linux-kernel - Re: [PATCH v3 3/3] x86/retpoline: Convert generic specific retpolines to use RETPOLINE

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Message-ID: <e17565b1-3f51-3739-b788-d73063454436@amd.com>
Date:   Wed, 10 Jan 2018 08:23:25 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     "Woodhouse, David" <dwmw@...zon.co.uk>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "andi@...stfloor.org" <andi@...stfloor.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "pjt@...gle.com" <pjt@...gle.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "jikos@...nel.org" <jikos@...nel.org>,
        "gregkh@...ux-foundation.org" <gregkh@...ux-foundation.org>
Subject: Re: [PATCH v3 3/3] x86/retpoline: Convert generic specific retpolines
 to use RETPOLINE_GENERIC

On 1/10/2018 7:15 AM, Woodhouse, David wrote:
> On Tue, 2018-01-09 at 18:28 -0800, Andi Kleen wrote:
>> From: Andi Kleen <ak@...ux.intel.com>
>>
>> X86_FEATURE_RETPOLINE has been renamed to X86_FEATURE_RETPOLINE_GENERIC.
>> Convert the sequences using it.
> 
> AMD documentation says they need the RSB fill too, so these should stay
> under X86_FEATURE_RETPOLINE I think.

AMD processors don't fall back to the indirect predictor on an underflow
so this isn't needed on AMD if it is purely for underflow prevention.

Thanks,
Tom

> 
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