KVM: avoid warning on s390 in mark_page_dirty

Avoid warnings on s390 like
[ 1801.980931] CPU: 12 PID: 117600 Comm: kworker/12:0 Tainted: G            E     5.17.0-20220113.rc0.git0.32ce2abb03cf.300.fc35.s390x+next #1
[ 1801.980938] Workqueue: events irqfd_inject [kvm]
[...]
[ 1801.981057] Call Trace:
[ 1801.981060]  [<000003ff805f0f5c>] mark_page_dirty_in_slot+0xa4/0xb0 [kvm]
[ 1801.981083]  [<000003ff8060e9fe>] adapter_indicators_set+0xde/0x268 [kvm]
[ 1801.981104]  [<000003ff80613c24>] set_adapter_int+0x64/0xd8 [kvm]
[ 1801.981124]  [<000003ff805fb9aa>] kvm_set_irq+0xc2/0x130 [kvm]
[ 1801.981144]  [<000003ff805f8d86>] irqfd_inject+0x76/0xa0 [kvm]
[ 1801.981164]  [<0000000175e56906>] process_one_work+0x1fe/0x470
[ 1801.981173]  [<0000000175e570a4>] worker_thread+0x64/0x498
[ 1801.981176]  [<0000000175e5ef2c>] kthread+0x10c/0x110
[ 1801.981180]  [<0000000175de73c8>] __ret_from_fork+0x40/0x58
[ 1801.981185]  [<000000017698440a>] ret_from_fork+0xa/0x40

when writing to a guest from an irqfd worker as long as we do not have
the dirty ring.
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reluctantly-acked-by: David Woodhouse <dwmw@amazon.co.uk>
Message-Id: <20220113122924.740496-1-borntraeger@linux.ibm.com>
Fixes: 2efd61a6 ("KVM: Warn if mark_page_dirty() is called without an active vCPU")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/kvm_main.c

@@ -3163,8 +3163,10 @@ void mark_page_dirty_in_slot(struct kvm *kvm,
 {
 	struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
 
+#ifdef CONFIG_HAVE_KVM_DIRTY_RING
 	if (WARN_ON_ONCE(!vcpu) || WARN_ON_ONCE(vcpu->kvm != kvm))
 		return;
+#endif
 
 	if (memslot && kvm_slot_dirty_track_enabled(memslot)) {
 		unsigned long rel_gfn = gfn - memslot->base_gfn;