Re: [RFC KVM 18/27] kvm/isolation: function to copy page table entries for percpu buffer

[Andy Lutomirski]

On Tue, May 14, 2019 at 10:05 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Tue, May 14, 2019 at 06:24:48PM +0200, Alexandre Chartre wrote:
> > On 5/14/19 5:23 PM, Andy Lutomirski wrote:
>
> > > How important is the ability to enable IRQs while running with the KVM
> > > page tables?
> > >
> >
> > I can't say, I would need to check but we probably need IRQs at least for
> > some timers. Sounds like you would really prefer IRQs to be disabled.
> >
>
> I think what amluto is getting at, is:
>
> again:
>         local_irq_disable();
>         switch_to_kvm_mm();
>         /* do very little -- (A) */
>         VMEnter()
>
>                 /* runs as guest */
>
>         /* IRQ happens */
>         WMExit()
>         /* inspect exit raisin */
>         if (/* IRQ pending */) {
>                 switch_from_kvm_mm();
>                 local_irq_restore();
>                 goto again;
>         }
>

What I'm getting at is that running the kernel without mapping the
whole kernel is a horrible, horrible thing to do.  The less code we
can run like that, the better.