On 06/07/15 18:08, Lengyel, Tamas wrote:

Having said that (and with the understading that it is beyond the scope
of this patch), a way to validate things like these is a good idea. I
wonder if, in a future patch, we could not have ./configure detect these
things and simply disable the relevant VM_EVENT_FLAG constants with
#if(n)defs, for example. That way, you wouldn't be able to compile code
that wouldn't work silently on platforms where that is the case.

It would be something worth investigating, definitely.

It would be mad to conditionally compile out code based on the features or lackthereof of the build machine.

For bits like this, there must be active negotiation between userspace and the running hypervisor to see what it can support.  Imagine if the user disabled the monitor trap feature in the BIOS?  Userspace cannot possibly assume that because it is running on Intel, that the feature is present and usable.