linux-kernel - Re: virt_to_page for userspace pointers

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Message-ID: <4D58537C.3020409@rath.org>
Date:	Sun, 13 Feb 2011 16:56:12 -0500
From:	Nikolaus Rath <Nikolaus@...h.org>
To:	Brice Goglin <Brice.Goglin@...-lyon.org>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: virt_to_page for userspace pointers

On 02/13/2011 03:37 PM, Brice Goglin wrote:
> 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.

That's fine, I know that if the page is there at all then it has been
locked by a (different) kernel driver. Is there any way to find out what
I want?


Thanks,

   -Nikolaus

-- 
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