[PATCH 3/4] KVM: Refactor mark_page_dirty_in_slot()

[Gavin Shan <gshan@redhat.com>]

Refactor mark_page_dirty_in_slot() to bail early if the memory slot
isn't existing or dirty page tracking is disabled on it. It's the
preparatory work for the forth coming fixes.

No functional change intended.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 virt/kvm/kvm_main.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 9c60384b5ae0..90f538433916 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3317,6 +3317,8 @@ void mark_page_dirty_in_slot(struct kvm *kvm,
 		 	     gfn_t gfn)
 {
 	struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
+	unsigned long rel_gfn;
+	u32 slot;
 
 #ifdef CONFIG_HAVE_KVM_DIRTY_RING
 	if (WARN_ON_ONCE(vcpu && vcpu->kvm != kvm))
@@ -3325,15 +3327,16 @@ void mark_page_dirty_in_slot(struct kvm *kvm,
 	WARN_ON_ONCE(!vcpu && !kvm_arch_allow_write_without_running_vcpu(kvm));
 #endif
 
-	if (memslot && kvm_slot_dirty_track_enabled(memslot)) {
-		unsigned long rel_gfn = gfn - memslot->base_gfn;
-		u32 slot = (memslot->as_id << 16) | memslot->id;
+	if (!memslot || !kvm_slot_dirty_track_enabled(memslot))
+		return;
 
-		if (kvm->dirty_ring_size && vcpu)
-			kvm_dirty_ring_push(vcpu, slot, rel_gfn);
-		else if (memslot->dirty_bitmap)
-			set_bit_le(rel_gfn, memslot->dirty_bitmap);
-	}
+	rel_gfn = gfn - memslot->base_gfn;
+	slot = (memslot->as_id << 16) | memslot->id;
+
+	if (kvm->dirty_ring_size && vcpu)
+		kvm_dirty_ring_push(vcpu, slot, rel_gfn);
+	else if (memslot->dirty_bitmap)
+		set_bit_le(rel_gfn, memslot->dirty_bitmap);
 }
 EXPORT_SYMBOL_GPL(mark_page_dirty_in_slot);
 
-- 
2.23.0