linux-kernel - Re: [PATCH] x86/speculation: Use AMD specific retpoline for inline asm on AMD

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Date:   Tue, 18 Sep 2018 15:03:16 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Zhenzhong Duan <zhenzhong.duan@...cle.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        konrad.wilk@...cle.com, x86@...nel.org, dwmw@...zon.co.uk,
        tglx@...utronix.de, Srinivas REDDY Eeda <srinivas.eeda@...cle.com>,
        bp@...e.de, hpa@...or.com, dhaval.giani@...cle.com
Subject: Re: [PATCH] x86/speculation: Use AMD specific retpoline for inline
 asm on AMD

> > In original code, it will go to "call *%[thunk_target]\n" while
> > we have set SPECTRE_V2_RETPOLINE_MINIMAL or
> > SPECTRE_V2_RETPOLINE_MINIMAL_AMD. Is this expected?
> 
> Yes, that is exactly right -- it does that with or without your change
> though.

Soryr, I wrote that before I noticed the CONFIG_RETPOLINE vs RETPOLINE
thing.

In any case, since retpoline capable compilers are widely available, I'm
all for making CONFIG_RETPOLINE hard depend on it. That minimal stuff
really is quite silly.