linux-kernel - Re: [PATCH v1 1/2] x86/retpoline: Add a function to clear the RETPOLINE

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Message-ID: <ec9d4e6e-f6d9-1001-ed2e-ae242de88944@amd.com>
Date:   Tue, 9 Jan 2018 18:22:39 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Rik van Riel <riel@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jikos@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...gle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH v1 1/2] x86/retpoline: Add a function to clear the
 RETPOLINE_AMD feature

On 1/9/2018 5:43 PM, Thomas Gleixner wrote:
> On Tue, 9 Jan 2018, Tom Lendacky wrote:
>> On 1/9/2018 5:09 PM, Thomas Gleixner wrote:
>>> On Tue, 9 Jan 2018, Tom Lendacky wrote:
>>>> On 1/9/2018 4:46 PM, Thomas Gleixner wrote:
>>>>> Urgh. That's an awful hack. why not do the obvious?
>>>>
>>>> My first attempt was very similar to your change below, but testing
>>>> showed that spectre_v2_check_boottime_disable() is called before the
>>>> X86_FEATURE_LFENCE_RDTSC can be set.  I can look at moving where the
>>>> X86_FEATURE_LFENCE_RDTSC is set, maybe into early_init_amd() or such
>>>> if you think that would be best.
>>>
>>> Wait, we can move the selection _AFTER_ identify_boot_cpu().
>>
>> Much cleaner.  Since it's just a single patch now, do you want me to
>> re-submit this after I test it or will you just pick this up as is?
>>
>> I did notice that the patch does change the behavior associated with
>> the command line options, though.  Not sure if that was intentional.
> 
> Yes. I noticed while looking at your issue that when AMD is selected on the
> command line then we have no support at all on intel. So I prefer to err
> out and enable the generic version.
> 
> If you can just polish it up with a changelog and resubmit after testing
> that would be appreciated as I'm steam blasting the IBRS stuff at the
> moment.

Will do.  I'll add your Signed-off-by when I submit it.

Thanks,
Tom

> 
> Thanks,
> 
> 	tglx
>