Re: [Xen-devel] real-mode switch

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 6/6/07 08:08, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> The problems with real mode code execution after initial boot is that once
> interrupts and certain types of exceptions got enabled, they would need
> to be masked over an unbounded time period, risking either losing of them
> or failing to handle them in time. On SMP systems, this would include either
> halting all remote CPUs or gracefully dealing with IPIs that may be sent
> against the CPU switching to or being in real mode (again over an
> unbounded period of time).

Also, it is usual to execute BIOS calls with interrupts enabled. That's
obviously bogus if protected-mode drivers have taken over devices, interrupt
vectors have been remapped, etc.

So we're going to return to real mode only at beginning of Xen execution,
and then down the road we'll come up with a scheme to avoid needing to do
that in cases like kexec of Xen (if anyone cares).

 -- Keir


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