For KVM the code is run pretty much natively on the host CPU, so all
CPU extensions available on the host CPU can be also used inside the VM.
To expose that information to the VM we should pass "-cpu host", so the
VM is aware of which CPU is in use.
For CPU emulation, QEMU uses a rather minimal CPU on x86_64 by default.
It does not have support for SSE3/4 etc, which may be required for some
applications to work properly (e.g. Android in Anbox). Add a --cpu flag
to make the emulated CPU configurable. Useful values are for example
--cpu max to emulate all implemented CPU features.
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