[PATCH 5/5] arm/arm64: KVM: Initialize the vgic on-demand when injecting IRQs

[Christoffer Dall]

On Wed, Dec 10, 2014 at 01:45:50PM +0100, Eric Auger wrote:
> On 12/09/2014 04:44 PM, Christoffer Dall wrote:
> > Userspace assumes that it can wire up IRQ injections after having
> > created all VCPUs and after having created the VGIC, but potentially
> > before starting the first VCPU.  This can currently lead to lost IRQs
> > because the state of that IRQ injection is not stored anywhere and we
> > don't return an error to userspace.
> > 
> > We haven't seen this problem manifest itself yet, 
> Actually we did with VFIO signaling setup before VGIC init!
> presumably because

well, not with code in mainline

> > guests reset the devices on boot, but this could cause issues with
> > migration and other non-standard startup configurations.
> > 
> > Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
> > ---
> >  virt/kvm/arm/vgic.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> > index c98cc6b..feef015 100644
> > --- a/virt/kvm/arm/vgic.c
> > +++ b/virt/kvm/arm/vgic.c
> > @@ -1693,8 +1693,13 @@ out:
> >  int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int irq_num,
> >  			bool level)
> >  {
> > -	if (likely(vgic_ready(kvm)) &&
> > -	    vgic_update_irq_pending(kvm, cpuid, irq_num, level))
> > +	if (unlikely(!vgic_initialized(kvm))) {
> > +		mutex_lock(&kvm->lock);
> > +		vgic_init(kvm);
> > +		mutex_unlock(&kvm->lock);
> > +	}
> I was previously encouraged to test the virtual interrupt controller
> readiness when setting irqfd up(proposal made in
> https://lkml.org/lkml/2014/12/3/601). I guess this becomes useless now,
> correct? Reviewed-by on the whole series.
> 
I think we should move to your userspace explicit init for all
non-legacy userspace and only support gicv3 and vfio/irqfd stuff with
userspace explicitly initializing the vgic.

Thanks for the review!

-Christoffer