Re: [PATCH v3 5/8] xen/arm/gic: Allow routing/removing interrupt to running VMs

[Henry Wang <xin.wang2@xxxxxxx>]

Hi Julien,

On 5/21/2024 8:30 PM, Julien Grall wrote:
> Hi,
>
> On 21/05/2024 05:35, Henry Wang wrote:
> > diff --git a/xen/arch/arm/gic-vgic.c b/xen/arch/arm/gic-vgic.c
> > index 56490dbc43..956c11ba13 100644
> > --- a/xen/arch/arm/gic-vgic.c
> > +++ b/xen/arch/arm/gic-vgic.c
> > @@ -439,24 +439,33 @@ int vgic_connect_hw_irq(struct domain *d, 
> > struct vcpu *v, unsigned int virq,
> >         /* We are taking to rank lock to prevent parallel 
> > connections. */
> >       vgic_lock_rank(v_target, rank, flags);
> > +    spin_lock(&v_target->arch.vgic.lock);
> I know this is what Stefano suggested, but v_target would point to the 
> current affinity whereas the interrupt may be pending/active on the 
> "previous" vCPU. So it is a little unclear whether v_target is the 
> correct lock. Do you have more pointer to show this is correct?
No I think you are correct, we have discussed this in the initial 
version of this patch. Sorry.
I followed the way from that discussion to note down the vcpu ID and 
retrieve here, below is the diff, would this make sense to you?
diff --git a/xen/arch/arm/gic-vgic.c b/xen/arch/arm/gic-vgic.c
index 956c11ba13..134ed4e107 100644
--- a/xen/arch/arm/gic-vgic.c
+++ b/xen/arch/arm/gic-vgic.c
@@ -439,7 +439,7 @@ int vgic_connect_hw_irq(struct domain *d, struct 
vcpu *v, unsigned int virq,
     /* We are taking to rank lock to prevent parallel connections. */
     vgic_lock_rank(v_target, rank, flags);
-    spin_lock(&v_target->arch.vgic.lock);
+ spin_lock(&d->vcpu[p->spi_vcpu_id]->arch.vgic.lock);

     if ( connect )
     {
@@ -465,7 +465,7 @@ int vgic_connect_hw_irq(struct domain *d, struct 
vcpu *v, unsigned int virq,
             p->desc = NULL;
     }

-    spin_unlock(&v_target->arch.vgic.lock);
+ spin_unlock(&d->vcpu[p->spi_vcpu_id]->arch.vgic.lock);
     vgic_unlock_rank(v_target, rank, flags);

     return ret;
diff --git a/xen/arch/arm/include/asm/vgic.h 
b/xen/arch/arm/include/asm/vgic.h
index 79b73a0dbb..f4075d3e75 100644
--- a/xen/arch/arm/include/asm/vgic.h
+++ b/xen/arch/arm/include/asm/vgic.h
@@ -85,6 +85,7 @@ struct pending_irq
     uint8_t priority;
     uint8_t lpi_priority;       /* Caches the priority if this is an 
LPI. */
     uint8_t lpi_vcpu_id;        /* The VCPU for an LPI. */
+    uint8_t spi_vcpu_id;        /* The VCPU for an SPI. */
     /* inflight is used to append instances of pending_irq to
      * vgic.inflight_irqs */
     struct list_head inflight;
diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
index c04fc4f83f..e852479f13 100644
--- a/xen/arch/arm/vgic.c
+++ b/xen/arch/arm/vgic.c
@@ -632,6 +632,7 @@ void vgic_inject_irq(struct domain *d, struct vcpu 
*v, unsigned int virq,
     }
     list_add_tail(&n->inflight, &v->arch.vgic.inflight_irqs);
 out:
+    n->spi_vcpu_id = v->vcpu_id;
     spin_unlock_irqrestore(&v->arch.vgic.lock, flags);

     /* we have a new higher priority irq, inject it into the guest */
     vcpu_kick(v);


> Also, while looking at the locking, I noticed that we are not doing 
> anything with GIC_IRQ_GUEST_MIGRATING. In gic_update_one_lr(), we seem 
> to assume that if the flag is set, then p->desc cannot be NULL.
> Can we reach vgic_connect_hw_irq() with the flag set?
I think even from the perspective of making the code extra safe, we 
should also check GIC_IRQ_GUEST_MIGRATING as the LR is allocated for 
this case. I will also add the check of GIC_IRQ_GUEST_MIGRATING here.
> What about the other flags? Is this going to be a concern if we don't 
> reset them?
I don't think so, if I am not mistaken, no LR will be allocated with 
other flags set.
Kind regards,
Henry

> Cheers,