* Jason Wang <jasow...@redhat.com> [2024-07-26 10:47:59]: > > 2) For PCI pass-through devices, we are concerned of letting VMM be in > > charge of > > emulating the complete configuration space (how can VM defend against > > invalid > > attributes presented for passthr devices)? > > Virtio driver has been hardened for this, for example: > > commit 72b5e8958738aaa453db5149e6ca3bcf416023b9 > Author: Jason Wang <jasow...@redhat.com> > Date: Fri Jun 4 13:53:50 2021 +0800 > > virtio-ring: store DMA metadata in desc_extra for split virtqueue > > More hardening work is ongoing.
I think above change is not sufficient for what we are looking for. In particular for pass-through PCI devices, we are concerned that a untrusted (compromised?) VMM can return invalid attributes when the confidential VM reads the configuration space. These are PCI devices that may not support TDISP. Hypervisor, being a trusted entity and controlling the PCI bus emulation can ensure that the confidential VM sees valid attributes for all devices (physical and virtual) that are enumerated on the bus. That's a key reason why we want hypervisor to emulate access to configuration space of all PCI devices enumerated by VM. That I think necessitates that hypervisor handle access to virtio device configuration space as well (even if MSI-X obviates the performance arguments of hypervisor doing so)! Thanks vatsa
