Intel’s latest chip have a nasty bug causes unpredictable system behavior

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Nasty bug

A flaw has been disclosed that impacts Intel 6th and 7th generation Skylake and Kaby Lake-based processors that support hyper-threading. Also, found on Intel related server processors, such as Xeon v5 and Xeon v6, and Intel Pentium processor models.

Henrique de Moraes Holschuh, a Debian Linux developer, revealed the Intel chip problem on the Debian developer list. Officially, Intel hasn’t acknowledged the problem, but engineers at Dell and Intel reveals the problem, and its fix, exists. Well, it’s not Linux-specific. Any operating system Windows, macOS, FreeBSD, can run into the problem.

Henrique says, affected users need to disable hyper-threading “immediately” in their BIOS or UEFI settings, because processors dangerously misbehave when hyper-threading is enabled. Symptoms include, application and system misbehavior, data corruption, and data loss.

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Intel’s errata

According to Intel’s errata, under complex micro-architectural conditions, short loops of less than 64 instructions that use AH, BH, CH or DH registers as well as their corresponding wider register may cause unpredictable system behavior. This can only happen when both logical processors on the same physical processor are active.

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The OCaml toolchain community first began investigating processors with these malfunctions back in January and found reports stemming back to at least the first half of 2016. The OCaml team was able to pinpoint the issue to Skylake’s hyper-threading implementation and notified Intel.

Intel and computer original equipment manufacturers (OEMS) are working on delivering a microcode update for these processors to fix this problem.

However, microcode fixes need to be implemented in BIOS/UEFI updates as well. It is not clear at this time if all major vendors have included these changes in their latest revisions though.

For Debian users:

  • Kaby Lake: Contact system vendors for BIOS/UEFI updates, meantime disables hyper-threading
  • Skylake: Depending on the model, an Intel-hyperthreading package is available, otherwise disable hyper-threading and wait for a BIOS/UEFI fix.

Other users will need platform-specific fixes for BIOS/UEFI upgrades to land from their system vendors.

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