s390/time: LPAR offset handling

It is possible to specify a user offset for the TOD clock, e.g. +2 hours.
The TOD clock will carry this offset even if the clock is synchronized
with STP. This makes the time stamps acquired with get_sync_clock()
useless as another LPAR migth use a different TOD offset.

Use the PTFF instrution to get the TOD epoch difference and subtract
it from the TOD clock value to get a physical timestamp. As the epoch
difference contains the sync check delta as well the LPAR offset value
to the physical clock needs to be refreshed after each clock
synchronization.

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

4 files changed, 55 insertions, 11 deletions

diff --git a/arch/s390/include/asm/timex.h b/arch/s390/include/asm/timex.h
index 920db0a2496b..0f34db4238da 100644
--- a/arch/s390/include/asm/timex.h
+++ b/arch/s390/include/asm/timex.h
@@ -52,6 +52,11 @@ static inline void store_clock_comparator(__u64 *time)
 
 void clock_comparator_work(void);
 
+void __init ptff_init(void);
+
+extern unsigned char ptff_function_mask[16];
+extern unsigned long lpar_offset;
+
 /* Function codes for the ptff instruction. */
 #define PTFF_QAF	0x00	/* query available functions */
 #define PTFF_QTO	0x01	/* query tod offset */
@@ -69,6 +74,14 @@ struct ptff_qto {
 	unsigned long long tod_epoch_difference;
 } __packed;
 
+static inline int ptff_query(unsigned int nr)
+{
+	unsigned char *ptr;
+
+	ptr = ptff_function_mask + (nr >> 3);
+	return (*ptr & (0x80 >> (nr & 7))) != 0;
+}
+
 static inline int ptff(void *ptff_block, size_t len, unsigned int func)
 {
 	typedef struct { char _[len]; } addrtype;
@@ -138,7 +151,7 @@ static inline cycles_t get_cycles(void)
 	return (cycles_t) get_tod_clock() >> 2;
 }
 
-int get_sync_clock(unsigned long long *clock);
+int get_phys_clock(unsigned long long *clock);
 void init_cpu_timer(void);
 unsigned long long monotonic_clock(void);
 
diff --git a/arch/s390/kernel/early.c b/arch/s390/kernel/early.c
index 4067dbe390ac..717b03aa16b5 100644
--- a/arch/s390/kernel/early.c
+++ b/arch/s390/kernel/early.c
@@ -467,6 +467,7 @@ void __init startup_init(void)
 	ipl_save_parameters();
 	rescue_initrd();
 	clear_bss_section();
+	ptff_init();
 	init_kernel_storage_key();
 	lockdep_off();
 	setup_lowcore_early();
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index a725fd1c4315..d71623639997 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -39,6 +39,7 @@
 #include <linux/gfp.h>
 #include <linux/kprobes.h>
 #include <asm/uaccess.h>
+#include <asm/facility.h>
 #include <asm/delay.h>
 #include <asm/div64.h>
 #include <asm/vdso.h>
@@ -61,6 +62,25 @@ static DEFINE_PER_CPU(struct clock_event_device, comparators);
 ATOMIC_NOTIFIER_HEAD(s390_epoch_delta_notifier);
 EXPORT_SYMBOL(s390_epoch_delta_notifier);
 
+unsigned char ptff_function_mask[16];
+unsigned long lpar_offset;
+
+/*
+ * Get time offsets with PTFF
+ */
+void __init ptff_init(void)
+{
+	struct ptff_qto qto;
+
+	if (!test_facility(28))
+		return;
+	ptff(&ptff_function_mask, sizeof(ptff_function_mask), PTFF_QAF);
+
+	/* get LPAR offset */
+	if (ptff_query(PTFF_QTO) && ptff(&qto, sizeof(qto), PTFF_QTO) == 0)
+		lpar_offset = qto.tod_epoch_difference;
+}
+
 /*
  * Scheduler clock - returns current time in nanosec units.
  */
@@ -337,20 +357,20 @@ static unsigned long clock_sync_flags;
 #define CLOCK_SYNC_STP		3
 
 /*
- * The synchronous get_clock function. It will write the current clock
- * value to the clock pointer and return 0 if the clock is in sync with
- * the external time source. If the clock mode is local it will return
- * -EOPNOTSUPP and -EAGAIN if the clock is not in sync with the external
- * reference.
+ * The get_clock function for the physical clock. It will get the current
+ * TOD clock, subtract the LPAR offset and write the result to *clock.
+ * The function returns 0 if the clock is in sync with the external time
+ * source. If the clock mode is local it will return -EOPNOTSUPP and
+ * -EAGAIN if the clock is not in sync with the external reference.
  */
-int get_sync_clock(unsigned long long *clock)
+int get_phys_clock(unsigned long long *clock)
 {
 	atomic_t *sw_ptr;
 	unsigned int sw0, sw1;
 
 	sw_ptr = &get_cpu_var(clock_sync_word);
 	sw0 = atomic_read(sw_ptr);
-	*clock = get_tod_clock();
+	*clock = get_tod_clock() - lpar_offset;
 	sw1 = atomic_read(sw_ptr);
 	put_cpu_var(clock_sync_word);
 	if (sw0 == sw1 && (sw0 & 0x80000000U))
@@ -364,7 +384,7 @@ int get_sync_clock(unsigned long long *clock)
 		return -EACCES;
 	return -EAGAIN;
 }
-EXPORT_SYMBOL(get_sync_clock);
+EXPORT_SYMBOL(get_phys_clock);
 
 /*
  * Make get_sync_clock return -EAGAIN.
@@ -758,6 +778,7 @@ static int etr_sync_clock(void *data)
 	unsigned long long clock, old_clock, clock_delta, delay, delta;
 	struct clock_sync_data *etr_sync;
 	struct etr_aib *sync_port, *aib;
+	struct ptff_qto qto;
 	int port;
 	int rc;
 
@@ -804,6 +825,10 @@ static int etr_sync_clock(void *data)
 			etr_sync->in_sync = -EAGAIN;
 			rc = -EAGAIN;
 		} else {
+			if (ptff_query(PTFF_QTO) &&
+			    ptff(&qto, sizeof(qto), PTFF_QTO) == 0)
+				/* Update LPAR offset */
+				lpar_offset = qto.tod_epoch_difference;
 			etr_sync->in_sync = 1;
 			rc = 0;
 		}
@@ -1533,6 +1558,7 @@ static int stp_sync_clock(void *data)
 	static int first;
 	unsigned long long old_clock, delta, new_clock, clock_delta;
 	struct clock_sync_data *stp_sync;
+	struct ptff_qto qto;
 	int rc;
 
 	stp_sync = data;
@@ -1558,6 +1584,10 @@ static int stp_sync_clock(void *data)
 		if (rc == 0) {
 			new_clock = old_clock + clock_delta;
 			delta = adjust_time(old_clock, new_clock, 0);
+			if (ptff_query(PTFF_QTO) &&
+			    ptff(&qto, sizeof(qto), PTFF_QTO) == 0)
+				/* Update LPAR offset */
+				lpar_offset = qto.tod_epoch_difference;
 			atomic_notifier_call_chain(&s390_epoch_delta_notifier,
 						   0, &clock_delta);
 			fixup_clock_comparator(delta);
diff --git a/drivers/s390/block/dasd_eckd.c b/drivers/s390/block/dasd_eckd.c
index 42b34cd1f002..fd2eff440098 100644
--- a/drivers/s390/block/dasd_eckd.c
+++ b/drivers/s390/block/dasd_eckd.c
@@ -228,7 +228,7 @@ check_XRC (struct ccw1         *de_ccw,
 	data->ga_extended |= 0x08; /* switch on 'Time Stamp Valid'   */
 	data->ga_extended |= 0x02; /* switch on 'Extended Parameter' */
 
-	rc = get_sync_clock(&data->ep_sys_time);
+	rc = get_phys_clock(&data->ep_sys_time);
 	/* Ignore return code if sync clock is switched off. */
 	if (rc == -EOPNOTSUPP || rc == -EACCES)
 		rc = 0;
@@ -339,7 +339,7 @@ static int check_XRC_on_prefix(struct PFX_eckd_data *pfxdata,
 	pfxdata->define_extent.ga_extended |= 0x02; /* 'Extended Parameter' */
 	pfxdata->validity.time_stamp = 1;	    /* 'Time Stamp Valid'   */
 
-	rc = get_sync_clock(&pfxdata->define_extent.ep_sys_time);
+	rc = get_phys_clock(&pfxdata->define_extent.ep_sys_time);
 	/* Ignore return code if sync clock is switched off. */
 	if (rc == -EOPNOTSUPP || rc == -EACCES)
 		rc = 0;