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xen-devel
[Xen-devel] Re: One (possible) x86 get_user_pages bug
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To: |
Jan Beulich <JBeulich@xxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: One (possible) x86 get_user_pages bug |
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From: |
Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> |
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Date: |
Thu, 27 Jan 2011 17:25:02 +0100 |
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Cc: |
Kaushik Barde <kbarde@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Kenneth Lee <liguozhu@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, wangzhenguo@xxxxxxxxxx, Xiaowei Yang <xiaowei.yang@xxxxxxxxxx>, linqaingmin <linqiangmin@xxxxxxxxxx>, fanhenglong@xxxxxxxxxx, Wu Fengguang <fengguang.wu@xxxxxxxxx> |
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Thu, 27 Jan 2011 18:54:46 -0800 |
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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..
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