RE: [Xen-devel] [PATCH] enable port accesses with (almost) fullregister context

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
>Sent: 2006年9月11日 13:05
>>
>>> Hi, Keir,
>>> Say in the driver domain case, does dom0-only bitmap need to sync
>with admin
>>> bitmaps? Or simply depend on the assumption that dom0 won't use io
>ports
>>> granted to other domains?
>>
>> There's no checking of that kind of thing already. Xen will happily allow
>> I/O memory and I/O ports to be assigned write access for multiple
>domains
>> simultaneously. It's up to control tools, or a sysadmin, to implement or
>> enforce a more sophisticated policy if that is what is wanted.
>
>Maybe I misunderstood the question. If control tools update an admin
>bitmap
>today, then future port accesses by the guest are affected. If this dom0
>special bitmap is implemented, it is probably the case that we will not
>filter it through dom0's admin bitmap. As you say, we'll assume that
>special
>ports wouldn't be assigned to other domU's anyway.
>
> -- Keir

Yes, this assumption can ensure minimal performance affect. But, say in any 
case you still need to sync this special dom0 bitmap with guest bitmap, how 
much extra overhead to pay syncing with admin bitmap too? If not obviously 
differ, filtering all bitmaps can provide a more flexible interface for port 
assignment. :-)

Thanks,
Kevin

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