linux-kernel - Re: [RFC][PATCH 03/17] x86/cpu: Make srso_untrain

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Message-ID: <20230810120004.GFZNTRRPGlJuSBy8Du@fat_crate.local>
Date:   Thu, 10 Aug 2023 14:00:04 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, David.Kaplan@....com,
        Andrew.Cooper3@...rix.com, jpoimboe@...nel.org,
        gregkh@...uxfoundation.org
Subject: Re: [RFC][PATCH 03/17] x86/cpu: Make srso_untrain_ret consistent

On Wed, Aug 09, 2023 at 09:12:21AM +0200, Peter Zijlstra wrote:
> This does change srso_untrain_ret a little to be more consistent with
> srso_alias_untrain_ret (and zen_untrain_ret). Specifically I made
> srso_untrain_ret tail-call the srso_return_thunk, instead of doing the
> call directly. This matches how srso_alias_untrain_ret amd
> zen_untrain_ret also tail-call their respective return_thunk.
> 
> If this is a problem this can be easily fixed and a comment added to
> explain -- but this way they all end with a tail-call to their own
> return-thunk, which is nice and consistent.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/x86/lib/retpoline.S |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/arch/x86/lib/retpoline.S
> +++ b/arch/x86/lib/retpoline.S
> @@ -262,7 +262,7 @@ SYM_INNER_LABEL(srso_safe_ret, SYM_L_GLO
>  	int3
>  	/* end of movabs */
>  	lfence
> -	call srso_safe_ret
> +	jmp srso_return_thunk
>  	int3
>  SYM_CODE_END(srso_safe_ret)
>  SYM_FUNC_END(srso_untrain_ret)

I don't see a problem with it but I'd let David comment here.

-- 
Regards/Gruss,
    Boris.

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