KVM: mmu_notifier: Flush TLBs before releasing mmu_lock

(cherry picked from commit 565f3be2

Other threads may process the same page in that small window and skip
TLB flush and then return before these functions do flush.
Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

virt/kvm/kvm_main.c

@@ -289,15 +289,15 @@ static void kvm_mmu_notifier_invalidate_page(struct mmu_notifier *mn,
 	 */
 	idx = srcu_read_lock(&kvm->srcu);
 	spin_lock(&kvm->mmu_lock);
+
 	kvm->mmu_notifier_seq++;
 	need_tlb_flush = kvm_unmap_hva(kvm, address) | kvm->tlbs_dirty;
-	spin_unlock(&kvm->mmu_lock);
-	srcu_read_unlock(&kvm->srcu, idx);
-
 	/* we've to flush the tlb before the pages can be freed */
 	if (need_tlb_flush)
 		kvm_flush_remote_tlbs(kvm);
 
+	spin_unlock(&kvm->mmu_lock);
+	srcu_read_unlock(&kvm->srcu, idx);
 }
 
 static void kvm_mmu_notifier_change_pte(struct mmu_notifier *mn,
@@ -335,12 +335,12 @@ static void kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 	for (; start < end; start += PAGE_SIZE)
 		need_tlb_flush |= kvm_unmap_hva(kvm, start);
 	need_tlb_flush |= kvm->tlbs_dirty;
-	spin_unlock(&kvm->mmu_lock);
-	srcu_read_unlock(&kvm->srcu, idx);
-
 	/* we've to flush the tlb before the pages can be freed */
 	if (need_tlb_flush)
 		kvm_flush_remote_tlbs(kvm);
+
+	spin_unlock(&kvm->mmu_lock);
+	srcu_read_unlock(&kvm->srcu, idx);
 }
 
 static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn,
@@ -378,13 +378,14 @@ static int kvm_mmu_notifier_clear_flush_young(struct mmu_notifier *mn,
 
 	idx = srcu_read_lock(&kvm->srcu);
 	spin_lock(&kvm->mmu_lock);
-	young = kvm_age_hva(kvm, address);
-	spin_unlock(&kvm->mmu_lock);
-	srcu_read_unlock(&kvm->srcu, idx);
 
+	young = kvm_age_hva(kvm, address);
 	if (young)
 		kvm_flush_remote_tlbs(kvm);
 
+	spin_unlock(&kvm->mmu_lock);
+	srcu_read_unlock(&kvm->srcu, idx);
+
 	return young;
 }