linux-kernel - Re: 2.6.25-rc1 xen pvops regression

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Date:	Wed, 13 Feb 2008 22:59:33 +1100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jody Belka <lists-lkml@...b.org>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ian Campbell <ijc@...lion.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andi Kleen <andi@...stfloor.org>,
	Mika Penttila <mika.penttila@...umbus.fi>
Subject: Re: 2.6.25-rc1 xen pvops regression

Jody Belka wrote:
> Hi all,
>
> I thought I'd try out 2.6.25-rc1 as a xen 32-bit pae domU the other day.
> Unfortunately, I didn't get very far very fast, as the domain just crashed
> immediately upon booting, without any direct feedback (I did have messages
> on the xen message buffer, which helped). This even with earlyprintk turned on.
>
> After a long, arduous journey, I managed to track this down to the following:
>
> ----------
> commit	551889a6e2a24a9c06fd453ea03b57b7746ffdc0
>
> x86: construct 32-bit boot time page tables in native format.
>
> Specifically the boot time page tables in a CONFIG_X86_PAE=y enabled
> kernel are in PAE format.
>
> early_ioremap is updated to use the standard page table accessors.
>
> Clear any mappings beyond max_low_pfn from the boot page tables in
> native_pagetable_setup_start because the initial mappings can extend
> beyond the range of physical memory and into the vmalloc area.
>
> Derived from patches by Eric Biederman and H. Peter Anvin.
>
> [ jeremy@...p.org: PAE swapper_pg_dir needs to be page-sized fix ]
> ----------
>
> However, to make life more interesting, just reverting this isn't quite
> enough to get us to the promised land. If we try, we find that although
> we do now start booting, we crash again a short way into the process.
>
> In a different manner though. Specifically, in early_ioremap_clear.
> Reverting the above commit /except/ for the changes to arch/x86/mm/ioremap.c
> gets everything working again.
>
> Well, except that we can't shutdown/reboot properly, but I've sent a patch
> for that in another email.
>
>
> I'm afraid i've no idea what needs to be done to get the change to work
> with xen, but i'm willing to try out any patches people come up with.
> Please cc me on any replies, as i'm not subscribed, thanks.

Hi,

Although I'm on vacation, I happened to download a recent copy of 
x86.git and found that it crashes early.  Here's a couple of patches to 
apply; I don't know if they apply to current git, but I hope it helps.

    J

View attachment "x86-fix-early_ioremap.patch" of type "text/x-patch" (981 bytes)

View attachment "xen-unpin-init_pt.patch" of type "text/x-patch" (800 bytes)