One of the many features merged for the 5.7 kernel is split-lock detection for the x86 architecture.
This feature has encountered a fair amount of
controversy over the course of its development, with the result that
the time between its initial posting and appearance in a released kernel
will end up being over two years. As it happens, there is another hurdle
for split-lock detection even after its merging into the mainline; this
feature threatens to create problems for a number of virtualization
solutions, and it’s not clear what the solution would be.

Source: LWN.net – [$] VMX virtualization runs afoul of split-lock detection