cpuid_pass2 can clobber leaf 7
When we started adding support for CPUID features in leaf 7, we neglected to notice a part of what happens in cpuid_pass2. Importantly, it will re-enumerate all of the standard leaves. Leaf 7 is different from other cpuid leaves, in that it uses %eax to index into it, but then also uses %ecx to suggest a sub leaf to look at.
However, with certain newer systems, we actually have a value in %ecx being enumerated. This means that when we come back around to re-enumerate it in cpuid_pass2, we end up referring to an invalid leaf, which causes us to end up zeroing the entire set. This causes us to end up removing all the features on this leaf.