Re: [PATCH 4/6] scs: Move scs_overflow_check() out of architecture code

[Will Deacon]

On Mon, May 18, 2020 at 08:31:49AM -0700, Kees Cook wrote:
> On Mon, May 18, 2020 at 02:32:31PM +0100, Mark Rutland wrote:
> > On Mon, May 18, 2020 at 02:23:47PM +0100, Will Deacon wrote:
> > > This is something I would like to revisit, but we need more
> > > information from Sami about why Android rejected the larger allocation
> > > size, since I don't think there's an awful lot of point merging this
> > > series if Android doesn't pick it up.
> > 
> > Indeed. I'd certainly prefer the robustness of a VMAP'd SCS if we can do
> > that.
> 
> For smaller devices, the memory overhead was too high. (i.e. 4x more
> memory allocated to kernel stacks -- 4k vs 1k per thread.)

I just don't see an extra 3k per thread as being a real issue (the main
stack is 16k already). Even just the CPU register state is around 1k.

But I'd be very keen to see numbers/performance data that proves me wrong.

Will