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

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Message-ID: <20120531203544.GA19420@phenom.dumpdata.com>
Date:	Thu, 31 May 2012 16:35:44 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.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.

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.
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