (!irqs_disabled)
 		trace_hardirqs_on();
 	__arch_local_irq_ssm(flags);
 	return rc;
 }
 
+/*
+ * Copy memory in real mode (kernel to kernel)
+ */
+int memcpy_real(void *dest, void *src, size_t count)
+{
+	if (S390_lowcore.nodat_stack != 0)
+		return CALL_ON_STACK(_memcpy_real, S390_lowcore.nodat_stack,
+				     3, dest, src, count);
+	/*
+	 * This is a really early memcpy_real call, the stacks are
+	 * not set up yet. Just call _memcpy_real on the early boot
+	 * stack
+	 */
+	return _memcpy_real((unsigned long) dest,(unsigned long) src,
+			    (unsigned long) count);
+}
+
 /*
  * Copy memory in absolute mode (kernel to kernel)
  */