linux-kernel - Re: [PATCH] x86/cpuid: Fix up "virtual" IBRS/IBPB/STIBP feature bits on Intel

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Message-ID: <alpine.DEB.2.20.1801301136590.1797@nanos>
Date:   Tue, 30 Jan 2018 11:37:49 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Woodhouse <dwmw@...zon.co.uk>
cc:     arjan@...ux.intel.com, karahmed@...zon.de, x86@...nel.org,
        linux-kernel@...r.kernel.org, tim.c.chen@...ux.intel.com,
        bp@...en8.de, peterz@...radead.org, pbonzini@...hat.com,
        ak@...ux.intel.com, torvalds@...ux-foundation.org,
        gregkh@...ux-foundation.org
Subject: Re: [PATCH] x86/cpuid: Fix up "virtual" IBRS/IBPB/STIBP feature bits
 on Intel

On Mon, 29 Jan 2018, David Woodhouse wrote:

> Despite the fact that all the other code there seems to be doing it,
> just using set_cpu_cap() in early_intel_init() doesn't actually work.
> 
> When the CPU is queried again in identify_boot_cpu(), it all gets
> overwritten again. Do it in init_scattered_cpuid_features() instead.
> 
> Turning the bits off for bad microcode can use setup_clear_cpu_cap()
> to force them off for all CPUs; I was less keen on forcing the feature
> bits *on* that way.
> 
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> Fixes: 2961298e ("x86/cpufeatures: Clean up Spectre v2 related CPUID flags")
> ---
> I feel I must be missing something. Is the rest of early_init_intel() broken too?

A lot of that stuff is duct taped and works more by chance than by
design. Borislav is looking into cleaning that up already.

Thanks,

	tglx