[S390] idle time accounting vs. machine checks

A machine check can interrupt the i/o and external interrupt handler
anytime. If the machine check occurs while the interrupt handler is
waking up from idle vtime_start_cpu can get executed a second time
and the int_clock / async_enter_timer values in the lowcore get
clobbered. This can confuse the cpu time accounting.
To fix this problem two changes are needed. First the machine check
handler has to use its own copies of int_clock and async_enter_timer,
named mcck_clock and mcck_enter_timer. Second the nested execution
of vtime_start_cpu has to be prevented. This is done in s390_idle_check
by checking the wait bit in the program status word.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 56 insertions, 51 deletions

diff --git a/arch/s390/include/asm/cputime.h b/arch/s390/include/asm/cputime.h
index 258ba88b7b50..8b1a52a137c5 100644
--- a/arch/s390/include/asm/cputime.h
+++ b/arch/s390/include/asm/cputime.h
@@ -188,15 +188,16 @@ struct s390_idle_data {
 
 DECLARE_PER_CPU(struct s390_idle_data, s390_idle);
 
-void vtime_start_cpu(void);
+void vtime_start_cpu(__u64 int_clock, __u64 enter_timer);
 cputime64_t s390_get_idle_time(int cpu);
 
 #define arch_idle_time(cpu) s390_get_idle_time(cpu)
 
-static inline void s390_idle_check(void)
+static inline void s390_idle_check(struct pt_regs *regs, __u64 int_clock,
+                                   __u64 enter_timer)
 {
-        if ((&__get_cpu_var(s390_idle))->idle_enter != 0ULL)
-                vtime_start_cpu();
+        if (regs->psw.mask & PSW_MASK_WAIT)
+                vtime_start_cpu(int_clock, enter_timer);
 }
 
 static inline int s390_nohz_delay(int cpu)
diff --git a/arch/s390/include/asm/lowcore.h b/arch/s390/include/asm/lowcore.h
index f7e78c79b8b1..2c02d46c3588 100644
--- a/arch/s390/include/asm/lowcore.h
+++ b/arch/s390/include/asm/lowcore.h
@@ -104,37 +104,39 @@ struct _lowcore {
         /* CPU time accounting values */
         __u64   sync_enter_timer;               /* 0x0250 */
         __u64   async_enter_timer;              /* 0x0258 */
-        __u64   exit_timer;                     /* 0x0260 */
-        __u64   user_timer;                     /* 0x0268 */
-        __u64   system_timer;                   /* 0x0270 */
-        __u64   steal_timer;                    /* 0x0278 */
-        __u64   last_update_timer;              /* 0x0280 */
-        __u64   last_update_clock;              /* 0x0288 */
+        __u64   mcck_enter_timer;               /* 0x0260 */
+        __u64   exit_timer;                     /* 0x0268 */
+        __u64   user_timer;                     /* 0x0270 */
+        __u64   system_timer;                   /* 0x0278 */
+        __u64   steal_timer;                    /* 0x0280 */
+        __u64   last_update_timer;              /* 0x0288 */
+        __u64   last_update_clock;              /* 0x0290 */
 
         /* Current process. */
-        __u32   current_task;                   /* 0x0290 */
-        __u32   thread_info;                    /* 0x0294 */
-        __u32   kernel_stack;                   /* 0x0298 */
+        __u32   current_task;                   /* 0x0298 */
+        __u32   thread_info;                    /* 0x029c */
+        __u32   kernel_stack;                   /* 0x02a0 */
 
         /* Interrupt and panic stack. */
-        __u32   async_stack;                    /* 0x029c */
-        __u32   panic_stack;                    /* 0x02a0 */
+        __u32   async_stack;                    /* 0x02a4 */
+        __u32   panic_stack;                    /* 0x02a8 */
 
         /* Address space pointer. */
-        __u32   kernel_asce;                    /* 0x02a4 */
-        __u32   user_asce;                      /* 0x02a8 */
-        __u32   user_exec_asce;                 /* 0x02ac */
+        __u32   kernel_asce;                    /* 0x02ac */
+        __u32   user_asce;                      /* 0x02b0 */
+        __u32   user_exec_asce;                 /* 0x02b4 */
 
         /* SMP info area */
-        __u32   cpu_nr;                         /* 0x02b0 */
-        __u32   softirq_pending;                /* 0x02b4 */
-        __u32   percpu_offset;                  /* 0x02b8 */
-        __u32   ext_call_fast;                  /* 0x02bc */
-        __u64   int_clock;                      /* 0x02c0 */
-        __u64   clock_comparator;               /* 0x02c8 */
-        __u32   machine_flags;                  /* 0x02d0 */
-        __u32   ftrace_func;                    /* 0x02d4 */
-        __u8    pad_0x02d8[0x0300-0x02d8];      /* 0x02d8 */
+        __u32   cpu_nr;                         /* 0x02b8 */
+        __u32   softirq_pending;                /* 0x02bc */
+        __u32   percpu_offset;                  /* 0x02c0 */
+        __u32   ext_call_fast;                  /* 0x02c4 */
+        __u64   int_clock;                      /* 0x02c8 */
+        __u64   mcck_clock;                     /* 0x02d0 */
+        __u64   clock_comparator;               /* 0x02d8 */
+        __u32   machine_flags;                  /* 0x02e0 */
+        __u32   ftrace_func;                    /* 0x02e4 */
+        __u8    pad_0x02e8[0x0300-0x02e8];      /* 0x02e8 */
 
         /* Interrupt response block */
         __u8    irb[64];                        /* 0x0300 */
@@ -232,38 +234,40 @@ struct _lowcore {
         /* CPU accounting and timing values. */
         __u64   sync_enter_timer;               /* 0x02a0 */
         __u64   async_enter_timer;              /* 0x02a8 */
-        __u64   exit_timer;                     /* 0x02b0 */
-        __u64   user_timer;                     /* 0x02b8 */
-        __u64   system_timer;                   /* 0x02c0 */
-        __u64   steal_timer;                    /* 0x02c8 */
-        __u64   last_update_timer;              /* 0x02d0 */
-        __u64   last_update_clock;              /* 0x02d8 */
+        __u64   mcck_enter_timer;               /* 0x02b0 */
+        __u64   exit_timer;                     /* 0x02b8 */
+        __u64   user_timer;                     /* 0x02c0 */
+        __u64   system_timer;                   /* 0x02c8 */
+        __u64   steal_timer;                    /* 0x02d0 */
+        __u64   last_update_timer;              /* 0x02d8 */
+        __u64   last_update_clock;              /* 0x02e0 */
 
         /* Current process. */
-        __u64   current_task;                   /* 0x02e0 */
-        __u64   thread_info;                    /* 0x02e8 */
-        __u64   kernel_stack;                   /* 0x02f0 */
+        __u64   current_task;                   /* 0x02e8 */
+        __u64   thread_info;                    /* 0x02f0 */
+        __u64   kernel_stack;                   /* 0x02f8 */
 
         /* Interrupt and panic stack. */
-        __u64   async_stack;                    /* 0x02f8 */
-        __u64   panic_stack;                    /* 0x0300 */
+        __u64   async_stack;                    /* 0x0300 */
+        __u64   panic_stack;                    /* 0x0308 */
 
         /* Address space pointer. */
-        __u64   kernel_asce;                    /* 0x0308 */
-        __u64   user_asce;                      /* 0x0310 */
-        __u64   user_exec_asce;                 /* 0x0318 */
+        __u64   kernel_asce;                    /* 0x0310 */
+        __u64   user_asce;                      /* 0x0318 */
+        __u64   user_exec_asce;                 /* 0x0320 */
 
         /* SMP info area */
-        __u32   cpu_nr;                         /* 0x0320 */
-        __u32   softirq_pending;                /* 0x0324 */
-        __u64   percpu_offset;                  /* 0x0328 */
-        __u64   ext_call_fast;                  /* 0x0330 */
-        __u64   int_clock;                      /* 0x0338 */
-        __u64   clock_comparator;               /* 0x0340 */
-        __u64   vdso_per_cpu_data;              /* 0x0348 */
-        __u64   machine_flags;                  /* 0x0350 */
-        __u64   ftrace_func;                    /* 0x0358 */
-        __u8    pad_0x0368[0x0380-0x0360];      /* 0x0360 */
+        __u32   cpu_nr;                         /* 0x0328 */
+        __u32   softirq_pending;                /* 0x032c */
+        __u64   percpu_offset;                  /* 0x0330 */
+        __u64   ext_call_fast;                  /* 0x0338 */
+        __u64   int_clock;                      /* 0x0340 */
+        __u64   mcck_clock;                     /* 0x0348 */
+        __u64   clock_comparator;               /* 0x0350 */
+        __u64   vdso_per_cpu_data;              /* 0x0358 */
+        __u64   machine_flags;                  /* 0x0360 */
+        __u64   ftrace_func;                    /* 0x0368 */
+        __u8    pad_0x0370[0x0380-0x0370];      /* 0x0370 */
 
         /* Interrupt response block. */
         __u8    irb[64];                        /* 0x0380 */