[Xen-devel] [PATCH v12 12/34] ARM: vGIC: add LPI VCPU ID to struct pending_irq

[Andre Przywara <andre.przywara@xxxxxxx>]

The target CPU for an LPI is encoded in the interrupt translation table
entry, so can't be easily derived from just an LPI number (short of
walking *all* tables and find the matching LPI).
To avoid this in case we need to know the VCPU (for the INVALL command,
for instance), put the VCPU ID in the struct pending_irq, so that it is
easily accessible.
We use the remaining 8 bits of padding space for that to avoid enlarging
the size of struct pending_irq. The number of VCPUs is limited to 127
at the moment anyway, which we also confirm with a BUILD_BUG_ON.

Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
Acked-by: Julien Grall <julien.grall@xxxxxxx>
---
 xen/arch/arm/vgic.c        | 4 ++++
 xen/include/asm-arm/vgic.h | 1 +
 2 files changed, 5 insertions(+)

diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
index 204e0d9..c097bd4 100644
--- a/xen/arch/arm/vgic.c
+++ b/xen/arch/arm/vgic.c
@@ -62,10 +62,14 @@ struct vgic_irq_rank *vgic_rank_irq(struct vcpu *v, 
unsigned int irq)
 
 void vgic_init_pending_irq(struct pending_irq *p, unsigned int virq)
 {
+    /* The lpi_vcpu_id field must be big enough to hold a VCPU ID. */
+    BUILD_BUG_ON(BIT(sizeof(p->lpi_vcpu_id) * 8) < MAX_VIRT_CPUS);
+
     memset(p, 0, sizeof(*p));
     INIT_LIST_HEAD(&p->inflight);
     INIT_LIST_HEAD(&p->lr_queue);
     p->irq = virq;
+    p->lpi_vcpu_id = INVALID_VCPU_ID;
 }
 
 static void vgic_rank_init(struct vgic_irq_rank *rank, uint8_t index,
diff --git a/xen/include/asm-arm/vgic.h b/xen/include/asm-arm/vgic.h
index d1fcea1..33b2fb5 100644
--- a/xen/include/asm-arm/vgic.h
+++ b/xen/include/asm-arm/vgic.h
@@ -73,6 +73,7 @@ struct pending_irq
     uint8_t lr;
     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. */
     /* inflight is used to append instances of pending_irq to
      * vgic.inflight_irqs */
     struct list_head inflight;
-- 
2.9.0


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