x86/retbleed: Add X86_FEATURE_CALL_DEPTH

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Intel SKL CPUs fall back to other predictors when the RSB underflows. The
only microcode mitigation is IBRS which is insanely expensive. It comes
with performance drops of up to 30% depending on the workload.

A way less expensive, but nevertheless horrible mitigation is to track the
call depth in software and overeagerly fill the RSB when returns underflow
the software counter.

Provide a configuration symbol and a CPU misfeature bit.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111147.056176424@infradead.org

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Thomas Gleixner 2022-09-15 13:11:19 +02:00 • committed by Peter Zijlstra

parent bea75b3389

commit 80e4c1cd42

3 changed files with 28 additions and 1 deletions

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19

arch/x86/Kconfig

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1

arch/x86/include/asm/cpufeatures.h

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9

arch/x86/include/asm/disabled-features.h

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