From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: how to deal with copy_to_user returning non zero
Date: Mon, 10 Nov 2014 10:04:08 +0000
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To: Anh Dinh <ug93tad@gmail.com>
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On Sun, 2014-11-09 at 09:22 +0800, Anh Dinh wrote:
> Thanks,
> 
> 
> I've found out the reason it page-faulting is because I used malloc()
> to allocate the output buffer, which turns out to allocate lazily.
> Therefore the hypervisor page-fault because the memory is still
> waiting to be mapped by the kernel. 
> 
> 
> I simply touched all the allocated memory, and it works fine now. 

It might work, but unless it is using hypercall buffers and
XEN_GUEST_HANDLE then it is still subtly broken.

Ian.