Message-ID: <479A5689.80505@zytor.com>
Date: Fri, 25 Jan 2008 13:37:13 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Jeremy Fitzhardinge <jeremy@goop.org>
CC: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Andi Kleen <ak@suse.de>, Jan Beulich <jbeulich@novell.com>,
       Eduardo Pereira Habkost <ehabkost@redhat.com>,
       Ian Campbell <ijc@hellion.org.uk>, William Irwin <wli@holomorphy.com>,
       Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 11 of 11] x86: defer cr3 reload when doing pud_clear()
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Jeremy Fitzhardinge wrote:
> PAE mode requires that we reload cr3 in order to guarantee that
> changes to the pgd will be noticed by the processor.  This means that
> in principle pud_clear needs to reload cr3 every time.  However,
> because reloading cr3 implies a tlb flush, we want to avoid it where
> possible.

It only matters (for a processor which supports PGE) if we actually use 
the namespace in between.

> In huge_pmd_unshare, it is followed by flush_tlb_range, which always
> results in a full cr3-reload tlb flush.

This one makes me nervous, as it feels like a side effect of 
implementation, and not a guarantee by design.

	-hpa
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