linux-kernel - Re: [PATCH 16/16] x86/entry/64: Move the IST stacks into cpu_entry

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Date:   Tue, 21 Nov 2017 07:33:56 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 16/16] x86/entry/64: Move the IST stacks into cpu_entry_area

On Mon, Nov 20, 2017 at 11:38 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Andy Lutomirski <luto@...nel.org> wrote:
>
>>  /* May not be marked __init: used by software suspend */
>>  void syscall_init(void)
>>  {
>> @@ -1627,7 +1637,7 @@ void cpu_init(void)
>>        * set up and load the per-CPU TSS
>>        */
>>       if (!oist->ist[0]) {
>> -             char *estacks = per_cpu(exception_stacks, cpu);
>> +             char *estacks = get_cpu_entry_area(cpu)->exception_stacks;
>>
>>               for (v = 0; v < N_EXCEPTION_STACKS; v++) {
>>                       estacks += exception_stack_sizes[v];
>
> This generates a new build warning:
>
>  /home/mingo/tip/arch/x86/kernel/cpu/common.c: In function ‘syscall_init’:
>  /home/mingo/tip/arch/x86/kernel/cpu/common.c:1443:6: warning: unused variable ‘cpu’ [-Wunused-variable]
>    int cpu = smp_processor_id();
>
> because 'cpu' is now unused in the !CONFIG_IA32_EMULATION part.
>
> The naive fix is something like the patch below, untested.

I don't think I get this warning (at least not on my latest tree), but
there's an obvious cleanup to the earlier SYSCALL trampoline patch
that makes cpu be definitely used.