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Date: Thu, 18 Jan 2018 11:44:53 -0800
From: Tim Chen <tim.c.chen@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: David Woodhouse <dwmw2@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>, linux-kernel@vger.kernel.org,
	Dave Hansen <dave.hansen@intel.com>,
	Ashok Raj <ashok.raj@intel.com>, Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Andi Kleen <ak@linux.intel.com>,
	Arjan Van De Ven <arjan.van.de.ven@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Asit Mallick <asit.k.mallick@intel.com>,
	Jason Baron <jbaron@akamai.com>,
	David Woodhouse <dwmw@amazon.co.uk>
Subject: Re: [PATCH 26/35] x86/enter: Create macros to stop/restart Indirect
 Branch Speculation
Message-ID: <20180118194452.GA6849@linux.intel.com>
Reply-To: tim.c.chen@linux.intel.com
References: <20180118134800.711245485@infradead.org>
 <20180118140153.015311385@infradead.org>
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On Thu, Jan 18, 2018 at 02:48:26PM +0100, Peter Zijlstra wrote:
> From: Tim Chen <tim.c.chen@linux.intel.com>
> 
> +
> +.macro STOP_IB_SPEC
> +	ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_IBRS

Peter,

Will it be possible to use static key here like
	STATIC_JUMP_IF_FALSE .Lskip_\@, specctrl_ibrs, def=0

In Thomas' original patchset, there is a specctrl_ibrs static key.

That will make a switch of static branch here easier if we want
to change it later in boot or at run time.

Tim 

> +	PUSH_MSR_REGS
> +	WRMSR_ASM $MSR_IA32_SPEC_CTRL, $0, $SPEC_CTRL_ENABLE_IBRS
> +	POP_MSR_REGS
> +.Lskip_\@:
> +.endm
> +