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As a result, on > hardware supporting these leaves, we read the real hardware values into the > raw policy, then copy into host, and all the way into the PV/HVM default > policies. > > All 4 of these leaves have enable bits (first two by TopoExt, next by SEV, > next by PQOS), so any software following the rules is fine and will leave them > alone. However, leaf 0x8000001d takes a subleaf input and at least two > userspace utilities have been observed to loop indefinitely under Xen (clearly > waiting for eax to report "no more cache levels"). > > Such userspace is buggy, but Xen's behaviour isn't great either. Just another remark, since I stumbled across this again while preparing the backports: I'm not convinced such user space is to be called buggy. Generic CPUID dumping tools won't normally look for particular features. Their knowledge is usually limited to knowing where sub-leaves exist and how to determine how many of them there are. Anything beyond that would make a supposedly simple tool complicated. Jan