linux-kernel - RE: [tip:x86/microcode] x86/microcode_intel_early.c: Early update ucode on Intel's CPU

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Date:	Tue, 11 Dec 2012 17:26:40 +0000
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	Yinghai Lu <yinghai@...nel.org>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...ux.intel.com" <hpa@...ux.intel.com>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: RE: [tip:x86/microcode] x86/microcode_intel_early.c: Early update
 ucode on Intel's CPU

> -----Original Message-----
> From: yhlu.kernel@...il.com [mailto:yhlu.kernel@...il.com] On Behalf Of
> Yinghai Lu
> Sent: Tuesday, December 11, 2012 9:16 AM
> To: Borislav Petkov; Yinghai Lu; H. Peter Anvin; Yu, Fenghua;
> mingo@...nel.org; linux-kernel@...r.kernel.org; tglx@...utronix.de;
> hpa@...ux.intel.com; linux-tip-commits@...r.kernel.org
> Subject: Re: [tip:x86/microcode] x86/microcode_intel_early.c: Early
> update ucode on Intel's CPU
> 
> On Tue, Dec 11, 2012 at 9:06 AM, Borislav Petkov <bp@...en8.de> wrote:
> > On Tue, Dec 11, 2012 at 09:00:55AM -0800, Yinghai Lu wrote:
> >> ok, then next question is how early it should be.
> >>
> >> before early_cpu_init/early_identify_cpu
> >>
> >> or just before check_bugs/identify_cpu
> >
> > Read the code. It's in x86_64_start_kernel on 64-bit.
> >
> 
> No, that is not right place. initrd could be loaded anywhere like way
> high by bootloader.
> 
> to make code simple, we should have following sequence in setup_arch
> 
> early_ioremap_init()
> early_update_microcode()...
> early_cpu_init()
> 
> early_update_microcode could use early_ioremap to access initrd ramdisk
> area.

The problem is mainly from 32-bit. We need to load microcode before paging is enabled (I'm changing load_ucode_intel_ap to be called before paging as well). That makes the coding not simple. It's better to load ucode as early as possible in 64-bit as well. I don't want to have two totally different sets of early loading ucode for 64-bit and 32-bit. 

Thanks.

-Fenghua
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