Subject: [PATCH] KVM: ARM: vgic: plug irq injection race

From: [email-masked] (Marc Zyngier)
Date: Fri, 14 Mar 2014 14:40:22 +0000

On Fri, Mar 14 2014 at 04:20:52 AM, Christoffer Dall <[email-masked]> wrote:
> On Fri, Feb 14, 2014 at 02:28:06PM +0000, Marc Zyngier wrote:
>> As it stands, nothing prevents userspace from injecting an interrupt
>> before the guest's GIC is actually initialized.
>> 
>> This goes unnoticed so far (as everything is pretty much statically
>> allocated), but ends up exploding in a spectacular way once we switch
>> to a more dynamic allocation (the GIC data structure isn't there yet).
>> 
>> The fix is to test for the "ready" flag in the VGIC distributor before
>> trying to inject the interrupt. Note that in order to avoid breaking
>> userspace, we have to ignore what is essentially an error.
>> 
>> Signed-off-by: Marc Zyngier <[email-masked]>
>> ---
>>  virt/kvm/arm/vgic.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>> 
>> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
>> index be456ce..d40fe61 100644
>> --- a/virt/kvm/arm/vgic.c
>> +++ b/virt/kvm/arm/vgic.c
>> @@ -1386,7 +1386,8 @@ out:
>>  int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int irq_num,
>>  			bool level)
>>  {
>> -	if (vgic_update_irq_state(kvm, cpuid, irq_num, level))
>> +	if (likely(vgic_initialized(kvm)) &&
>
> Do we need a barrier in kvm_vgic_init before setting the
> kvm->arch.vgic.ready to ensure we observe the correctly initialized
> values of the irq_spi_cpu field here?

Ah, I see. Yes, possibly.

>> +	    vgic_update_irq_state(kvm, cpuid, irq_num, level))
>>  		vgic_kick_vcpus(kvm);
>>  
>>  	return 0;
>> -- 
>> 1.8.3.4
>> 
>
> Otherwise looks good, nicely spotted!

I'll respin something early next week.

Cheers,

	M.
-- 
Jazz is not dead. It just smells funny.