linux-kernel - Re: Geode LX boot fails after x86 microcode revision change

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Date:	Thu, 10 Nov 2011 18:35:27 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Borislav Petkov <bp@...64.org>
CC:	Daniel Drake <dsd@...top.org>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Geode LX boot fails after x86 microcode revision change

On 11/09/2011 11:04 PM, Borislav Petkov wrote:
> On Tue, Nov 08, 2011 at 04:59:05PM -0600, Daniel Drake wrote:
>> On Tue, Nov 8, 2011 at 4:37 PM, Borislav Petkov <bp@...en8.de> wrote:
>>> Yep, just send me /proc/cpuinfo from a working kernel.
> 
> Daniel, would you please test? It should work though :-)
> 
> Thanks.
> 
> --
> From daa04c94628d5686404bd6985d4545f12c2fa4fd Mon Sep 17 00:00:00 2001
> From: Borislav Petkov <borislav.petkov@....com>
> Date: Wed, 9 Nov 2011 18:08:40 +0100
> Subject: [PATCH] x86, microcode, AMD: Restrict microcode reporting
> 
> bcb80e53877c ("x86, microcode, AMD: Add microcode revision to
> /proc/cpuinfo") added support for dumping microcode patch level in
> /proc/cpuinfo on AMD. Although we were very cautious and did rdmsr_safe
> on the microcode patch level MSR, this broke booting on Geode LX because
> this CPU doesn't have that MSR and at the time we do the read, exception
> tables which are used by rdmsr_safe are not yet initialized, leading to
> a boot hang.
> 
> This is the simple fix which enables the microcode line in /proc/cpuinfo
> for K8 and newer (it is not that interesting for older boxes anyway
> :-)).
> 
> Reported-and-bisected-by: Daniel Drake <dsd@...top.org>
> Link: http://lkml.kernel.org/r/CAMLZHHTSuHZoPbm_YfB8G05JA+xKCE4+Jmj4NW8mnZUHogQSBA@mail.gmail.com
            ^^^^^
I couldn't open this web-page!

Thanks,
Srivatsa S. Bhat

> Signed-off-by: Borislav Petkov <borislav.petkov@....com>
> ---
>  arch/x86/kernel/cpu/amd.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index c7e46cb..a72d183 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -474,7 +474,8 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
>  	}
>  #endif
> 
> -	rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);
> +	if (c->x86 >= 0xf)
> +		rdmsr_safe(MSR_AMD64_PATCH_LEVEL, &c->microcode, &dummy);
>  }
> 
>  static void __cpuinit init_amd(struct cpuinfo_x86 *c)

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