That those instructions had not been privileged has been widely considered as a serious design error of Intel 80286.
The virtualized modes introduced at about the same time by Intel and AMD, around 2005 / 2006, have been necessary mainly for fixing the broken privileged mode of x86/x86-64.
There is the well-known paper from IBM, published in 1970, "A Virtual Machine Time-Sharing System", which has listed the requirements for a CPU that can be virtualized, and which have been violated in the design of the Protected Mode of 80286 (in 1982), whose defects have been inherited by the later Intel and AMD CPUs.
In a CPU with a well-designed privileged mode there is no need for any other extra "hypervisor" mode, because an operating system cannot detect whether it is executed in the privileged mode on the real machine or in the non-privileged mode in a virtual machine, and the OS can be protected from the user processes by the same mechanisms that protect the user processes between themselves.
The UMIP feature available in all recent Intel and AMD CPUs is another fix for the original mistake.
The virtualized modes introduced at about the same time by Intel and AMD, around 2005 / 2006, have been necessary mainly for fixing the broken privileged mode of x86/x86-64.
There is the well-known paper from IBM, published in 1970, "A Virtual Machine Time-Sharing System", which has listed the requirements for a CPU that can be virtualized, and which have been violated in the design of the Protected Mode of 80286 (in 1982), whose defects have been inherited by the later Intel and AMD CPUs.
https://www.seltzer.com/margo/teaching/CS508.19/papers/meyer...
In a CPU with a well-designed privileged mode there is no need for any other extra "hypervisor" mode, because an operating system cannot detect whether it is executed in the privileged mode on the real machine or in the non-privileged mode in a virtual machine, and the OS can be protected from the user processes by the same mechanisms that protect the user processes between themselves.
The UMIP feature available in all recent Intel and AMD CPUs is another fix for the original mistake.