s390/dump: rework CPU register dump code

To collect the CPU registers of the crashed system allocated a single
page with memblock_alloc_base and use it as a copy buffer. Replace the
stop-and-store-status sigp with a store-status-at-address sigp in
smp_save_dump_cpus() and smp_store_status(). In both cases the target
CPU is already stopped and store-status-at-address avoids the detour
via the absolute zero page.

For kexec simplify s390_reset_system and call store_status() before
the prefix register of the boot CPU has been set to zero. Use STPX
to store the prefix register and remove dump_prefix_page.

Acked-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/fpu/internal.h

@@ -12,21 +12,13 @@
 #include <asm/ctl_reg.h>
 #include <asm/fpu/types.h>
 
-static inline void save_vx_regs_safe(__vector128 *vxrs)
+static inline void save_vx_regs(__vector128 *vxrs)
 {
-	unsigned long cr0, flags;
-
-	flags = arch_local_irq_save();
-	__ctl_store(cr0, 0, 0);
-	__ctl_set_bit(0, 17);
-	__ctl_set_bit(0, 18);
 	asm volatile(
 		"	la	1,%0\n"
 		"	.word	0xe70f,0x1000,0x003e\n"	/* vstm 0,15,0(1) */
 		"	.word	0xe70f,0x1100,0x0c3e\n"	/* vstm 16,31,256(1) */
 		: "=Q" (*(struct vx_array *) vxrs) : : "1");
-	__ctl_load(cr0, 0, 0);
-	arch_local_irq_restore(flags);
 }
 
 static inline void convert_vx_to_fp(freg_t *fprs, __vector128 *vxrs)

arch/s390/include/asm/ipl.h

@@ -87,7 +87,6 @@ struct ipl_parameter_block {
  * IPL validity flags
  */
 extern u32 ipl_flags;
-extern u32 dump_prefix_page;
 
 struct dump_save_areas {
 	struct save_area_ext **areas;
@@ -176,7 +175,7 @@ enum diag308_rc {
 
 extern int diag308(unsigned long subcode, void *addr);
 extern void diag308_reset(void);
-extern void store_status(void);
+extern void store_status(void (*fn)(void *), void *data);
 extern void lgr_info_log(void);
 
 #endif /* _ASM_S390_IPL_H */

arch/s390/include/asm/reset.h

@@ -15,6 +15,5 @@ struct reset_call {
 
 extern void register_reset_call(struct reset_call *reset);
 extern void unregister_reset_call(struct reset_call *reset);
-extern void s390_reset_system(void (*fn_pre)(void),
-			      void (*fn_post)(void *), void *data);
+extern void s390_reset_system(void);
 #endif /* _ASM_S390_RESET_H */

arch/s390/include/asm/smp.h

@@ -18,6 +18,7 @@
 extern struct mutex smp_cpu_state_mutex;
 extern unsigned int smp_cpu_mt_shift;
 extern unsigned int smp_cpu_mtid;
+extern __vector128 __initdata boot_cpu_vector_save_area[__NUM_VXRS];
 
 extern int __cpu_up(unsigned int cpu, struct task_struct *tidle);
 
@@ -55,7 +56,6 @@ static inline int smp_store_status(int cpu) { return 0; }
 static inline int smp_vcpu_scheduled(int cpu) { return 1; }
 static inline void smp_yield_cpu(int cpu) { }
 static inline void smp_fill_possible_mask(void) { }
-static inline void smp_save_dump_cpus(void) { }
 
 #endif /* CONFIG_SMP */
 

arch/s390/kernel/early.c

@@ -335,6 +335,14 @@ static __init void detect_machine_facilities(void)
 	}
 }
 
+static inline void save_vector_registers(void)
+{
+#ifdef CONFIG_CRASH_DUMP
+	if (test_facility(129))
+		save_vx_regs(boot_cpu_vector_save_area);
+#endif
+}
+
 static int __init disable_vector_extension(char *str)
 {
 	S390_lowcore.machine_flags &= ~MACHINE_FLAG_VX;
@@ -451,6 +459,7 @@ void __init startup_init(void)
 	detect_diag9c();
 	detect_diag44();
 	detect_machine_facilities();
+	save_vector_registers();
 	setup_topology();
 	sclp_early_detect();
 	lockdep_on();

arch/s390/kernel/ipl.c

@@ -2039,10 +2039,7 @@ static void do_reset_calls(void)
 		reset->fn();
 }
 
-u32 dump_prefix_page;
-
-void s390_reset_system(void (*fn_pre)(void),
-		       void (*fn_post)(void *), void *data)
+void s390_reset_system(void)
 {
 	struct _lowcore *lc;
 
@@ -2051,9 +2048,6 @@ void s390_reset_system(void (*fn_pre)(void),
 	/* Stack for interrupt/machine check handler */
 	lc->panic_stack = S390_lowcore.panic_stack;
 
-	/* Save prefix page address for dump case */
-	dump_prefix_page = (u32)(unsigned long) lc;
-
 	/* Disable prefixing */
 	set_prefix(0);
 
@@ -2077,14 +2071,5 @@ void s390_reset_system(void (*fn_pre)(void),
 	S390_lowcore.subchannel_id = 0;
 	S390_lowcore.subchannel_nr = 0;
 
-	/* Store status at absolute zero */
-	store_status();
-
-	/* Call function before reset */
-	if (fn_pre)
-		fn_pre();
 	do_reset_calls();
-	/* Call function after reset */
-	if (fn_post)
-		fn_post(data);
 }

arch/s390/kernel/machine_kexec.c

@@ -34,40 +34,6 @@ extern const unsigned long long relocate_kernel_len;
 
 #ifdef CONFIG_CRASH_DUMP
 
-/*
- * Initialize CPU ELF notes
- */
-static void setup_regs(void)
-{
-	struct save_area *sa, *sa_0;
-	unsigned long prefix;
-	int cpu, this_cpu;
-
-	/* setup_regs is called with the prefix register = 0 */
-	sa_0 = (struct save_area *) __LC_FPREGS_SAVE_AREA;
-
-	/* Get status of this CPU out of absolute zero */
-	prefix = (unsigned long) S390_lowcore.prefixreg_save_area;
-	sa = (struct save_area *)(prefix + __LC_FPREGS_SAVE_AREA);
-	memcpy(sa, sa_0, sizeof(struct save_area));
-	if (MACHINE_HAS_VX) {
-		struct _lowcore *lc = (struct _lowcore *) prefix;
-		save_vx_regs_safe((void *) lc->vector_save_area_addr);
-	}
-
-	/* Get status of the other CPUs */
-	this_cpu = smp_find_processor_id(stap());
-	for_each_online_cpu(cpu) {
-		if (cpu == this_cpu)
-			continue;
-		if (smp_store_status(cpu))
-			continue;
-		prefix = (unsigned long) S390_lowcore.prefixreg_save_area;
-		sa = (struct save_area *)(prefix + __LC_FPREGS_SAVE_AREA);
-		memcpy(sa, sa_0, sizeof(struct save_area));
-	}
-}
-
 /*
  * PM notifier callback for kdump
  */
@@ -99,14 +65,66 @@ static int __init machine_kdump_pm_init(void)
 arch_initcall(machine_kdump_pm_init);
 
 /*
- * Start kdump: We expect here that a store status has been done on our CPU
+ * Reset the system, copy boot CPU registers to absolute zero,
+ * and jump to the kdump image
  */
 static void __do_machine_kdump(void *image)
 {
-	int (*start_kdump)(int) = (void *)((struct kimage *) image)->start;
+	int (*start_kdump)(int);
+	unsigned long prefix;
+
+	/* store_status() saved the prefix register to lowcore */
+	prefix = (unsigned long) S390_lowcore.prefixreg_save_area;
+
+	/* Now do the reset  */
+	s390_reset_system();
+
+	/*
+	 * Copy dump CPU store status info to absolute zero.
+	 * This need to be done *after* s390_reset_system set the
+	 * prefix register of this CPU to zero
+	 */
+	memcpy((void *) __LC_FPREGS_SAVE_AREA,
+	       (void *)(prefix + __LC_FPREGS_SAVE_AREA), 512);
 
 	__load_psw_mask(PSW_MASK_BASE | PSW_DEFAULT_KEY | PSW_MASK_EA | PSW_MASK_BA);
+	start_kdump = (void *)((struct kimage *) image)->start;
 	start_kdump(1);
+
+	/* Die if start_kdump returns */
+	disabled_wait((unsigned long) __builtin_return_address(0));
+}
+
+/*
+ * Start kdump: create a LGR log entry, store status of all CPUs and
+ * branch to __do_machine_kdump.
+ */
+static noinline void __machine_kdump(void *image)
+{
+	int this_cpu, cpu;
+
+	lgr_info_log();
+	/* Get status of the other CPUs */
+	this_cpu = smp_find_processor_id(stap());
+	for_each_online_cpu(cpu) {
+		if (cpu == this_cpu)
+			continue;
+		if (smp_store_status(cpu))
+			continue;
+	}
+	/* Store status of the boot CPU */
+	if (MACHINE_HAS_VX)
+		save_vx_regs((void *) &S390_lowcore.vector_save_area);
+	/*
+	 * To create a good backchain for this CPU in the dump store_status
+	 * is passed the address of a function. The address is saved into
+	 * the PSW save area of the boot CPU and the function is invoked as
+	 * a tail call of store_status. The backchain in the dump will look
+	 * like this:
+	 *   restart_int_handler ->  __machine_kexec -> __do_machine_kdump
+	 * The call to store_status() will not return.
+	 */
+	store_status(__do_machine_kdump, image);
 }
 #endif
 
@@ -229,10 +247,14 @@ static void __do_machine_kexec(void *data)
 	relocate_kernel_t data_mover;
 	struct kimage *image = data;
 
+	s390_reset_system();
 	data_mover = (relocate_kernel_t) page_to_phys(image->control_code_page);
 
 	/* Call the moving routine */
 	(*data_mover)(&image->head, image->start);
+
+	/* Die if kexec returns */
+	disabled_wait((unsigned long) __builtin_return_address(0));
 }
 
 /*
@@ -245,14 +267,10 @@ static void __machine_kexec(void *data)
 	tracing_off();
 	debug_locks_off();
 #ifdef CONFIG_CRASH_DUMP
-	if (((struct kimage *) data)->type == KEXEC_TYPE_CRASH) {
-
-		lgr_info_log();
-		s390_reset_system(setup_regs, __do_machine_kdump, data);
-	} else
+	if (((struct kimage *) data)->type == KEXEC_TYPE_CRASH)
+		__machine_kdump(data);
 #endif
-		s390_reset_system(NULL, __do_machine_kexec, data);
-	disabled_wait((unsigned long) __builtin_return_address(0));
+	__do_machine_kexec(data);
 }
 
 /*

arch/s390/kernel/reipl.S

@@ -9,12 +9,11 @@
 #include <asm/sigp.h>
 
 #
-# store_status
+# Issue "store status" for the current CPU to its prefix page
+# and call passed function afterwards
 #
-# Prerequisites to run this function:
-# - Prefix register is set to zero
-# - Original prefix register is stored in "dump_prefix_page"
-# - Lowcore protection is off
+# r2 = Function to be called after store status
+# r3 = Parameter for function
 #
 ENTRY(store_status)
 	/* Save register one and load save area base */
@@ -53,23 +52,23 @@ ENTRY(store_status)
 	/* CPU timer */
 	lghi	%r1,__LC_CPU_TIMER_SAVE_AREA
 	stpt	0(%r1)
-	/* Saved prefix register */
+	/* Store prefix register */
 	lghi	%r1,__LC_PREFIX_SAVE_AREA
-	larl	%r2,dump_prefix_page
-	mvc	0(4,%r1),0(%r2)
+	stpx	0(%r1)
 	/* Clock comparator - seven bytes */
 	lghi	%r1,__LC_CLOCK_COMP_SAVE_AREA
-	larl	%r2,.Lclkcmp
-	stckc	0(%r2)
-	mvc	1(7,%r1),1(%r2)
+	larl	%r4,.Lclkcmp
+	stckc	0(%r4)
+	mvc	1(7,%r1),1(%r4)
 	/* Program status word */
 	lghi	%r1,__LC_PSW_SAVE_AREA
-	epsw	%r2,%r3
-	st	%r2,0(%r1)
-	st	%r3,4(%r1)
-	larl	%r2,store_status
+	epsw	%r4,%r5
+	st	%r4,0(%r1)
+	st	%r5,4(%r1)
 	stg	%r2,8(%r1)
-	br	%r14
+	lgr	%r1,%r2
+	lgr	%r2,%r3
+	br	%r1
 
 	.section .bss
 	.align	8
@@ -84,9 +83,11 @@ ENTRY(store_status)
 ENTRY(do_reipl_asm)
 		basr	%r13,0
 .Lpg0:		lpswe	.Lnewpsw-.Lpg0(%r13)
-.Lpg1:		brasl	%r14,store_status
+.Lpg1:		lgr	%r3,%r2
+		larl	%r2,.Lstatus
+		brasl	%r14,store_status
 
-		lctlg	%c6,%c6,.Lall-.Lpg0(%r13)
+.Lstatus:	lctlg	%c6,%c6,.Lall-.Lpg0(%r13)
 		lgr	%r1,%r2
 		mvc	__LC_PGM_NEW_PSW(16),.Lpcnew-.Lpg0(%r13)
 		stsch	.Lschib-.Lpg0(%r13)

arch/s390/kernel/setup.c

@@ -865,11 +865,13 @@ void __init setup_arch(char **cmdline_p)
 
 	check_initrd();
 	reserve_crashkernel();
+#ifdef CONFIG_CRASH_DUMP
 	/*
 	 * Be aware that smp_save_dump_cpus() triggers a system reset.
 	 * Therefore CPU and device initialization should be done afterwards.
 	 */
 	smp_save_dump_cpus();
+#endif
 
 	setup_resources();
 	setup_vmcoreinfo();