> I just want to point out that you are free to use your own, more complete or faster instruction emulator with WHP. True. This is an unimportant rant on my si

> I just want to point out that you are free to use your own, more complete or faster instruction emulator with WHP. True. This is an unimportant rant on my side, since it would be nice to have a complete emulator out-of-the-box. But it's true it can be solved in userspace (EDIT: now I wonder how could we inject exceptions back into the guest, should they occur during emulation in userspace). > I'm curious what you mean about no guest debugging support. This would allow the host to introduce software/hardware breakpoints and single-stepping through the guest. This is extremely relevant to debug bootloaders/microkernels, or in my case, closed-source kernels that do not support debugging. Some hypervisors, e.g. KVM (and soon HAXM), support this: check "KVM_DEBUG_GUEST" at https://www.kernel.org/doc/Documentation/virtual/kvm/api.txt https://www.kernel.org/doc/Documentation/virtual/kvm/api.txt > Also curious about the other shortcomings so that we can prioritize appropriately. The API provides no way to add/override/hook arbitrary MSRs while handling guests's rdmsr/wrmsr instructions, or override CPUID leaves/subleaves. This is required to run certain kernels are designed to run in specific x86 processors. Of course, most hypervisors lack this feature and I understand that WHPX is fairly recent so I'm not complaining about the lack of it. My issue is rather that closed-source implementations are not helpful for researchers since shortcomings like these means the whole library is no longer usable for us. Comparatively adding such features to (say) KVM or HAXM takes just few hours. Also, don't get me wrong. I feel it's incredibly valuable having finally an API allowing developers benefit from Hyper-V in userland. I'm just concerned about the current trend of hypervisor APIs, as every vendor eventually just ships a closed hypervisor library for its own platform, and developers have to put up with 5 different ways of doing the same thing. (PS: I've invested quite some time on HAXM, but I'm not affiliated with Intel in any way)