KVM: Make kvm_mmu_change_mmu_pages() take mmu_lock by itself

No reason to make callers take mmu_lock since we do not need to protect
kvm_mmu_change_mmu_pages() and kvm_mmu_slot_remove_write_access()
together by mmu_lock in kvm_arch_commit_memory_region(): the former
calls kvm_mmu_commit_zap_page() and flushes TLBs by itself.

Note: we do not need to protect kvm->arch.n_requested_mmu_pages by
mmu_lock as can be seen from the fact that it is read locklessly.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

arch/x86/kvm/mmu.c

@@ -2143,6 +2143,8 @@ void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int goal_nr_mmu_pages)
 	 * change the value
 	 */
 
+	spin_lock(&kvm->mmu_lock);
+
 	if (kvm->arch.n_used_mmu_pages > goal_nr_mmu_pages) {
 		while (kvm->arch.n_used_mmu_pages > goal_nr_mmu_pages &&
 			!list_empty(&kvm->arch.active_mmu_pages)) {
@@ -2157,6 +2159,8 @@ void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int goal_nr_mmu_pages)
 	}
 
 	kvm->arch.n_max_mmu_pages = goal_nr_mmu_pages;
+
+	spin_unlock(&kvm->mmu_lock);
 }
 
 int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn)

arch/x86/kvm/x86.c

@@ -3270,12 +3270,10 @@ static int kvm_vm_ioctl_set_nr_mmu_pages(struct kvm *kvm,
 		return -EINVAL;
 
 	mutex_lock(&kvm->slots_lock);
-	spin_lock(&kvm->mmu_lock);
 
 	kvm_mmu_change_mmu_pages(kvm, kvm_nr_mmu_pages);
 	kvm->arch.n_requested_mmu_pages = kvm_nr_mmu_pages;
 
-	spin_unlock(&kvm->mmu_lock);
 	mutex_unlock(&kvm->slots_lock);
 	return 0;
 }
@@ -6894,7 +6892,6 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	if (!kvm->arch.n_requested_mmu_pages)
 		nr_mmu_pages = kvm_mmu_calculate_mmu_pages(kvm);
 
-	spin_lock(&kvm->mmu_lock);
 	if (nr_mmu_pages)
 		kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
 	/*
@@ -6902,9 +6899,11 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	 * Existing largepage mappings are destroyed here and new ones will
 	 * not be created until the end of the logging.
 	 */
-	if (npages && (mem->flags & KVM_MEM_LOG_DIRTY_PAGES))
+	if (npages && (mem->flags & KVM_MEM_LOG_DIRTY_PAGES)) {
+		spin_lock(&kvm->mmu_lock);
 		kvm_mmu_slot_remove_write_access(kvm, mem->slot);
-	spin_unlock(&kvm->mmu_lock);
+		spin_unlock(&kvm->mmu_lock);
+	}
 	/*
 	 * If memory slot is created, or moved, we need to clear all
 	 * mmio sptes.