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IOW wouldn't we better clear >> the other bit explicitly? (Due to the EIBRS dependency or RRSBA I think >> this can really only happen when the tool stack requests RSBA+EIBRS, as >> the deep deps clearing doesn't know the concept of "negative" >> dependencies.) > Hmm - I think there is a bug here, but it's not this simple.  I think > the only reasonable thing we can do is start rejecting bad input because > I don't think Xen can fix up safely. > > Xen must not ever clear RSBA, or we've potentially made the VM unsafe > behind the toolstack's back. > > If EIBRS != RRSBA, the toolstack has made a mistake.  Equally too for > RSBA && EIBRS. > > I think this is going to take more coffee to solve... Actually, no. I'm going to delete the hunk modifying recalculate_cpuid(), and move this patch back to the meaning it had in v1 which is just "get the policies looking correct". It's still not supported for the toolstack to request ARCH_CAPS (the "a" marking), and the safely logic for that can come in a subsequent series along with the unit(ish) testing I was already planning to do. ~Andrew