[v1] KVM: kvm_io_bus_unregister_dev() should never fail

Commit Message

David Hildenbrand March 23, 2017, 4:20 p.m. UTC

> As this may set kvm->buses[bus_idx] to NULL, don't you also need to
> guard for bus == NULL in kvm_io_bus_destroy()? (I looked at the code on
> kvm/queue.)

very right, so something like this?


Thanks!

> 
>>  	synchronize_srcu_expedited(&kvm->srcu);
>>  	kfree(bus);
>> -	return r;
>> +	return;
>>  }
>

Comments

Cornelia Huck March 23, 2017, 4:40 p.m. UTC | #1

On Thu, 23 Mar 2017 17:20:48 +0100
David Hildenbrand <[e-mail]> wrote:

> 
> > As this may set kvm->buses[bus_idx] to NULL, don't you also need to
> > guard for bus == NULL in kvm_io_bus_destroy()? (I looked at the code on
> > kvm/queue.)
> 
> very right, so something like this?
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e1be4b4..ef1aa7f 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -728,7 +728,8 @@ static void kvm_destroy_vm(struct kvm *kvm)
>         spin_unlock(&kvm_lock);
>         kvm_free_irq_routing(kvm);
>         for (i = 0; i < KVM_NR_BUSES; i++) {
> -               kvm_io_bus_destroy(kvm->buses[i]);
> +               if (kvm->buses[i])
> +                       kvm_io_bus_destroy(kvm->buses[i]);
>                 kvm->buses[i] = NULL;
>         }
>         kvm_coalesced_mmio_free(kvm);
> 
> Thanks!
> 
> > 
> >>  	synchronize_srcu_expedited(&kvm->srcu);
> >>  	kfree(bus);
> >> -	return r;
> >> +	return;
> >>  }
> > 
> 
> 

Either that, or an early exit for bus == NULL in kvm_io_bus_destroy().
(I think the second option is more straightforward.)

David Hildenbrand March 23, 2017, 5:15 p.m. UTC | #2

> 
> Either that, or an early exit for bus == NULL in kvm_io_bus_destroy().
> (I think the second option is more straightforward.)

I prefer to have the checks where kvm->buses[x] is actually accessed. So
the chance of missing yet another check is easier to verify.

Will send out v2 in a couple of minutes. Thanks!

Patch

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e1be4b4..ef1aa7f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -728,7 +728,8 @@  static void kvm_destroy_vm(struct kvm *kvm)
        spin_unlock(&kvm_lock);
        kvm_free_irq_routing(kvm);
        for (i = 0; i < KVM_NR_BUSES; i++) {
-               kvm_io_bus_destroy(kvm->buses[i]);
+               if (kvm->buses[i])
+                       kvm_io_bus_destroy(kvm->buses[i]);
                kvm->buses[i] = NULL;
        }
        kvm_coalesced_mmio_free(kvm);