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

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Date:	Thu, 21 Feb 2008 14:23:03 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ian Campbell <ijc@...lion.org.uk>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Joel Becker <Joel.Becker@...cle.com>,
	Jody Belka <lists-lkml@...b.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"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

Ian Campbell wrote:
> On Thu, 2008-02-21 at 13:37 -0800, Jeremy Fitzhardinge wrote:
>> H. Peter Anvin wrote:
>>>> Still curious about why a pagetable page is ending up in that range 
>>>> though.  Seems like it shouldn't be possible, since we shouldn't be 
>>>> allowed to allocate from those pages, at least until the DMI probe 
>>>> has happened...  Unless the early allocator is only excluded from 
>>>> e820 reserved pages, which would cause a problem on systems which 
>>>> don't reserve the DMI space...  HPA?
>>>>
>>> I thought the problem was a Xen-provided pagetable from before Linux 
>>> started? 
>> Hm, I don't think so.  The domain-builder pagetable is put after the 
>> kernel, so it shouldn't be under 1M.
> 
> I can confirm that it is Linux which is allocating it. The call path:
>         # xm create -c debian-x86_32p-1
>         Using config file "/etc/xen/debian-x86_32p-1".
>         Started domain debian-1
>         xen_alloc_pt_init PFN f0
>         Pid: 0, comm: swapper Not tainted 2.6.25-rc2 #68
>          [<c02ecb6b>] xen_alloc_pt_init+0x4b/0x60
>          [<c02f5e2b>] one_page_table_init+0x8b/0xf0
>          [<c02f63df>] paging_init+0x3bf/0x520
>          [<c02ee444>] setup_arch+0x2a4/0x410
>          [<c02e9a64>] start_kernel+0x64/0x380
>          [<c02efd7f>] cpu_detect+0x6f/0xf0
>          [<c02ed1a1>] xen_start_kernel+0x2f1/0x310
>          =======================
>         Entering add_active_range(0, 0, 262144) 0 entries of 256 used
>         Zone PFN ranges:
>           DMA             0 ->     4096
> 

What is the e820 information you feed the kernel?  We should only ever 
allocate page tables out of available RAM, not any other type of memory 
(reserved or not).

	-hpa
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