KVM: s390: host STP toleration for VMs

If the host has STP enabled, the TOD of the host will be changed during
synchronization phases. These are performed during a stop_machine() call.

As the guest TOD is based on the host TOD, we have to make sure that:
- no VCPU is in the SIE (implicitly guaranteed via stop_machine())
- manual guest TOD calculations are not affected

"Epoch" is the guest TOD clock delta to the host TOD clock. We have to
adjust that value during the STP synchronization and make sure that code
that accesses the epoch won't get interrupted in between (via disabling
preemption).

Signed-off-by: Fan Zhang <zhangfan@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 13 insertions, 3 deletions

diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index 9e733d965e08..627887b075a7 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -58,6 +58,9 @@ EXPORT_SYMBOL_GPL(sched_clock_base_cc);
 
 static DEFINE_PER_CPU(struct clock_event_device, comparators);
 
+ATOMIC_NOTIFIER_HEAD(s390_epoch_delta_notifier);
+EXPORT_SYMBOL(s390_epoch_delta_notifier);
+
 /*
  * Scheduler clock - returns current time in nanosec units.
  */
@@ -752,7 +755,7 @@ static void clock_sync_cpu(struct clock_sync_data *sync)
 static int etr_sync_clock(void *data)
 {
         static int first;
-        unsigned long long clock, old_clock, delay, delta;
+        unsigned long long clock, old_clock, clock_delta, delay, delta;
         struct clock_sync_data *etr_sync;
         struct etr_aib *sync_port, *aib;
         int port;
@@ -789,6 +792,9 @@ static int etr_sync_clock(void *data)
                 delay = (unsigned long long)
                         (aib->edf2.etv - sync_port->edf2.etv) << 32;
                 delta = adjust_time(old_clock, clock, delay);
+                clock_delta = clock - old_clock;
+                atomic_notifier_call_chain(&s390_epoch_delta_notifier, 0,
+                                           &clock_delta);
                 etr_sync->fixup_cc = delta;
                 fixup_clock_comparator(delta);
                 /* Verify that the clock is properly set. */
@@ -1526,7 +1532,7 @@ void stp_island_check(void)
 static int stp_sync_clock(void *data)
 {
         static int first;
-        unsigned long long old_clock, delta;
+        unsigned long long old_clock, delta, new_clock, clock_delta;
         struct clock_sync_data *stp_sync;
         int rc;
 
@@ -1551,7 +1557,11 @@ static int stp_sync_clock(void *data)
                 old_clock = get_tod_clock();
                 rc = chsc_sstpc(stp_page, STP_OP_SYNC, 0);
                 if (rc == 0) {
-                        delta = adjust_time(old_clock, get_tod_clock(), 0);
+                        new_clock = get_tod_clock();
+                        delta = adjust_time(old_clock, new_clock, 0);
+                        clock_delta = new_clock - old_clock;
+                        atomic_notifier_call_chain(&s390_epoch_delta_notifier,
+                                                   0, &clock_delta);
                         fixup_clock_comparator(delta);
                         rc = chsc_sstpi(stp_page, &stp_info,
                                         sizeof(struct stp_sstpi));