linux-kernel - Re: [PATCH 3/4] x86/retpoline: Simplify vmexit_fill

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Date:   Fri, 26 Jan 2018 16:24:39 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        tim.c.chen@...ux.intel.com, pjt@...gle.com, jikos@...nel.org,
        gregkh@...ux-foundation.org, dave.hansen@...el.com,
        riel@...hat.com, luto@...capital.net,
        torvalds@...ux-foundation.org, ak@...ux.intel.com,
        keescook@...gle.com, peterz@...radead.org
Subject: Re: [PATCH 3/4] x86/retpoline: Simplify vmexit_fill_RSB()

On Fri, 2018-01-26 at 14:24 +0100, Borislav Petkov wrote:
> diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
> index 1908214b9125..b889705f995a 100644
> --- a/arch/x86/include/asm/asm-prototypes.h
> +++ b/arch/x86/include/asm/asm-prototypes.h
> @@ -38,4 +38,7 @@ INDIRECT_THUNK(dx)
>  INDIRECT_THUNK(si)
>  INDIRECT_THUNK(di)
>  INDIRECT_THUNK(bp)
> +asmlinkage void __fill_rsb_clobber_ax(void);
> +asmlinkage void __clr_rsb_clobber_ax(void);
>  #endif /* CONFIG_RETPOLINE */
> 

Dammit, have the IBM vowel-stealers escaped again? What was wrong with
'__clear_rsb_clobber_ax'?

> 
> -/*
> - * Google experimented with loop-unrolling and this turned out to be
> - * the optimal version — two calls, each with their own speculation
> - * trap should their return address end up getting used, in a loop.
> - */

Let's not lose that comment?

Other than that, I think it'll look OK when it's a sane patch on top of
my existing tree instead of incremental on your last one. Thanks.
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