Intel Skylake/Kaby Lake processors: broken hyper-threading

https://www.intel.com/content/dam/www/public/us/en/docume... lists 173 issues in Haswell alone. Of things that can be hit by an unprivileged user:

HSD45. Certain Combinations of AVX Instructions May Cause Unpredictable System Behavior (sounds familiar?)
HSD136. Software Using Intel(R) TSX May Result In Unpredictable System Behavior (widely published, eventually was so bad that Intel had to rip out TSX from all of Haswell)
HSD142. Interactions Between Multiple Unaligned Memory Accesses And Locked Instructions May Lead to a Machine Check (try to write lock-free code? expect a crash)
HSD145. Operand-Size Override Prefix Causes 64-bit Operand Form of MOVBE Instruction to Cause a #UD (try to load big-endian data? expect a crash)
HSD162. MOVNTDQA From WC Memory May Pass Earlier Locked Instructions (try to use non-temporal loads from GPU memory? your serialization guarantees are off)

This isn't unique to Intel. See e.g. the case a while back where Ryzen would overheat and die if you ran a bunch of AVX muladds in parallel without ever touching memory.