linux-kernel - Re: One (possible) x86 get_user

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Message-ID: <1296156476.15234.246.camel@laptop>
Date:	Thu, 27 Jan 2011 20:27:56 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Jan Beulich <JBeulich@...ell.com>,
	Xiaowei Yang <xiaowei.yang@...wei.com>,
	Nick Piggin <npiggin@...nel.dk>, fanhenglong@...wei.com,
	Kaushik Barde <kbarde@...wei.com>,
	Kenneth Lee <liguozhu@...wei.com>,
	linqaingmin <linqiangmin@...wei.com>, wangzhenguo@...wei.com,
	Wu Fengguang <fengguang.wu@...el.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	linux-kernel@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Avi Kivity <avi@...hat.com>
Subject: Re: One (possible) x86 get_user_pages bug

On Thu, 2011-01-27 at 10:27 -0800, Jeremy Fitzhardinge wrote:
> 
> So is there some way we can preserve the current scheme's benefits while
> making it a bit more general?  (If anyone else has non-IPI-based
> shootdown, it would be s390; is there some inspiration there?  An
> instruction perhaps?) 

Well, you can provide a xen gupf implementation based on rcu freed
page-tables like powerpc, sparc and s390 have.

But you'll have to change the mmu_gather implementation of xen and use
the get_page_unless_zero() thing mentioned before (or use
page_cache_get_speculative()).

But I see no need to change the x86 implementation, if the architecture
ever changes the way it does tlb invalidation we need to change more
than just the gupf implementation.


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