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, 9 insertions, 1 deletions

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index a5781404b83f..b277d50dcf76 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -71,9 +71,13 @@ static int ckc_interrupts_enabled(struct kvm_vcpu *vcpu)
 
 static int ckc_irq_pending(struct kvm_vcpu *vcpu)
 {
+        preempt_disable();
         if (!(vcpu->arch.sie_block->ckc <
-              get_tod_clock_fast() + vcpu->arch.sie_block->epoch))
+              get_tod_clock_fast() + vcpu->arch.sie_block->epoch)) {
+                preempt_enable();
                 return 0;
+        }
+        preempt_enable();
         return ckc_interrupts_enabled(vcpu);
 }
 
@@ -856,7 +860,9 @@ int kvm_s390_handle_wait(struct kvm_vcpu *vcpu)
                 goto no_timer;
         }
 
+        preempt_disable();
         now = get_tod_clock_fast() + vcpu->arch.sie_block->epoch;
+        preempt_enable();
         sltime = tod_to_ns(vcpu->arch.sie_block->ckc - now);
 
         /* underflow */
@@ -895,7 +901,9 @@ enum hrtimer_restart kvm_s390_idle_wakeup(struct hrtimer *timer)
         u64 now, sltime;
 
         vcpu = container_of(timer, struct kvm_vcpu, arch.ckc_timer);
+        preempt_disable();
         now = get_tod_clock_fast() + vcpu->arch.sie_block->epoch;
+        preempt_enable();
         sltime = tod_to_ns(vcpu->arch.sie_block->ckc - now);
 
         /*