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

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Date:   Wed, 10 Jan 2018 00:43:11 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Tom Lendacky <thomas.lendacky@....com>
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 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.

Thanks,

	tglx