linux-kernel - Re: [PATCH] x86/i386: Check PSE bit before using PAGE_KERNEL

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Date:	Thu, 31 May 2012 16:02:11 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	konrad@...nok.org, linux-kernel@...r.kernel.org, x86@...nel.org,
	mingo@...hat.com, tglx@...utronix.de, stable@...nel.org
Subject: Re: [PATCH] x86/i386: Check PSE bit before using PAGE_KERNEL_LARGE.

No, PAE kernels cannot boot on non-PAE hardware.

Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:

>On Thu, May 31, 2012 at 01:21:02PM -0700, H. Peter Anvin wrote:
>> On 05/31/2012 12:40 PM, Konrad Rzeszutek Wilk wrote:
>> > During bootup we would unconditionally do this on any
>> > machine that was built with CONFIG_NUMA=y on i386:
>> > 
>> > setup_arch
>> >   \-initmem_init
>> >       \-x86_numa_init (with dummy_init as callback)
>> >           \- init_alloc_remap
>> >                \- set_pmd_pfn (with PAGE_PSE)
>> > 
>> > without checking to see if the CPU supports PSE. This
>> > patch adds that and also allows the init_alloc_remap function
>> > to properly work by falling back on PTEs.
>> > 
>> 
>> Well, the code looks like it is PAE-specific, and PAE implies PSE.
>
>I have to double check - but I think a kernel built with
>CONFIG_HIGHMEM64=y
>and CONFIG_NUMA=y would boot on a Pentium II which can't do PAE.
>
>But perhaps there are some other checks that would halt the kernel
>before it even got there?
>
>> 
>> Xen breaks that, but that is a divergence of Xen from x86.
>
>It certainly does <sigh>. And that is how I spotted this - b/c the
>PMD would fail (with tons of mutlicalls warnings) - and the PTE's
>would still point to the old PFNs.

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
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