Re: Userspace MSR handling

[Gerd Hoffmann <kraxel@redhat.com>]

On 05/28/09 10:53, Avi Kivity wrote:
> Gerd Hoffmann wrote:
>> Trying to use in-kernel xen netback driver adds this problem:
>> * Host kernel does xen hypercalls. Ouch. We have to emulate them
>> in-kernel (otherwise using in-kernel netback would be a quite
>> pointless exercise).
>
> Or do the standard function pointer trick. Event channel notifications
> change to eventfd_signal, grant table ops change to copy_to_user().

grant table ops include mapping pages of the guest (aka domU) into the 
host (aka dom0) address space, fill the pointer into some struct (bio 
for blkback, skb for netback), send it down the road for processing. 
netback and blkback do quite some lowlevel xen memory management to get 
that done, including m2p and p2m table updates due to direct paging 
mode.  It isn't as easy as s/hypercall/get_user_pages/ ...

cheers,
   Gerd