It's really as simple as just going into the motherboard configuration + raising Turbo multipliers + raising core multipliers, keeping on eye on the voltage and using mprime (aka Prime95 for Windows users) to stress test with AVX2 to make sure it doesn't get too hot under load.
It fundamentally needs to be possible, because an OS that doesn't support it (at context switch) has to be able to prevent userspace from using it.
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It needs to be able to communicate that it's unavailable so that userspace doesn't try to use it. It's good if it's possible to make it trap instead of doing anything (needed for this use case to be sane) but it's communicating it that matters for making userspace not break.
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Both are needed. If you can't make it trap, processes that shouldn't be able to communicate can use it as malicious covert channel.
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now that I look at it, clearcpuid only seems to affect /proc/cpuinfo, cpuid(1) still shows AVX as enabled... weird.
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Maybe noxsave works properly since it seems like it must for the reason
@RichFelker pointed out. -
I've rebooted with noxsave and AVX is still present in cpuid outputs (and I confirmed that the kernel uses fxsave via dmesg). weird.
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It traps if it's actually used though, right?
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ah yes, I figured it out. kernel never does cpuid emulation, only kvm can do that. and xsave has a bit in CR4.
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