RE: [Xen-devel] question on get_page_and_type()

["Santos, Jose Renato G" <joserenato.santos@xxxxxx>]

Ah, OK. Thanks for clarifying!
I assume this could only happen if the guest is buggy, right? Normally
the guest should not do a grant_copy into its pagetables or issue a
grant for its page tables. But in case it does it is only corrupting
itself right? I assume only the page owner could use the page for page
tables. Is it fair to say that the get_page_and_type() is only
protecting a guest to harm itself? In that case would it be acceptable
to transfer this enforcement to the guest itself if this gives a boost
in performance?

Thanks

Renato

> -----Original Message-----
> From: Ian Pratt [mailto:Ian.Pratt@xxxxxxxxxxxx] 
> Sent: Friday, April 13, 2007 8:15 PM
> To: Santos, Jose Renato G; xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: ian.pratt@xxxxxxxxxxxx
> Subject: RE: [Xen-devel] question on get_page_and_type()
> 
> 
> > Could someone please explain the following What is the purpose of 
> > get_page_and_type(page, domain,
> > PGT_writable_page) and why is it needed when doing a grant copy in 
> > __gnttab_copy()?
> > Why can't we just use get_page() to prevent the page from 
> being freed 
> > while we are doing the copy?
> 
> You don't want guests receiving data into pages containing 
> pagetables, hence we make sure we can get the page as a 
> writeable page.
> 
> Ian
>  
> 

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