linux-kernel - Re: [PATCH 5/8] x86: Make old K8 swapgs workaround conditional

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Message-ID: <20150410231013.GD2366@two.firstfloor.org>
Date:	Sat, 11 Apr 2015 01:10:13 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Andi Kleen <andi@...stfloor.org>, x86@...nel.org, luto@...nel.org,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 5/8] x86: Make old K8 swapgs workaround conditional

On Sat, Apr 11, 2015 at 12:01:10AM +0200, Borislav Petkov wrote:
> > diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> > index a220239..e7f5667 100644
> > --- a/arch/x86/kernel/cpu/amd.c
> > +++ b/arch/x86/kernel/cpu/amd.c
> > @@ -551,6 +551,9 @@ static void init_amd_k8(struct cpuinfo_x86 *c)
> >  	if ((level >= 0x0f48 && level < 0x0f50) || level >= 0x0f58)
> >  		set_cpu_cap(c, X86_FEATURE_REP_GOOD);
> >  
> > +	/* Early steppings needed a mfence on swapgs. */
> > +	set_cpu_cap(c, X86_BUG_SWAPGS_MFENCE);
> 
> set_cpu_bug()
> 
> and this should not be set on all K8 but for the early steppings only
> which need it.

I don't know which one, but I don't think it really matters.

-Andi
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