s390/time: add support for the TOD clock epoch extension

The TOD epoch extension adds 8 epoch bits to the TOD clock to provide
a continuous clock after 2042/09/17. The store-clock-extended (STCKE)
instruction will store the epoch index in the first byte of the
16 bytes stored by the instruction. The read_boot_clock64 and the
read_presistent_clock64 functions need to take the additional bits
into account to give the correct result after 2042/09/17.

The clock-comparator register will stay 64 bit wide. The comparison
of the clock-comparator with the TOD clock is limited to bytes
1 to 8 of the extended TOD format. To deal with the overflow problem
due to an epoch change the clock-comparator sign control in CR0 can
be used to switch the comparison of the 64-bit TOD clock with the
clock-comparator to a signed comparison.

The decision between the signed vs. unsigned clock-comparator
comparisons is done at boot time. Only if the TOD clock is in the
second half of a 142 year epoch the signed comparison is used.
This solves the epoch overflow issue as long as the machine is
booted at least once in an epoch.

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

3 files changed, 60 insertions, 28 deletions

diff --git a/arch/s390/include/asm/lowcore.h b/arch/s390/include/asm/lowcore.h
index 8a5b082797f8..a6870ea6ea8b 100644
--- a/arch/s390/include/asm/lowcore.h
+++ b/arch/s390/include/asm/lowcore.h
@@ -95,46 +95,46 @@ struct lowcore {
 	__u64	int_clock;			/* 0x0310 */
 	__u64	mcck_clock;			/* 0x0318 */
 	__u64	clock_comparator;		/* 0x0320 */
+	__u64	boot_clock[2];			/* 0x0328 */
 
 	/* Current process. */
-	__u64	current_task;			/* 0x0328 */
-	__u8	pad_0x318[0x320-0x318];		/* 0x0330 */
-	__u64	kernel_stack;			/* 0x0338 */
+	__u64	current_task;			/* 0x0338 */
+	__u64	kernel_stack;			/* 0x0340 */
 
 	/* Interrupt, panic and restart stack. */
-	__u64	async_stack;			/* 0x0340 */
-	__u64	panic_stack;			/* 0x0348 */
-	__u64	restart_stack;			/* 0x0350 */
+	__u64	async_stack;			/* 0x0348 */
+	__u64	panic_stack;			/* 0x0350 */
+	__u64	restart_stack;			/* 0x0358 */
 
 	/* Restart function and parameter. */
-	__u64	restart_fn;			/* 0x0358 */
-	__u64	restart_data;			/* 0x0360 */
-	__u64	restart_source;			/* 0x0368 */
+	__u64	restart_fn;			/* 0x0360 */
+	__u64	restart_data;			/* 0x0368 */
+	__u64	restart_source;			/* 0x0370 */
 
 	/* Address space pointer. */
-	__u64	kernel_asce;			/* 0x0370 */
-	__u64	user_asce;			/* 0x0378 */
+	__u64	kernel_asce;			/* 0x0378 */
+	__u64	user_asce;			/* 0x0380 */
 
 	/*
 	 * The lpp and current_pid fields form a
 	 * 64-bit value that is set as program
 	 * parameter with the LPP instruction.
 	 */
-	__u32	lpp;				/* 0x0380 */
-	__u32	current_pid;			/* 0x0384 */
+	__u32	lpp;				/* 0x0388 */
+	__u32	current_pid;			/* 0x038c */
 
 	/* SMP info area */
-	__u32	cpu_nr;				/* 0x0388 */
-	__u32	softirq_pending;		/* 0x038c */
-	__u64	percpu_offset;			/* 0x0390 */
-	__u64	vdso_per_cpu_data;		/* 0x0398 */
-	__u64	machine_flags;			/* 0x03a0 */
-	__u32	preempt_count;			/* 0x03a8 */
-	__u8	pad_0x03ac[0x03b0-0x03ac];	/* 0x03ac */
-	__u64	gmap;				/* 0x03b0 */
-	__u32	spinlock_lockval;		/* 0x03b8 */
-	__u32	fpu_flags;			/* 0x03bc */
-	__u8	pad_0x03c0[0x0400-0x03c0];	/* 0x03c0 */
+	__u32	cpu_nr;				/* 0x0390 */
+	__u32	softirq_pending;		/* 0x0394 */
+	__u64	percpu_offset;			/* 0x0398 */
+	__u64	vdso_per_cpu_data;		/* 0x03a0 */
+	__u64	machine_flags;			/* 0x03a8 */
+	__u32	preempt_count;			/* 0x03b0 */
+	__u8	pad_0x03b4[0x03b8-0x03b4];	/* 0x03b4 */
+	__u64	gmap;				/* 0x03b8 */
+	__u32	spinlock_lockval;		/* 0x03c0 */
+	__u32	fpu_flags;			/* 0x03c4 */
+	__u8	pad_0x03c8[0x0400-0x03c8];	/* 0x03c8 */
 
 	/* Per cpu primary space access list */
 	__u32	paste[16];			/* 0x0400 */
diff --git a/arch/s390/include/asm/setup.h b/arch/s390/include/asm/setup.h
index 49c425903894..61da4bd6edad 100644
--- a/arch/s390/include/asm/setup.h
+++ b/arch/s390/include/asm/setup.h
@@ -32,6 +32,7 @@
 #define MACHINE_FLAG_TLB_GUEST	_BITUL(14)
 #define MACHINE_FLAG_NX		_BITUL(15)
 #define MACHINE_FLAG_GS		_BITUL(16)
+#define MACHINE_FLAG_SCC	_BITUL(17)
 
 #define LPP_MAGIC		_BITUL(31)
 #define LPP_PFAULT_PID_MASK	_AC(0xffffffff, UL)
@@ -72,6 +73,7 @@ extern void detect_memory_memblock(void);
 #define MACHINE_HAS_TLB_GUEST	(S390_lowcore.machine_flags & MACHINE_FLAG_TLB_GUEST)
 #define MACHINE_HAS_NX		(S390_lowcore.machine_flags & MACHINE_FLAG_NX)
 #define MACHINE_HAS_GS		(S390_lowcore.machine_flags & MACHINE_FLAG_GS)
+#define MACHINE_HAS_SCC		(S390_lowcore.machine_flags & MACHINE_FLAG_SCC)
 
 /*
  * Console mode. Override with conmode=
diff --git a/arch/s390/include/asm/timex.h b/arch/s390/include/asm/timex.h
index 118535123f34..0ea03c11458d 100644
--- a/arch/s390/include/asm/timex.h
+++ b/arch/s390/include/asm/timex.h
@@ -15,6 +15,8 @@
 /* The value of the TOD clock for 1.1.1970. */
 #define TOD_UNIX_EPOCH 0x7d91048bca000000ULL
 
+extern u64 clock_comparator_max;
+
 /* Inline functions for clock register access. */
 static inline int set_tod_clock(__u64 time)
 {
@@ -126,7 +128,7 @@ static inline unsigned long long local_tick_disable(void)
 	unsigned long long old;
 
 	old = S390_lowcore.clock_comparator;
-	S390_lowcore.clock_comparator = -1ULL;
+	S390_lowcore.clock_comparator = clock_comparator_max;
 	set_clock_comparator(S390_lowcore.clock_comparator);
 	return old;
 }
@@ -178,20 +180,20 @@ int get_phys_clock(unsigned long long *clock);
 void init_cpu_timer(void);
 unsigned long long monotonic_clock(void);
 
-extern u64 sched_clock_base_cc;
+extern unsigned char tod_clock_base[16] __aligned(8);
 
 /**
  * get_clock_monotonic - returns current time in clock rate units
  *
  * The caller must ensure that preemption is disabled.
- * The clock and sched_clock_base get changed via stop_machine.
+ * The clock and tod_clock_base get changed via stop_machine.
  * Therefore preemption must be disabled when calling this
  * function, otherwise the returned value is not guaranteed to
  * be monotonic.
  */
 static inline unsigned long long get_tod_clock_monotonic(void)
 {
-	return get_tod_clock() - sched_clock_base_cc;
+	return get_tod_clock() - *(unsigned long long *) &tod_clock_base[1];
 }
 
 /**
@@ -218,4 +220,32 @@ static inline unsigned long long tod_to_ns(unsigned long long todval)
 	return ((todval >> 9) * 125) + (((todval & 0x1ff) * 125) >> 9);
 }
 
+/**
+ * tod_after - compare two 64 bit TOD values
+ * @a: first 64 bit TOD timestamp
+ * @b: second 64 bit TOD timestamp
+ *
+ * Returns: true if a is later than b
+ */
+static inline int tod_after(unsigned long long a, unsigned long long b)
+{
+	if (MACHINE_HAS_SCC)
+		return (long long) a > (long long) b;
+	return a > b;
+}
+
+/**
+ * tod_after_eq - compare two 64 bit TOD values
+ * @a: first 64 bit TOD timestamp
+ * @b: second 64 bit TOD timestamp
+ *
+ * Returns: true if a is later than b
+ */
+static inline int tod_after_eq(unsigned long long a, unsigned long long b)
+{
+	if (MACHINE_HAS_SCC)
+		return (long long) a >= (long long) b;
+	return a >= b;
+}
+
 #endif