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 15:57:13 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Borislav Petkov <bp@...en8.de>,
	"Yu, Fenghua" <fenghua.yu@...el.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>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>
Subject: Re: [tip:x86/microcode] x86/microcode_intel_early.c: Early update
 ucode on Intel's CPU

On 12/11/2012 03:53 PM, Yinghai Lu wrote:
> On Tue, Dec 11, 2012 at 9:38 AM, H. Peter Anvin <hpa@...or.com> wrote:
>> On 12/11/2012 09:15 AM, Yinghai Lu wrote:
>>>
>>>
>>> No, that is not right place. initrd could be loaded anywhere like way
>>> high by bootloader.
>>>
>>
>> Only *after* your changes... the current protocol doesn't allow that.
> 
> before for-x86-boot change,
> 
> bootloader put ramdisk just under 2g...
> 
> [    0.000000] memblock_reserve: [0x7d9dc000-0x7fffefff] RAMDISK
> 
> and arch/x86/kernel/head_64.S only set ident mapping for [0,1g)
> 
> so before init_memory_mapping, we need to use early_ioremap to access
> ramdisk area.
> 
> also even after init_memory_mapping, we still need use early_ioremap to access
> it because user could use memmap to skip it.
> 
> PS: this problem have nothing to do with mapping that is set by bootloader.
> arch/x86/kernel/head_64.c will have it own mapping, and only cover [0,1g).
> 

Well, we could invoke it on the bootloader page tables, but as you say
it may not be a good idea... depending on how much memory we may be
talking about.  One solution -- which I have to admit is starting to
sound really good -- is to set up a #PF handler which cycles through a
set of page tables and creates a "virtual identity map"... it does have
the advantage of making the entire physical address space available
without any additional funnies.

	-hpa

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