Re: [PATCH v3 2/2] x86: Fix /proc/cpuinfo cpumask warning

[Yury Norov <yury.norov@gmail.com>]

On Thu, Nov 03, 2022 at 05:49:06PM +0100, Borislav Petkov wrote:
> On Thu, Nov 03, 2022 at 09:30:54AM -0700, yury.norov@gmail.com wrote:a
> > Callers should pass sane arguments into internal functions if they
> > expect sane output.
> 
> What internal function? It's in a global header.
> 
> > The API not exported to userspace shouldn't sanity-check all inputs
> > arguments.
> 
> That doesn't have anything to do with userspace at all.
> 
> APIs exported to the rest of the kernel should very well check their
> inputs. Otherwise they're not APIs - just some random functions which
> are visible to the compiler.

Let's take for example cpu_llc_shared_mask() added by you in
arch/x86/include/asm/smp.h recently:

  static inline struct cpumask *cpu_llc_shared_mask(int cpu)
  {
         return per_cpu(cpu_llc_shared_map, cpu);
  }

It's in a global header and available to the rest of the kernel, just as
well. How does it check its input? Maybe I lost something important in
per_cpu() internals, but at the first glance, there's no any protection
against -1, nr_cpu_ids, and other out-of-range arguments.