Re: What happens if I use get_user_pages()

[Izik Eidus <izik@qumranet.com>]

ציטוט Arn:
>>> If I use the kernel function "get_user_pages()" within a guest
>>> kernel module, will this ensure that the guests pages are never
>>> swapped out by the host ? Will it lock these pages in memory ?
>>> (Has anyone tried this ? )
>>>       
>> As Izik said, the answer is no. Is this the desirable outcome, or are
>> you trying to find a way for the guest to force the host to pin pages
>> in memory? If so, why?
>>
>>     
>
> Izik, Muli, thanks,
>
> Actually I don't want the guests pages to be pinned at all. My aim is
> to do a timing check from within guest (guest kernel) to see if we can
> detect that the host has swapped out any of the guests pages. Without
> the guest knowing. Its proving to be more difficult than I had
> thought. Probably due to my lack of experience with kvm/linux
> internals.
>
> My idea is to get the guest kernel to read byte from each of its pages
> (either all or a random set of pages) and do a timing check at each
> read. A read from a page that has been swapped out by host should take
> much longer than a read done directly from memory.
>
> From previous emails on this list it seems that if I map a guest's
> page into its kernelspace then that page will never be swapped out
> (due to shadow pagetables). So now I'm stuck, any advice will be
> appreciated.
>   

pages that will be inside the shadow page tables wont be swappable, you 
have to use mmu notifiers patch in order to have reible swapping.

> thanks
> Arn
>