About the SENDUIPI instruction: https://www.felixcloutier.com/x86/senduipi https://www.felixcloutier.com/x86/senduipi It seems to require the kernel to set the

About the SENDUIPI instruction: https://www.felixcloutier.com/x86/senduipi https://www.felixcloutier.com/x86/senduipi It seems to require the kernel to set the IA32_UINTR_TT MSR before it does anything, so at least you can't send random IPIs to other processes from userspace. I wonder about the cost of supporting these unused features in Intel chips. Will Intel keep including it forever even if no one adopts it? Drop it? (It is controlled by a CPUID feature flag so that is possible.)