linux-kernel - Re: [PATCH 3/6] KVM: MMU: introduce gfn_to_page_atomic() and gfn_to_pfn

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Message-ID: <4C189C20.2070804@redhat.com>
Date:	Wed, 16 Jun 2010 12:40:48 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>,
	Huang Ying <ying.huang@...el.com>
Subject: Re: [PATCH 3/6] KVM: MMU: introduce gfn_to_page_atomic() and	gfn_to_pfn_atomic()

On 06/16/2010 11:49 AM, Andi Kleen wrote:
>> The page is fine, the page tables are not.  Another task can munmap() the
>> thing while is_hwpoison_address() is running.
>>      
> Ok  that boils down to me not seeing that source.
>
> If it accesses the page tables yes then it's racy. But whoever
> looked up the page tables in the first place should have
> returned an -EFAULT. There's no useful address attached
> to poison.
>    

We need to distinguish between genuine -EFAULT and poisoned address.

That's why I suggested get_user_pages_ptes_fast.  You can return page = 
NULL (-EFAULT) and the pte in the same go.  No race, and useful for 
other cases.

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

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