linux-kernel - Re: [PATCH v2 5/8] x86/speculation: Add basic support for IBPB

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Message-ID: <20180121190430.ss22poeakvwzvcal@pd.tnic>
Date:   Sun, 21 Jan 2018 20:04:30 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     arjan@...ux.intel.com, tglx@...utronix.de, karahmed@...zon.de,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com, peterz@...radead.org,
        pbonzini@...hat.com, ak@...ux.intel.com,
        torvalds@...ux-foundation.org, gregkh@...ux-foundation.org
Subject: Re: [PATCH v2 5/8] x86/speculation: Add basic support for IBPB

On Sun, Jan 21, 2018 at 06:54:22PM +0000, David Woodhouse wrote:
> Because we're backporting this to every stable kernel under the sun,
> and they don't already require asm-goto.

Considering the cost of the barrier, I'd simplify the whole endeavor
*considerably* for backporting:

	if (boot_cpu_has(X86_FEATURE_IBPB))
		wrmsr(MSR_IA32_PRED_CMD, PRED_CMD_IBPB, 0);

Problem solved.

Upstream can then do static_cpu_has() if it wants to.

-- 
Regards/Gruss,
    Boris.

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