Messages in this thread | | | Date | Thu, 18 Aug 2022 10:34:36 -0700 | Subject | Re: [PATCH 3/5] x86/microcode/intel: Allow a late-load only if a min rev is specified | From | Dave Hansen <> |
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On 8/15/22 00:46, Peter Zijlstra wrote: > What if any validation do you have to ensure min_rev does as promised? > That is, ucode can very easily lie about the number and still remove an > MSR or CPUID enumerated feature.
We can absolutely add sanity checks to this. It would not be hard at all to, for instance, dump out all the CPUID leaves we can get our hands on and diff them before and after a ucode update.
That said, min_rev is *architectural*. It includes an architectural promise from Intel that the ucode won't lie. If Intel is breaking architectural promises, it has bigger problems on its hands.
Bugs happen, of course -- even bugs in architectural features. If there are enough bugs that we can't trust min_rev, late-loading will just get disabled again, probably permanently. Our Intel colleagues should have all the incentive in the world to be very, very careful with min_rev.
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