linux-kernel - Re: [PATCH] Fix VMI crash on boot in 2.6.27+ kernels

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Date:	Tue, 09 Dec 2008 17:48:57 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Zachary Amsden <zach@...are.com>,
	Huang Ying <ying.huang@...el.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	norman@...backs.co.uk,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg KH <gregkh@...e.de>,
	Alok Kataria <alokkataria1@...il.com>,
	Bruno Prémont <"bruno .premont"@restena.lu>,
	xl@...igned.net, dsd@...too.org
Subject: Re: [PATCH] Fix VMI crash on boot in 2.6.27+ kernels

Yinghai Lu wrote:
> 
> VMI initialiation can relocate the fixmap, causing early_ioremap
> to malfunction if it is initialized before the relocation.  The
> ioremap area is low enough in virtual address space that no actual
> collision occurs, however, because the pagetables for it were not
> allocated under VMI mode, the pagetable updates are dropped by
> the hypervisor as irrelevant, resulting in a crash on boot.
> 

I have mentioned in the past that I think the very concept of relocating
the fixmap to be utterly braindead.  Instead, I believe we should locate
it low in kernel space so it doesn't have to be relocated.  It's
unfortunately a relatively large change.

	-hpa
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