[Xen-devel] [RFC XEN PATCH v3 08/11] xen: arm: vgic: don't fail if IRQ is already connected

[Stewart Hildebrand <stewart.hildebrand@xxxxxxxxxxxxxxx>]

There are some IRQs that happen to have multiple "interrupts = < ... >;"
properties with the same IRQ in the device tree. For example:

interrupts = <0 123 4>,
             <0 123 4>,
             <0 123 4>,
             <0 123 4>,
             <0 123 4>;

In this case it seems that we are invoking vgic_connect_hw_irq multiple
times for the same IRQ.

Rework the checks to allow booting in this scenario.

I have not seen any cases where the pre-existing p->desc is any different from
the new desc, so BUG() out if they're different for now.

Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxxxxxxxxxx>

---
v3: new patch

I tested on Xilinx Zynq UltraScale+ with the old vGIC. I have not fully
tested with CONFIG_NEW_VGIC. This hack only became necessary after
introducing the PPI series, and I'm not entirely sure what the reason
is for that.

I'm also unsure if BUG()ing out is the right thing to do in case of
desc != p->desc, or what conditions would even trigger this? Is this
function exposed to guests?
---
 xen/arch/arm/gic-vgic.c  | 9 +++++++--
 xen/arch/arm/vgic/vgic.c | 4 ++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/gic-vgic.c b/xen/arch/arm/gic-vgic.c
index 2c66a8fa92..5c16e66b32 100644
--- a/xen/arch/arm/gic-vgic.c
+++ b/xen/arch/arm/gic-vgic.c
@@ -460,9 +460,14 @@ int vgic_connect_hw_irq(struct domain *d, struct vcpu *v, 
unsigned int virq,
     if ( connect )
     {
         /* The VIRQ should not be already enabled by the guest */
-        if ( !p->desc &&
-             !test_bit(GIC_IRQ_GUEST_ENABLED, &p->status) )
+        if ( !test_bit(GIC_IRQ_GUEST_ENABLED, &p->status) )
+        {
+            if (p->desc && p->desc != desc)
+            {
+                BUG();
+            }
             p->desc = desc;
+        }
         else
             ret = -EBUSY;
     }
diff --git a/xen/arch/arm/vgic/vgic.c b/xen/arch/arm/vgic/vgic.c
index f0f2ea5021..aa775f7668 100644
--- a/xen/arch/arm/vgic/vgic.c
+++ b/xen/arch/arm/vgic/vgic.c
@@ -882,6 +882,10 @@ int vgic_connect_hw_irq(struct domain *d, struct vcpu 
*vcpu,
             irq->hw = true;
             irq->hwintid = desc->irq;
         }
+        else if ( irq->hw && !irq->enabled && irq->hwintid == desc->irq )
+        {
+            /* The IRQ was already connected. No action is necessary. */
+        }
         else
             ret = -EBUSY;
     }
-- 
2.24.0


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