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

Jason Wang
2021-06-03T02:32:55Z

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);
>>