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

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Message-ID: <4D456139.4090508@redhat.com>
Date:	Sun, 30 Jan 2011 15:01:45 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Jan Beulich <JBeulich@...ell.com>,
	Xiaowei Yang <xiaowei.yang@...wei.com>,
	Nick Piggin <npiggin@...nel.dk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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>
Subject: Re: One (possible) x86 get_user_pages bug

On 01/27/2011 08:27 PM, Jeremy Fitzhardinge wrote:
> And even just considering virtualization, having non-IPI-based tlb
> shootdown is a measurable performance win, since a hypervisor can
> optimise away a cross-VCPU shootdown if it knows no physical TLB
> contains the target VCPU's entries.  I can imagine the KVM folks could
> get some benefit from that as well.

It's nice to avoid the IPI (and waking up a cpu if it happens to be 
asleep) but I think the risk of deviating too much from the baremetal 
arch is too large, as demonstrated by this bug.

(well, async page faults is a counterexample, I wonder if/when it will 
bite us)

-- 
error compiling committee.c: too many arguments to function

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