From: "Jan Beulich" <JBeulich@novell.com>
To: "Peter Zijlstra" <a.p.zijlstra@chello.nl>
Cc: "Jeremy Fitzhardinge" <jeremy@goop.org>, <fanhenglong@huawei.com>,
"Kaushik Barde" <kbarde@huawei.com>,
"Kenneth Lee" <liguozhu@huawei.com>,
"linqaingmin" <linqiangmin@huawei.com>, <wangzhenguo@huawei.com>,
"Xiaowei Yang" <xiaowei.yang@huawei.com>,
"Wu Fengguang" <fengguang.wu@intel.com>,
"Nick Piggin" <npiggin@kernel.dk>,
"xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
<linux-kernel@vger.kernel.org>
Subject: Re: One (possible) x86 get_user_pages bug
Date: Thu, 27 Jan 2011 16:41:37 +0000 [thread overview]
Message-ID: <4D41AE51020000780002ED8F@vpn.id2.novell.com> (raw)
In-Reply-To: <1296145502.15234.235.camel@laptop>
>>> On 27.01.11 at 17:25, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
> On Thu, 2011-01-27 at 16:07 +0000, Jan Beulich wrote:
>>
>> Nick, based on your doing of the initial implementation, would
>> you be able to estimate whether disabling get_user_pages_fast()
>> altogether for Xen would be performing measurably worse than
>> adding the locks (but continuing to avoid acquiring mm->mmap_sem)
>> as suggested by Xiaowei? That's of course only if the latter is correct
>> at all, of which I haven't fully convinced myself yet.
>
> Adding the lock will result in deadlocks, __get_user_pages_fast() is
> used from NMI context.
>
> Then again, I've got no clue if Xen even has NMIs..
It does, but not in a way that would be usable for perf events
afaict, so that code path should be dead under Xen. (We don't
even build the offending source file in our kernels, but I'm not
sure how pv-ops deals with situations like this - Jeremy?)
Jan
next prev parent reply other threads:[~2011-01-27 16:41 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-27 13:05 Xiaowei Yang
2011-01-27 13:56 ` Peter Zijlstra
2011-01-27 14:30 ` Jan Beulich
2011-01-28 10:51 ` Peter Zijlstra
2011-01-27 14:49 ` Jan Beulich
2011-01-27 15:01 ` Peter Zijlstra
2011-01-27 18:27 ` Jeremy Fitzhardinge
2011-01-27 19:27 ` Peter Zijlstra
2011-01-30 13:01 ` Avi Kivity
2011-01-30 22:21 ` Kaushik Barde
2011-01-31 18:04 ` Jeremy Fitzhardinge
2011-01-31 20:10 ` Kaushik Barde
2011-01-31 22:10 ` Jeremy Fitzhardinge
2011-01-27 16:07 ` Jan Beulich
2011-01-27 16:25 ` Peter Zijlstra
2011-01-27 16:41 ` Jan Beulich [this message]
2011-01-27 16:56 ` Peter Zijlstra
2011-01-27 21:24 ` Nick Piggin
2011-01-28 7:17 ` Xiaowei Yang
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