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

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Date:   Thu, 3 Nov 2022 10:31:30 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        openrisc@...ts.librecores.org,
        Michael Ellerman <mpe@...erman.id.au>,
        "open list:LINUX FOR POWERPC PA SEMI PWRFICIENT" 
        <linuxppc-dev@...ts.ozlabs.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH v3 2/2] x86: Fix /proc/cpuinfo cpumask warning

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@...il.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.