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> One advantage very specific to the low-level way ESXi works, because there's no underlying operating system to get in the way, is the ability to 'pass through' real hardware to the virtual machine — say a specific network card, or a USB hub. Or most importantly for macOS: a GPU.

This is not at all specific to ESXi... you can do PCIe and USB passthrough with qemu running on Linux. The operating system doesn't get in the way.

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Quibbling a bit with the details here.

> This is not at all specific to ESXi... you can do PCIe and USB passthrough with qemu running on Linux.

This is true.

> The operating system doesn't get in the way.

This isn't, really, at least not qemu does quite a bit of fiddling under the hoot -- without VFIO or legacy KVM pass-through, the operating system very much gets in the way. Linux now provides facilities that allow qemu to pass through devices -- that is, it provides the APIs necessary to move it back out of the way.

I don't know to what extent ESXi looks like pure-kernel setup of passthrough vruss KVM_ASSIGN_DEVICE versus VFIO -- that would be quite interesting.

GPU passthrough specifically is tricky - I know ESXi does it well but you of course have to dedicate a physical GPU to a single VM. No sharing.

I know they were working on it with Hyper-V awhile back but who knows howe well it works

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