[SeaBIOS] [Xen-devel] Ideas for PV on SeaBIOS

James Harper james.harper at bendigoit.com.au
Thu May 19 11:32:04 CEST 2011

> >>> On 19.05.11 at 07:33, Daniel Castro <evil.dani at gmail.com> wrote:
> > In order to give PV Drivers to SeaBIOS we will need to solve a few
> > problems, one is the following:
> > Does a booting kernel informs the BIOS that it will leave real mode
> > and not use it again? When the booting kernel uses CPU real mode for
> > the last time, how can we (Xen or SeaBIOS) know that real mode will
> > longer be used, and hence BIOS calls will not be issued?
> > We want upon last real mode usage to leave all Xen PV information in
> > clean state, this means, closing the channel and ring between the
> > newly created domain and the host system.
> How can you be certain an OS won't switch back to real mode even
> after an extended period of up-time? Or that such switching back
> would affect you (could be calling e.g. the video or PCI BIOS
> functions only).

Well that's a problem with any device with a real mode counterpart (eg
INT13 for storage) isn't it? so just handle it in the same way.


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