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

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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);



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