KVM: s390: factor out reading of the guest TOD clock

Let's factor this out and always use get_tod_clock_fast() when
reading the guest TOD.

STORE CLOCK FAST does not do serialization and, therefore, might
result in some fuzziness between different processors in a way
that subsequent calls on different CPUs might have time stamps that
are earlier. This semantics is fine though for all KVM use cases.
To make it obvious that the new function has STORE CLOCK FAST
semantics we name it kvm_s390_get_tod_clock_fast.

With this patch, we only have a handful of places were we
have to care about STP sync (using preempt_disable() logic).

Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index cc15ea3a150e..1e70e00d3c5e 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -271,6 +271,16 @@ static inline void kvm_s390_vcpu_unblock_all(struct kvm *kvm)
                 kvm_s390_vcpu_unblock(vcpu);
 }
 
+static inline u64 kvm_s390_get_tod_clock_fast(struct kvm *kvm)
+{
+        u64 rc;
+
+        preempt_disable();
+        rc = get_tod_clock_fast() + kvm->arch.epoch;
+        preempt_enable();
+        return rc;
+}
+
 /**
  * kvm_s390_inject_prog_cond - conditionally inject a program check
  * @vcpu: virtual cpu