linux-kernel - Re: [patch part-III V2 05/23] x86/entry/32: Provide macro to emit IDT entry stubs

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Message-ID: <874kuy811k.fsf@nanos.tec.linutronix.de>
Date:   Mon, 09 Mar 2020 08:01:11 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Brian Gerst <brgerst@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>
Subject: Re: [patch part-III V2 05/23] x86/entry/32: Provide macro to emit IDT entry stubs

Brian Gerst <brgerst@...il.com> writes:
> On Sun, Mar 8, 2020 at 7:24 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>> +#ifdef CONFIG_X86_INVD_BUG
>> +.macro idtentry_push_func vector cfunc
>> +       .if \vector == X86_TRAP_XF
>> +               /* AMD 486 bug: invd from userspace calls exception 19 instead of #GP */
>> +               ALTERNATIVE "pushl      $do_general_protection",        \
>> +                           "pushl      $do_simd_coprocessor_error",    \
>> +                           X86_FEATURE_XMM
>> +       .else
>> +               pushl $\cfunc
>> +       .endif
>> +.endm
>> +#else
>> +.macro idtentry_push_func vector cfunc
>> +       pushl $\cfunc
>> +.endm
>> +#endif
>
> IMHO it would be better to push this to the C code and not make the
> asm more complicated.  Something like:
>
> dotraplinkage void
> do_simd_coprocessor_error(struct pt_regs *regs, long error_code)
> {
> #ifdef CONFIG_X86_INVD_BUG
>         /* AMD 486 bug: invd from userspace calls exception 19 instead of #GP */
>         if (!static_cpu_has(X86_FEATURE_XMM)) {
>                 do_general_protection(regs, error_code);
>                 return;
>         }
> #endif
>         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
>         math_error(regs, error_code, X86_TRAP_XF);
> }

That's too obvious :)

Thanks for catching that!

       tglx