KVM: Simplify kvm->tlbs_dirty handling

When this was introduced, kvm_flush_remote_tlbs() could be called
without holding mmu_lock.  It is now acknowledged that the function
must be called before releasing mmu_lock, and all callers have already
been changed to do so.

There is no need to use smp_mb() and cmpxchg() any more.

Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/linux/kvm_host.h

@@ -401,7 +401,9 @@ struct kvm {
 	unsigned long mmu_notifier_seq;
 	long mmu_notifier_count;
 #endif
-	long tlbs_dirty;
+	/* Protected by mmu_lock */
+	bool tlbs_dirty;
+
 	struct list_head devices;
 };