Reminder: all Spectre, except v1 style, should be fully fixable, without trusting vendor ucode updates to do it right, by flushing whole cache hierarchy at every kernelspace entry and exit and turning off HT. Anyone tried this and measured cost?
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Replying to @RichFelker
Not sure about flushing at every context switch, but doing so whenever a different process is scheduled on a CPU (or core complex, when a complex shares L2) might make sense because there's probably some amount of eviction happening in such cases anyway.
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Replying to @siddhesh_p
Every entry/exit is needed to avoid kernel leaks if you don't trust mitigations on kernel side. Otherwise just at vm context switch is ok.
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Replying to @RichFelker @siddhesh_p
It would be nice to see both tested and compared.
10:46 AM - 26 Aug 2018
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