KVM: s390: interrupt: Fix single-stepping kernel-emulated instructions

Single-stepping a kernel-emulated instruction that generates an
interrupt causes GDB to land on the instruction following it instead of
the respective interrupt handler.

The reason is that kvm_handle_sie_intercept(), after injecting the
interrupt, also processes the PER event and arranges a KVM_SINGLESTEP
exit. The interrupt is not yet delivered, however, so the userspace
sees the next instruction.

Fix by avoiding the KVM_SINGLESTEP exit when there is a pending
interrupt. The next __vcpu_run() loop iteration will arrange a
KVM_SINGLESTEP exit after delivering the interrupt.

Reviewed-by: David Hildenbrand <[email protected]>
Reviewed-by: Claudio Imbrenda <[email protected]>
Signed-off-by: Ilya Leoshkevich <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Claudio Imbrenda <[email protected]>
Signed-off-by: Janosch Frank <[email protected]>

arch/s390/kvm/intercept.c

@@ -583,6 +583,19 @@ static int handle_pv_notification(struct kvm_vcpu *vcpu)
  return handle_instruction(vcpu);
 }
 
+static bool should_handle_per_ifetch(const struct kvm_vcpu *vcpu, int rc)
+{
+ /* Process PER, also if the instruction is processed in user space. */
+ if (!(vcpu->arch.sie_block->icptstatus & 0x02))
+ return false;
+ if (rc != 0 && rc != -EOPNOTSUPP)
+ return false;
+ if (guestdbg_sstep_enabled(vcpu) && vcpu->arch.local_int.pending_irqs)
+ /* __vcpu_run() will exit after delivering the interrupt. */
+ return false;
+ return true;
+}
+
 int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
 {
  int rc, per_rc = 0;
@@ -645,9 +658,7 @@ int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
  return -EOPNOTSUPP;
  }
 
- /* process PER, also if the instruction is processed in user space */
- if (vcpu->arch.sie_block->icptstatus & 0x02 &&
- (!rc || rc == -EOPNOTSUPP))
+ if (should_handle_per_ifetch(vcpu, rc))
  per_rc = kvm_s390_handle_per_ifetch_icpt(vcpu);
  return per_rc ? per_rc : rc;
 }