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

From: [email-masked] (Eric Auger)
Date: Wed, 10 Dec 2014 13:45:50 +0100

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
> guests reset the devices on boot, but this could cause issues with
> migration and other non-standard startup configurations.
> 
> Signed-off-by: Christoffer Dall <[email-masked]>
> ---
>  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.

Eric
> +
> +	if (vgic_update_irq_pending(kvm, cpuid, irq_num, level))
>  		vgic_kick_vcpus(kvm);
>  
>  	return 0;
>