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

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Date:   Tue, 18 Sep 2018 22:41:10 +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 21:00, Peter Zijlstra wrote:
> On Tue, Sep 18, 2018 at 08:04:44PM +0800, Zhenzhong Duan wrote:
>> 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?
> Argh, CONFIG_RETPOLINE vs RETPOLINE :/
> 
> The thing is, the one you modify has a comment on that explains why it
> is i386 only. CET and retpolines don't like one another much.
> 
> And the x86_64 version uses %V which requires new GCC.
> 
> So I'm all for fixing the RETPOLINE_AMD thing, but at this point nobody
> should use the minimal stuff, that's just delusional.
> 

Clear, thanks for your explanation.

Zhenzhong