vmm: Use struct vcpu in the instruction emulation code.

[jhb]

Summary

This passes struct vcpu down in place of struct vm and and integer
vcpu index through the in-kernel instruction emulation code. To
minimize userland disruption, helper macros are used for the vCPU
arguments passed into and through the shared instruction emulation
code.

A few other APIs used by the instruction emulation code have also been
updated to accept struct vcpu in the kernel including
vm_get/set_register and vm_inject_fault.

[corvink]

sys/amd64/include/vmm_instruction_emul.h

36–44

I have a bad feeling about this "hack". I think it will be hard to maintain.

[jhb]

sys/amd64/include/vmm_instruction_emul.h

36–44

There are some other options. illumos uses separate instruction emulation code in userland rather than sharing the code. Another option is to add a 'struct vcpu' to libvmmapi.h. I started on this latter approach but it would be another large change in its own right. That said, having a 'struct vcpu' and using it in bhyve in userspace might be a nice cleanup. It also makes it easier to possibly use anonymous file descriptors for vCPUs (something @grehan has talked about in the past).

[corvink]

sys/amd64/include/vmm_instruction_emul.h

36–44

A 'struct vcpu' in userspace sounds good. If we have to add more of such "hacks" in the future, we should consider using another approach for instruction emulation.

I know it requires some work to get rid of this "hack". So, this commit is fine for now.

[markj]

sys/amd64/include/vmm_instruction_emul.h

36–44

I'd suggest adding a comment noting that we should eventually modify userspace to use the same interface as the kernel.

[jhb]

Expand comment for VCPU* helper macros