On 08/05/2013 12:26 PM, Michael S. Tsirkin wrote:
This is a PV technology which to me looks like it was rushed through and not only set on by default, but without a way to disable it - apparently on the assumption there's 0 chance it can cause any damage. Now that we do know the chance it's not there, why not go back to the standard interface, and why not give users a chance to enable/disable it?
In other words, let's do the standard thing, and make the new device available with -device pvpanic. And in BIOS, let's just obey what QEMU tells us to do, and not create the device if it's not there.
Libvirt has no problem enabling -device pvpanic for all guests where <on_crash> is set to a non-default value, since the use of <on_crash> is a sufficient hint that the user expects the guest to be able to notify of a crash in the first place. But I definitely agree that it is more conservative to ask libvirt to always provide -device pvpanic than it is to blindly enable the device and hope that it never causes damage.