With AMD Zen 4, It's Surprisingly Not Worthwhile Disabling CPU Security Mitigations

[phoronix]

Phoronix: With AMD Zen 4, It's Surprisingly Not Worthwhile Disabling CPU Security Mitigations

While some Linux enthusiasts eagerly recommend users boot their systems with the "mitigations=off" kernel parameter for run-time disabling of various relevant CPU security mitigations for Spectre, Meltdown, L1TF, TAA, Retbleed, and friends, with the new AMD Ryzen 7000 "Zen 4" processors while still needing some software mitigations, it's surprisingly faster for the most part leaving the relevant mitigations enabled...

https://www.phoronix.com/news/AMD-Zen-4-Mitigations-Off

[skeevy420]

Wow! I feel like that's the first real reason I've seen that's actually compelling me to want to upgrade my Zen 2 system outside of Newer, Better, and Faster. At the same time these results make me curious how fast Zen 4 and the Intel equivalents would be if there weren't hardware and firmware mitigations in place.

I've done enough grammar edits today that this article is triggering me. That last sentence starts with But and also uses but to make it a compound sentence.

[rhysperry111]

I'm curious how something like this could even happen

[stormcrow]

I'm curious how something like this could even happen

They likely 'just' optimized for the concepts behind the mitigations same as processor designers have been doing for certain language concepts and usage trends.

The devil is in the details and that 'just' covers a multitude of design decisions and trade offs like with any other design considerations. Time will tell if the changes are brittle or resilient, but the one thing I'm sure of is that even at this point we've not seen the last of these types of exploits.

[sdack]

This is witchcraft!1!

[andrebrait]

I'm gonna wait until I hear from someone at AMD about this. It looks weird.

[mahurinj]

Wasn't one of the benefits of Zen 4 that some/most of these vulnerabilities were addressed at the hardware level?

[kozman]

That's the most counter-intuitive thing I've ever seen. All other benchmarks of the past showed that mitigations=off much improved perf at the expense of security. So does this imply AMD designed Zen 4 with the assumption of mitigation=on as a means of protecting users from themselves and disabling will cost you perf if you do? Carrot + stick?

[kozman]

I'm gonna wait until I hear from someone at AMD about this. It looks weird.

Yeah, something seems odd with it.

[milkylainen]

Nope. Not believing that more code and worse code is going to do better than them removed.
Something is fishy here.