On Fri, 17 Apr 2015 15:59:15 +0800 Fam Zheng <f...@redhat.com> wrote:
> Currently, virtio code chooses to kill QEMU if the guest passes any invalid > data with vring. That has drawbacks such as losing unsaved data (e.g. when > guest user is writing a very long email), or possible denial of service in > a nested vm use case where virtio device is passed through. > > virtio-1 has introduced a new status bit "NEEDS RESET" which could be used to > improve this by communicating the error state between virtio devices and > drivers. The device notifies guest upon setting the bit, then the guest driver > should detect this bit and report to userspace, or recover the device by > resetting it. > > This series makes necessary changes in virtio core code, based on which > virtio-blk is converted. Other devices now keep the existing behavior by > passing in "error_abort". They will be converted in following series. The > Linux > driver part will also be worked on. > > One concern with this behavior change is that it's now harder to notice the > actual driver bug that caused the error, as the guest continues to run. To > address that, we could probably add a new error action option to virtio > devices, similar to the "read/write werror" in block layer, so the vm could > be > paused and the management will get an event in QMP like pvpanic. This work > can > be done on top. In principle, this looks nice; I'm not sure however how this affects non-virtio-1 devices. If a device is operating in virtio-1 mode, everything is clearly specified: The guest is notified and if it is aware of the NEEDS_RESET bit, it can react accordingly. But what about legacy devices? Even if they are notified, they don't know to check for NEEDS_RESET - and I'm not sure if the undefined behaviour after NEEDS_RESET might lead to bigger trouble than killing off the guest.