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

[Zenghui Yu]

Hi Marc,

On 2020/1/15 21:32, Marc Zyngier wrote:
> 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@xxxxxxxxxx>
> > > > ---
> >
> > [...]
> >
> > > > 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)
> > > > ÂÂÂÂÂ return IRQ_HANDLED;
> > > > Â }
> > > > Â +static void vgic_v4_sync_sgi_config(struct its_vpe *vpe, struct 
> > > > vgic_irq *irq)
> > > > +{
> > > > +ÂÂÂ vpe->sgi_config[irq->intid].enabledÂÂÂ = irq->enabled;
> > > > +ÂÂÂ vpe->sgi_config[irq->intid].groupÂÂÂÂ = irq->group;
> > > > +ÂÂÂ vpe->sgi_config[irq->intid].priorityÂÂÂ = irq->priority;
> > > > +}
> > > > +
> > > > +static void vgic_v4_enable_vsgis(struct kvm_vcpu *vcpu)
> > > > +{
> > > > +ÂÂÂ struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
> > > > +ÂÂÂ int i;
> > > > +
> > > > +ÂÂÂ /*
> > > > +ÂÂÂÂ * With GICv4.1, every virtual SGI can be directly injected. So
> > > > +ÂÂÂÂ * let's pretend that they are HW interrupts, tied to a host
> > > > +ÂÂÂÂ * IRQ. The SGI code will do its magic.
> > > > +ÂÂÂÂ */
> > > > +ÂÂÂ for (i = 0; i < VGIC_NR_SGIS; i++) {
> > > > +ÂÂÂÂÂÂÂ struct vgic_irq *irq = vgic_get_irq(vcpu->kvm, vcpu, i);
> > > > +ÂÂÂÂÂÂÂ struct irq_desc *desc;
> > > > +ÂÂÂÂÂÂÂ int ret;
> > > > +
> > > > +ÂÂÂÂÂÂÂ if (irq->hw) {
> > > > +ÂÂÂÂÂÂÂÂÂÂÂ vgic_put_irq(vcpu->kvm, irq);
> > > > +ÂÂÂÂÂÂÂÂÂÂÂ continue;
> > > > +ÂÂÂÂÂÂÂ }
> > > > +
> > > > +ÂÂÂÂÂÂÂ irq->hw = true;
> > > > +ÂÂÂÂÂÂÂ irq->host_irq = irq_find_mapping(vpe->sgi_domain, i);
> > >
> > > I think we need to check whether irq_find_mapping returns 0.
> > >
> > > > +ÂÂÂÂÂÂÂ vgic_v4_sync_sgi_config(vpe, irq);
> > > > +ÂÂÂÂÂÂÂ /*
> > > > +ÂÂÂÂÂÂÂÂ * SGIs are initialised as disabled. Enable them if
> > > > +ÂÂÂÂÂÂÂÂ * required by the rest of the VGIC init code.
> > > > +ÂÂÂÂÂÂÂÂ */
> > > > +ÂÂÂÂÂÂÂ desc = irq_to_desc(irq->host_irq);
> > > > +ÂÂÂÂÂÂÂ ret = irq_domain_activate_irq(irq_desc_get_irq_data(desc),
> > > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ 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.

I haven't had the appropriate HW yet.. Nianyao or Shaokun can help to
test it tomorrow, I think.

> Thanks,
>
>  ÂÂÂÂÂÂÂ M.
>
> [1] 
> https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/commit/?h=irq/gic-v4.1-devel&id=b82c2ee1d3fef66fb85793965c344260f618219d 

Anyway, this looks good to me.


Thanks,
Zenghui