KVM: MMU: move mmu pages calculated out of mmu lock

kvm_mmu_calculate_mmu_pages need to walk all memslots and it's protected by
kvm->slots_lock, so move it out of mmu spinlock
Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/x86.c

@@ -6105,7 +6105,7 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 				int user_alloc)
 {
 
-	int npages = mem->memory_size >> PAGE_SHIFT;
+	int nr_mmu_pages = 0, npages = mem->memory_size >> PAGE_SHIFT;
 
 	if (!user_alloc && !old.user_alloc && old.rmap && !npages) {
 		int ret;
@@ -6120,12 +6120,12 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 			       "failed to munmap memory\n");
 	}
 
+	if (!kvm->arch.n_requested_mmu_pages)
+		nr_mmu_pages = kvm_mmu_calculate_mmu_pages(kvm);
+
 	spin_lock(&kvm->mmu_lock);
-	if (!kvm->arch.n_requested_mmu_pages) {
-		unsigned int nr_mmu_pages = kvm_mmu_calculate_mmu_pages(kvm);
+	if (nr_mmu_pages)
 		kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
-	}
-
 	kvm_mmu_slot_remove_write_access(kvm, mem->slot);
 	spin_unlock(&kvm->mmu_lock);
 }