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

在 2021/6/3 上午9:48, Andi Kleen 写道:

quoted

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

quoted

Thanks

quoted

              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);

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