KVM: x86: Fix memory leak in vmx.c

If userspace creates and destroys multiple VMs within the same process
we leak 20k of memory in the userspace process context per VM.  This
patch frees the memory in kvm_arch_destroy_vm.  If the process exits
without closing the VM file descriptor or the file descriptor has been
shared with another process then we don't free the memory.

It's still possible for a user space process to leak memory if the last
process to close the fd for the VM is not the process that created it.
However, this is an unexpected case that's only caused by a user space
process that's misbehaving.
Signed-off-by: NAndrew Honig <ahonig@google.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

arch/x86/kvm/x86.c

@@ -6859,6 +6859,23 @@ void kvm_arch_sync_events(struct kvm *kvm)
 
 void kvm_arch_destroy_vm(struct kvm *kvm)
 {
+	if (current->mm == kvm->mm) {
+		/*
+		 * Free memory regions allocated on behalf of userspace,
+		 * unless the the memory map has changed due to process exit
+		 * or fd copying.
+		 */
+		struct kvm_userspace_memory_region mem;
+		memset(&mem, 0, sizeof(mem));
+		mem.slot = APIC_ACCESS_PAGE_PRIVATE_MEMSLOT;
+		kvm_set_memory_region(kvm, &mem);
+
+		mem.slot = IDENTITY_PAGETABLE_PRIVATE_MEMSLOT;
+		kvm_set_memory_region(kvm, &mem);
+
+		mem.slot = TSS_PRIVATE_MEMSLOT;
+		kvm_set_memory_region(kvm, &mem);
+	}
 	kvm_iommu_unmap_guest(kvm);
 	kfree(kvm->arch.vpic);
 	kfree(kvm->arch.vioapic);