Re: [PATCH v3 29/32] KVM: arm64: GICv4.1: Allow SGIs to switch between HW and SW interrupts

[Marc Zyngier <maz@kernel.org>]

On 2020-01-15 03:49, Zenghui Yu wrote:
> Hi,
> 
> On 2020/1/15 10:49, Shaokun Zhang wrote:
>> Hi Marc, [This is from Nianyao]
>> 
>> On 2019/12/24 19:10, Marc Zyngier wrote:
>>> In order to let a guest buy in the new, active-less SGIs, we
>>> need to be able to switch between the two modes.
>>> 
>>> Handle this by stopping all guest activity, transfer the state
>>> from one mode to the other, and resume the guest.
>>> 
>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>> ---
> 
> [...]
> 
>>> diff --git a/virt/kvm/arm/vgic/vgic-v4.c 
>>> b/virt/kvm/arm/vgic/vgic-v4.c
>>> index c2fcde104ea2..063785fd2dc7 100644
>>> --- a/virt/kvm/arm/vgic/vgic-v4.c
>>> +++ b/virt/kvm/arm/vgic/vgic-v4.c
>>> @@ -97,6 +97,102 @@ static irqreturn_t vgic_v4_doorbell_handler(int 
>>> irq, void *info)
>>>   	return IRQ_HANDLED;
>>>   }
>>>   +static void vgic_v4_sync_sgi_config(struct its_vpe *vpe, struct 
>>> vgic_irq *irq)
>>> +{
>>> +	vpe->sgi_config[irq->intid].enabled	= irq->enabled;
>>> +	vpe->sgi_config[irq->intid].group 	= irq->group;
>>> +	vpe->sgi_config[irq->intid].priority	= irq->priority;
>>> +}
>>> +
>>> +static void vgic_v4_enable_vsgis(struct kvm_vcpu *vcpu)
>>> +{
>>> +	struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
>>> +	int i;
>>> +
>>> +	/*
>>> +	 * With GICv4.1, every virtual SGI can be directly injected. So
>>> +	 * let's pretend that they are HW interrupts, tied to a host
>>> +	 * IRQ. The SGI code will do its magic.
>>> +	 */
>>> +	for (i = 0; i < VGIC_NR_SGIS; i++) {
>>> +		struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, i);
>>> +		struct irq_desc *desc;
>>> +		int ret;
>>> +
>>> +		if (irq->hw) {
>>> +			vgic_put_irq(vcpu->kvm, irq);
>>> +			continue;
>>> +		}
>>> +
>>> +		irq->hw = true;
>>> +		irq->host_irq = irq_find_mapping(vpe->sgi_domain, i);
>> 
>> I think we need to check whether irq_find_mapping returns 0.
>> 
>>> +		vgic_v4_sync_sgi_config(vpe, irq);
>>> +		/*
>>> +		 * SGIs are initialised as disabled. Enable them if
>>> +		 * required by the rest of the VGIC init code.
>>> +		 */
>>> +		desc = irq_to_desc(irq->host_irq);
>>> +		ret = irq_domain_activate_irq(irq_desc_get_irq_data(desc),
>>> +					      false);
>> 
>> If irq->host_irq is not valid , in irq_domain_activate_irq, it will 
>> trigger NULL pointer
>> dereference in host kernel.
>> I meet a problem here. When hw support GIC4.1, and host kernel is 
>> started with
>> kvm-arm.vgic_v4_enable=0, starting a virtual machine will trigger NULL 
>> pointer
>> dereference in host.
> 
> I think the thing is that we should _not_ try to configure vSGIs at all
> if kvm-arm.vgic_v4_enable=0 (which indicates we don't allow use of the
> GICv4 of direct injection).
> 
> We currently set kvm_vgic_global_state.has_gicv4_1 to true if HW 
> support
> GICv4.1, regardless whatever the gicv4_enable is (see patch#23 -
> vgic_v3_probe).  I think this is what actually needs fixing.

Yes, my point exactly. I've pushed out a potential fix [1], and I'd be
grateful if you could let me know whether that fixes it for you.

Thanks,

         M.

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/commit/?h=irq/gic-v4.1-devel&id=b82c2ee1d3fef66fb85793965c344260f618219d
-- 
Jazz is not dead. It just smells funny...
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