On Thu, Nov 05, 2020 at 02:29:49PM +0000, Mark Brown wrote: > On Thu, Nov 05, 2020 at 02:03:22PM +0000, Mark Rutland wrote: > > On Thu, Nov 05, 2020 at 01:41:42PM +0000, Mark Brown wrote: > > > > It isn't obvious to me why we don't fall through to trying the SMCCC > > > TRNG here if for some reason the v8.5-RNG didn't give us something. > > > Definitely an obscure possibility but still... > > > I think it's better to assume that if we have a HW RNG and it's not > > giving us entropy, it's not worthwhile trapping to the host, which might > > encounter the exact same issue. > > There's definitely a good argument for that, but OTOH it's possible the > SMCCC implementation is doing something else (it'd be an interesting > implementation decision but...). That said I don't really mind, I think > my comment was more that if we're doing this the code should be explicit > about what the intent is since right now it isn't obvious. Either a > comment or having an explicit "what method are we choosing" thing. > > > That said, I'm not sure it's great to plumb this under the > > arch_get_random*() interfaces, e.g. given this measn that > > add_interrupt_randomness() will end up trapping to the host all the time > > when it calls arch_get_random_seed_long(). > > > Is there an existing interface for "slow" runtime entropy that we can > > plumb this into instead? > > Yeah, I was wondering about this myself - it seems like a better fit for > hwrng rather than the arch interfaces but that's not used until > userspace comes up, the arch stuff is all expected to be quick. I > suppose we could implement the SMCCC stuff for the early variants of the > API you added so it gets used for bootstrapping purposes and then we > rely on userspace keeping things topped up by fetching entropy through > hwrng or otherwise but that feels confused so I have a hard time getting > enthusiastic about it. I'm perfectly happy for the early functions to call this, or for us to add something new firmwware_get_random_*() functions that we can call early (and potentially at runtime, but less often than arch_get_random_*()). I suspect the easy thing to do for now is plumb this into the existing early arch functions and hwrng. Thanks, Mark. _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
