linux-kernel - Re: virt_to_page for userspace pointers

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Message-ID: <4D5840F6.8030401@ens-lyon.org>
Date:	Sun, 13 Feb 2011 21:37:10 +0100
From:	Brice Goglin <Brice.Goglin@...-lyon.org>
To:	Nikolaus Rath <Nikolaus@...h.org>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: virt_to_page for userspace pointers

Le 13/02/2011 21:24, Nikolaus Rath a écrit :
> On 02/05/2011 04:36 PM, Brice Goglin wrote:
>   
>>> Is there an equivalent function to virt_to_page (and virt_to_phys) that
>>> works with userspace pointers? Or do I have to manually walk through the
>>> page tables? In the later case, are there any examples of this kind of
>>> search that I could use as a basis?
>>>   
>>>       
>> You probably want get_user_pages() (or get_user_pages_fast()).
>>     
> Thanks for the pointer, that already helped a lot!
>
> I would, however, prefer a more primitive function that just gives me
> the struct page without locking it. And if the page is swapped out, I'd
> rather get a NULL pointer than having a page frame allocated.  Is there
> anything like that?
>   

If you don't lock the page, you have no guarantee that it won't get
swapped out or migrated while you look at the physical page.

Brice

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