Xen devel - Sep 2006 - RE: [PATCH] enable port accesses with (almost) fullregister context

>From: Keir Fraser
>Sent: 2006年9月11日 9:19
>Would it be cleaner to allow dom0 to have really direct access to some
>I/O
>ports by allowing it to set a real I/O bitmap? I implemented I/O bitmaps
>via
>emulation mainly because it makes context switching faster and it is less
>of
>a pain to keep admin and guest bitmasks in sync if they are checked
>synchronously. But a direct dom0-only bitmap would be a bit easier:
>quick to
>turn on/off and no need to sync with admin bitmaps. Main downside is
>that
>it''ll slow down context-switch paths a little bit.
>
> -- Keir
>
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?

Thanks,
Kevin

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On 11/9/06 6:24 pm, "Tian, Kevin" <kevin.tian@intel.com> wrote:
> 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.

 -- Keir



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On 11/9/06 8:58 pm, "Keir Fraser" <Keir.Fraser@cl.cam.ac.uk>
wrote:
> On 11/9/06 6:24 pm, "Tian, Kevin" <kevin.tian@intel.com>
wrote:
> 
>> 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




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