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Subject: Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to enable/disable
 SPEC_CTRL feature
To: Tim Chen <tim.c.chen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>
References: <cover.1515204614.git.tim.c.chen@linux.intel.com>
 <b77c0cfc2d50ebdaa721f95012fd735cc374f04c.1515204614.git.tim.c.chen@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        linux-kernel@vger.kernel.org
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <d7413d40-7581-a994-5185-9f11c014cb0f@intel.com>
Date: Fri, 5 Jan 2018 19:12:12 -0800
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On 01/05/2018 06:12 PM, Tim Chen wrote:
>  .macro ENABLE_IBRS
> -	ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_SPEC_CTRL
> +	testl	$1, dynamic_ibrs
> +	jz	.Lskip_\@

There was an earlier suggestion to use STATIC_JUMP_IF_... here.  That's
a good suggestion, but we encountered some issues with it either
crashing the kernel at boot or not properly turning on/off.

We would love to do that minor really soon, but we figured everyone
would rather see this version than wait for us to debug such a minor tweak.