Re: [PATCH v4 5/6] KVM: arm64: GICv4.1: Restore VLPI pending state to physical side

[Marc Zyngier <maz@xxxxxxxxxx>]

On 2021-03-15 09:11, Shenming Lu wrote:
> On 2021/3/15 16:30, Marc Zyngier wrote:
> > On 2021-03-13 08:38, Shenming Lu wrote:
> > > From: Zenghui Yu <yuzenghui@xxxxxxxxxx>
> > >
> > > When setting the forwarding path of a VLPI (switch to the HW mode),
> > > we can also transfer the pending state from irq->pending_latch to
> > > VPT (especially in migration, the pending states of VLPIs are 
> > > restored
> > > into kvm’s vgic first). And we currently send "INT+VSYNC" to trigger
> > > a VLPI to pending.
> > >
> > > Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
> > > Signed-off-by: Shenming Lu <lushenming@xxxxxxxxxx>
> > > ---
> > >  arch/arm64/kvm/vgic/vgic-v4.c | 18 ++++++++++++++++++
> > >  1 file changed, 18 insertions(+)
> > >
> > > diff --git a/arch/arm64/kvm/vgic/vgic-v4.c 
> > > b/arch/arm64/kvm/vgic/vgic-v4.c
> > > index ac029ba3d337..3b82ab80c2f3 100644
> > > --- a/arch/arm64/kvm/vgic/vgic-v4.c
> > > +++ b/arch/arm64/kvm/vgic/vgic-v4.c
> > > @@ -449,6 +449,24 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, 
> > > int virq,
> > >      irq->host_irq    = virq;
> > >      atomic_inc(&map.vpe->vlpi_count);
> > >
> > > +    /* Transfer pending state */
> > > +    if (irq->pending_latch) {
> > > +        unsigned long flags;
> > > +
> > > +        ret = irq_set_irqchip_state(irq->host_irq,
> > > +                        IRQCHIP_STATE_PENDING,
> > > +                        irq->pending_latch);
> > > +        WARN_RATELIMIT(ret, "IRQ %d", irq->host_irq);
> > > +
> > > +        /*
> > > +         * Clear pending_latch and communicate this state
> > > +         * change via vgic_queue_irq_unlock.
> > > +         */
> > > +        raw_spin_lock_irqsave(&irq->irq_lock, flags);
> > > +        irq->pending_latch = false;
> > > +        vgic_queue_irq_unlock(kvm, irq, flags);
> > > +    }
> > > +
> > >  out:
> > >      mutex_unlock(&its->its_lock);
> > >      return ret;
> >
> > The read side of the pending state isn't locked, but the write side 
> > is.
> > I'd rather you lock the whole sequence for peace of mind.
>
> Did you mean to lock before emitting the mapping request, Or just 
> before reading
> the pending state?

Just before reading the pending state, so that we can't get a concurrent
modification of that state while we make the interrupt pending in the 
VPT
and clearing it in the emulation.

Thanks,

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