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Date: Mon, 17 Dec 2012 17:03:50 +0000
From: "Jan Beulich" <JBeulich@suse.com>
To: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: "Arnd Bergmann" <arnd@arndb.de>, "Ingo Molnar" <mingo@elte.hu>,
        "Michael Kerrisk" <mtk.manpages@gmail.com>,
        "Guennadi Liakhovetski" <g.liakhovetski@gmx.de>,
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        "Markus Trippelsdorf" <markus@trippelsdorf.de>,
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Subject: Re: [GIT PULL] x86/uapi for 3.8
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>>> On 17.12.12 at 17:39, "H. Peter Anvin" <hpa@linux.intel.com> wrote:
> Right, I think you nailed this one.  This patch copies PTEs from the
> kernel PTEs and thus they will have the global bit set.  It obviously
> makes no sense to *copy* PTEs from the kernel and yet leaving the global
> bit set, which means there are two ways of fixing it: either sharing
> page tables and use the cr4.pge off/on trick that Jan mentioned -- this
> would also be my preference -- and the other is to copy the PTEs but
> strip the global bit, which has the advantage that the actual kernel
> mappings will survive.

PTE copying is only one half of it. I think additionally L4 entries
get copied for the 1:1 mapping, and you can't strip the global
bits there without allocating separate page tables.

Jan