[Lguest] reserving interrupts

[Rusty Russell]

On Thu, 2007-08-30 at 09:24 -0700, ron minnich wrote:
> I thought I would drop this idea on the list so the kernel experts can
> tell me if this is ok.
> 
> Problem: I need to reserve a few interrupts for guests that use a
> SYSCALL_VECTOR other than 0x80. Currently, io_apic.c grabs just about
> every interrupt there is, although (on my laptop) it uses few of them.
> 
> I am thinking to use pre_setup_arch_hook for this. It would check for
> a list of values in a new reserved_interrupts parameter, and set a bit
> in a bitmask (reserved_interrupts).
> 
> In the i8259.c and io_apic.c code, the check for SYSCALL_VECTOR would
> remain, but an additional check against reserved_interrupts would be
> added, and any interrupts in that mask would not be used by the
> hardware.

IMHO you should use it for SYSCALL_VECTOR.  Initialize the bitmap early
with that set.

That makes it a cleanup and slight generalization, rather than a new
feature 8)

Rusty.