[PATCH RFC v1 07/10] arm64: use sched_clock() for random_get_entropy() instead of zero

[Jason A. Donenfeld]

Hi Mark,

On Fri, Apr 08, 2022 at 07:33:53PM +0100, Mark Rutland wrote:
> On Fri, Apr 08, 2022 at 08:21:42PM +0200, Jason A. Donenfeld wrote:
> > In the event that random_get_entropy() can't access a cycle counter or
> > similar, falling back to returning 0 is really not the best we can do.
> > Instead, at least calling sched_clock() would be preferable, because
> > that always needs to return _something_, even falling back to jiffies
> > eventually. It's not as though sched_clock() is super high precision or
> > guaranteed to be entropic, but basically anything that's not zero all
> > the time is better than returning zero all the time.
> > 
> > If CONFIG_ARM_ARCH_TIMER=n, then get_cycles() will return 0, so we only
> > need the fallback code for that case.
> 
> In arch/arm64/Kconfig we unconditionally select CONFIG_ARM_ARCH_TIMER,
> so that configuration shouldn't be possible, and I don't think this
> patch is necessary.
> 
> On arm64 we depend on the architected timer in a bunch of places, so
> anyone hacking that out has bigger problems.

Thanks for the tip. I'll drop this patch from the series.

Jason