Right, so a VT-x takes time - if we're talking 2500 cycles per
roundtrip, then you get approx one million of them per second - fair

 Not much time left for anything else though at that exit rate :(

As you point out the VM is launched absolutely bare.

So then, strategies would need to be devised for how to run the code.

I guess this would range all the way from running a barebones memory
management and pthreads implemenation (both those exist at least for
amd64, if I got it right, not sure how up to date they are though),

..to running a minimal BSD/Linux kernel within the VM for maxing

Perhaps some neat memory dumping drick could be applied to zero the
BSD/Linux kernel boot time, i.e. the kernel doesn't boot but it's just
loaded from a hibernated memory image.

 Yep, that's possible.

Okay, so, there are two aspects to this problem now:

  (1) The BHyVe specific parts, about how to use BHyVe's interfaces to
deliver the virtualization/sandbox aspect, and

  (2) The guest specific parts, as in how run the intended
libraries/binaries as close to the metal as possible and with as low RAM
overhead as possible (and CPU overhead) within the sandbox.

I guess (2) is off-topic to this mailing list so should be looked into

If you have any spontaneous thoughts on that one though, of course feel
free to share them :)

There are many examples of small embedded o/s's that could easily be run in this environment - a reasonable example is the FreeBSD loader itself.

And, (1) is on this ML's topic, so I can direct any subsequent questions
about that to here.

If you have any particular references with regard to header files, man
page or example program source files, feel free to pass them!

 Not a lot of documentation other than the bhyve source code itself.

lib/libvmmapi/vmmapi_freebsd.c is an example of how to set up a 64-bit environment that the FreeBSD/amd64 kernel can be directly executed from.

https://github.com/grehan-freebsd/grub2-bhyve/blob/master/grub-core/kern/emu/bhyve_hostif.c sets up a flat 32-bit environment that Linux/OpenBSD/NetBSD kernels expect to be invoked in.

usr.sbin/bhyve/bhyverun.c has the main run loop for bhyve, which demonstrates how exits are handled.



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