linux-kernel - Re: [PATCH V2 9/9] x86/speculation: Remove all ANNOTATE_NOSPEC

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Date:   Thu, 9 Apr 2020 12:40:08 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexandre Chartre <alexandre.chartre@...cle.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, jthierry@...hat.com,
        tglx@...utronix.de
Subject: Re: [PATCH V2 9/9] x86/speculation: Remove all
 ANNOTATE_NOSPEC_ALTERNATIVE directives

On Thu, Apr 09, 2020 at 12:34:24PM +0200, Peter Zijlstra wrote:
> @@ -111,23 +83,21 @@
>   */
>  .macro JMP_NOSPEC reg:req
>  #ifdef CONFIG_RETPOLINE
> -	ANNOTATE_NOSPEC_ALTERNATIVE
> -	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *\reg),	\
> -		__stringify(RETPOLINE_JMP \reg), X86_FEATURE_RETPOLINE,	\
> -		__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *\reg), X86_FEATURE_RETPOLINE_AMD
> +	ALTERNATIVE "", "lfence", X86_FEATURE_RETPOLINE_AMD
> +	ALTERNATIVE __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
> +		    __stringify(jmp __x86_retpoline_\reg), X86_FEATURE_RETPOLINE

Still, I am being an idiot, only the call (below) needs this, this can
stay what it was:

+       ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
+                     __stringify(jmp __x86_retpoline_\()\reg), X86_FEATURE_RETPOLINE, \
+                     __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD

>  #else
> -	jmp	*\reg
> +	jmp	*%\reg
>  #endif
>  .endm
>  
>  .macro CALL_NOSPEC reg:req
>  #ifdef CONFIG_RETPOLINE
> -	ANNOTATE_NOSPEC_ALTERNATIVE
> -	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *\reg),	\
> -		__stringify(RETPOLINE_CALL \reg), X86_FEATURE_RETPOLINE,\
> -		__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *\reg), X86_FEATURE_RETPOLINE_AMD

And then this needs a comment on why it is not ALTERNATIVE_2 like above.

> +	ALTERNATIVE "", "lfence", X86_FEATURE_RETPOLINE_AMD
> +	ALTERNATIVE __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \
> +		    __stringify(call __x86_retpoline_\reg), X86_FEATURE_RETPOLINE
>  #else
> -	call	*\reg
> +	call	*%\reg
>  #endif
>  .endm