Even modern Intel CPUs are losing up to 36% performance with the new Spectre BHI patch

Spectre

VUSec - the systems and network security group at the Vrije Universiteit (VU) Amsterdam research institute - disclosed details about a new vulnerability based on the infamous Spectre v2 that affects both Intel and Arm CPUs. AMD CPUs, however, are unaffected.

The Spectre vulnerability in general exploits CPUs that use branch prediction or speculation, and VUSec notes that this new threat can even circumvent Enhanced Indirect Branch Restricted Speculation (EIBRS) hardware mitigations (or CSV2 in the case of ARM) by using branch history buffer (BHB). Hence, the new variant is called Spectre-BHB or Branch History Injection (BHI).

Consequently, Linux security patches for x86 processors were also released on the same day and added to the Linux 5.17 mainline kernel. As such, Phoronix decided to test the patch on a couple of Intel processors to see the performance impact that it can have.

First, we have the latest 12th Gen Alder Lake-S Core i9-12900K and the processor loses up to 26.7% performance when measuring the Sockperf throughput. Other than this, the i9-12900K loses anywhere between 2 to 14.5% with the Spectre-BHB patch.

Performance loss after Spectre-BHB patch

An 11th Gen Tiger Lake Core i7-1185G7 processor was also tested and this time the maximum loss is even greater as an unpatched system performed up to 35.6% better. In another test, the unpatched system was 34.1% faster. Overall, other than these two tests, the unpatched system lost anywhere between 2% to 26.1% performance.

Performance loss after Spectre-BHB patch

Interestingly, as you can see in the case of the Selenium benchmark, the i7-1185G7 actually gained a little performance (2.2%) on the patched machine.

You can read about the full test setup and such in the original Phoronix article linked at the source below.

Source and images: Phoronix

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