On Tue, Apr 21, 2015 at 01:50:33PM +0800, Fam Zheng wrote: > On Tue, 04/21 07:22, Michael S. Tsirkin wrote: > > On Tue, Apr 21, 2015 at 10:37:00AM +0800, Fam Zheng wrote: > > > On Mon, 04/20 19:36, Michael S. Tsirkin wrote: > > > > On Fri, Apr 17, 2015 at 03:59:15PM +0800, Fam Zheng 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. > > > > > > > > Unfortunately, virtio 1 spec does not have a conformance statement > > > > that requires driver to recover. We merely have a non-normative looking > > > > text: > > > > Note: For example, the driver can’t assume requests in flight > > > > will be completed if DEVICE_NEEDS_RESET is set, nor can it assume that > > > > they have not been completed. A good implementation will try to recover > > > > by issuing a reset. > > > > > > > > Implementing this reset for all devices in a race-free manner might also > > > > be far from trivial. I think we'd need a feature bit for this. > > > > OTOH as long as we make this a new feature, would an ability to > > > > reset a single VQ be a better match for what you are trying to > > > > achieve? > > > > > > I think that is too complicated as a recovery measure, a device level resetting > > > will be better to get to a deterministic state, at least. > > > > Question would be, how hard is it to stop host from using all queues, > > retrieve all host OS state and re-program it into the device. > > If we need to shadow all OS state within the driver, then that's a lot > > of not well tested code with a possibility of introducing more bugs. > > I don't understand the question. In this series the virtio-blk device will not > pop any more requests, and as long as the reset is properly handled, both guest > and host should go back to a good state. > > > > > > > > > > > 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. > > > > > > > > At the architectural level, that's only one concern. Others would be > > > > - workloads such as openstack handle guest crash better than > > > > a guest that's e.g. slow because of a memory leak > > > > > > What memory leak are you referring to? > > > > That was just an example. If host detects a malformed ring, it will > > crash. But often it doesn't, result is buffers not being used, so guest > > can't free them up. > > > > > > - it's easier for guests to probe host for security issues > > > > if guest isn't killed > > > > - guest can flood host log with guest-triggered errors > > > > > > We can still abort() if guest is triggering error too quickly. > > > > > > Absolutely, and if it looked like I'm against error detection and > > recovery, this was not my intent. > > > > I am merely saying we can't apply this patchset as is, deferring > > addressing the issues to patches on top. > > > > But I have an idea: refactor the code to use error_abort. > > That is patch 1-9 of this series. Or do you mean also refactor and pass > error_abort to the memory core? > > Fam So if you like just patches 1-9 applied, this sounds reasonable. I'll provide review comments on the individual patches. > >This way we > > can apply the patchset without making functional changes, and you can > > make progress to complete this, on top. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
