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

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Message-ID: <1c6ca05f-094e-03e9-b21a-866aaf80cebb@oracle.com>
Date:   Tue, 18 Sep 2018 20:04:44 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:     Peter Zijlstra <peterz@...radead.org>
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

On 2018/9/18 18:59, Peter Zijlstra wrote:
> On Tue, Sep 18, 2018 at 06:31:07PM +0800, Zhenzhong Duan wrote:
>> On 2018/9/18 17:50, Peter Zijlstra wrote:
>>> On Mon, Sep 17, 2018 at 10:17:30PM -0700, Zhenzhong Duan wrote:
>>>> -#elif defined(CONFIG_X86_32) && defined(CONFIG_RETPOLINE)
>>>> +#elif defined(CONFIG_RETPOLINE)
>>>
>>> This doesn't make any sense..
>> This change is used for x86_64 to have minimal Retpoline support when
>> CONFIG_RETPOLINE is defined but RETPOLINE isn't defined, or I missed
>> something?
> 
> No it doesn't.
> 
> #if defined(X86_64) && defined(RETPOLINE)
> 
>   /* x86_64 retpoline goes here */
> 
> #elif defined(RETPOLINE)
> 
>   /* !x86_64 retpoline goes here */
> 
> #else
> 
>   /* !retpoline goes here
> 
> #endif

Sorry, but I am confused.
So where is 'if defined(x86_64) && !defined(RETPOLINE) && 
defined(CONFIG_RETPOLINE)' go?
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?

Thanks
Zhenzhong