Re: [PATCH v1 1/8] virtio: Force only split mode with protected guest

[Jason Wang]

在 2021/6/3 上午9:48, Andi Kleen 写道:
> > So we will see huge performance regression without indirect 
> > descriptor. We need to consider to address this.
>
> A regression would be when some existing case would be slower.
>
> That's not the case because the behavior for the existing cases does 
> not change.
>
> Anyways when there are performance problems they can be addressed, but 
> first is to make it secure.


I agree, but I want to know why indirect descriptor needs to be 
disabled. The table can't be wrote by the device since it's not coherent 
swiotlb mapping.

Thanks


> -Andi
>
>
> > Thanks
> >
> >
> > >               break;
> > >           case VIRTIO_RING_F_EVENT_IDX:
> > >               break;
> > > @@ -2231,9 +2240,12 @@ void vring_transport_features(struct 
> > > virtio_device *vdev)
> > >           case VIRTIO_F_ACCESS_PLATFORM:
> > >               break;
> > >           case VIRTIO_F_RING_PACKED:
> > > +            if (protected_guest_has(VM_MEM_ENCRYPT))
> > > +                goto clear;
> > >               break;
> > >           case VIRTIO_F_ORDER_PLATFORM:
> > >               break;
> > > +        clear:
> > >           default:
> > >               /* We don't understand this bit. */
> > >               __virtio_clear_bit(vdev, i);