On Thu, 12 Dec 2019 at 12:45, Marc Zyngier <maz@xxxxxxxxxx> wrote: > > On 2019-12-12 05:13, Neal Liu wrote: > > On Tue, 2019-12-03 at 11:17 +0000, Marc Zyngier wrote: > >> On 2019-12-03 04:16, Florian Fainelli wrote: > >> > On 12/2/2019 11:11 AM, Marc Zyngier wrote: > >> >> On Mon, 2 Dec 2019 16:12:09 +0000 > >> >> Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote: > >> >> > >> >>> (adding some more arm64 folks) > >> >>> > >> >>> On Fri, 29 Nov 2019 at 11:30, Neal Liu <neal.liu@xxxxxxxxxxxx> > >> >>> wrote: > >> >>>> > >> >>>> On Fri, 2019-11-29 at 18:02 +0800, Lars Persson wrote: > >> >>>>> Hi Neal, > >> >>>>> > >> >>>>> On Wed, Nov 27, 2019 at 3:23 PM Neal Liu > >> <neal.liu@xxxxxxxxxxxx> > >> >>>>> wrote: > >> >>>>>> > >> >>>>>> For MediaTek SoCs on ARMv8 with TrustZone enabled, > >> peripherals > >> >>>>>> like > >> >>>>>> entropy sources is not accessible from normal world (linux) > >> and > >> >>>>>> rather accessible from secure world (ATF/TEE) only. This > >> driver > >> >>>>>> aims > >> >>>>>> to provide a generic interface to ATF rng service. > >> >>>>>> > >> >>>>> > >> >>>>> I am working on several SoCs that also will need this kind of > >> >>>>> driver > >> >>>>> to get entropy from Arm trusted firmware. > >> >>>>> If you intend to make this a generic interface, please clean > >> up > >> >>>>> the > >> >>>>> references to MediaTek and give it a more generic name. For > >> >>>>> example > >> >>>>> "Arm Trusted Firmware random number driver". > >> >>>>> > >> >>>>> It will also be helpful if the SMC call number is > >> configurable. > >> >>>>> > >> >>>>> - Lars > >> >>>> > >> >>>> Yes, I'm trying to make this to a generic interface. I'll try > >> to > >> >>>> make > >> >>>> HW/platform related dependency to be configurable and let it > >> more > >> >>>> generic. > >> >>>> Thanks for your suggestion. > >> >>>> > >> >>> > >> >>> I don't think it makes sense for each arm64 platform to expose > >> an > >> >>> entropy source via SMC calls in a slightly different way, and > >> model > >> >>> it > >> >>> as a h/w driver. Instead, we should try to standardize this, and > >> >>> perhaps expose it via the architectural helpers that already > >> exist > >> >>> (get_random_seed_long() and friends), so they get plugged into > >> the > >> >>> kernel random pool driver directly. > >> >> > >> >> Absolutely. I'd love to see a standard, ARM-specified, > >> virtualizable > >> >> RNG that is abstracted from the HW. > >> > > >> > Do you think we could use virtio-rng on top of a modified > >> virtio-mmio > >> > which instead of being backed by a hardware mailbox, could use > >> > hvc/smc > >> > calls to signal writes to shared memory and get notifications via > >> an > >> > interrupt? This would also open up the doors to other virtio uses > >> > cases > >> > beyond just RNG (e.g.: console, block devices?). If this is > >> > completely > >> > stupid, then please disregard this comment. > >> > >> The problem with a virtio device is that it is a ... device. What we > >> want > >> is to be able to have access to an entropy source extremely early in > >> the > >> kernel life, and devices tend to be available pretty late in the > >> game. > >> This means we cannot plug them in the architectural helpers that Ard > >> mentions above. > >> > >> What you're suggesting looks more like a new kind of virtio > >> transport, > >> which is interesting, in a remarkably twisted way... ;-) > >> > >> Thanks, > >> > >> M. > > > > In conclusion, is it helpful that hw_random has a generic interface > > to > > add device randomness by talking to hwrng which is implemented in the > > firmware or the hypervisor? > > For most chip vendors, I think the answer is yes. We already prepared > > a > > new patchset and need you agree with this idea. > > As long as it is a *unified* interface, I'm all for that. > Yeah, but I'm not sure it makes sense to model it as a device like this. It would be nice if we could tie this into the ARM SMCCC discovery, and use the SMC calls to back arch_get_random_seed_long() [provided we fix the braindead way in which that is being used today in the interrupt code]
