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

From: Brian Gerst <brgerst@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Juergen Gross <jgross@suse.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Alexandre Chartre <alexandre.chartre@oracle.com>
Subject: Re: [patch part-III V2 05/23] x86/entry/32: Provide macro to emit IDT entry stubs
Date: Mon, 9 Mar 2020 01:08:35 -0400	[thread overview]
Message-ID: <CAMzpN2itqrztb+wA1k-KDwYMyQw3nZaMjzkHCu4GLr=t10ug=w@mail.gmail.com> (raw)
In-Reply-To: <20200308231718.931465601@linutronix.de>

On Sun, Mar 8, 2020 at 7:24 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> From: Thomas Gleixner <tglx@linutronix.de>
>
> 32 and 64 bit have unnecessary different ways to populate the exception
> entry code. Provide a idtentry macro which allows to consolidate all of
> that.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
>
> ---
>  arch/x86/entry/entry_32.S |   42 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
>
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -44,6 +44,7 @@
>  #include <asm/asm.h>
>  #include <asm/smap.h>
>  #include <asm/frame.h>
> +#include <asm/trapnr.h>
>  #include <asm/nospec-branch.h>
>
>  #include "calling.h"
> @@ -726,6 +727,47 @@
>
>  .Lend_\@:
>  .endm
> +
> +#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);
}

--
Brian Gerst