Re: [Xen-devel] [PATCH v9 11/28] ARM: VGIC: add vcpu_id to struct pending_irq

[Julien Grall <julien.grall@xxxxxxx>]

Hi Andre,

On 11/05/17 18:53, Andre Przywara wrote:
> 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>
> ---
>  xen/arch/arm/vgic.c        | 3 +++
>  xen/include/asm-arm/vgic.h | 1 +
>  2 files changed, 4 insertions(+)
>
> diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
> index 27d6b51..97a2cf2 100644
> --- a/xen/arch/arm/vgic.c
> +++ b/xen/arch/arm/vgic.c
> @@ -63,6 +63,9 @@ 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);
> +
>      INIT_LIST_HEAD(&p->inflight);
>      INIT_LIST_HEAD(&p->lr_queue);
>      p->irq = virq;
> diff --git a/xen/include/asm-arm/vgic.h b/xen/include/asm-arm/vgic.h
> index e2111a5..02732db 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. */
Based on the previous patch (#10), I was expecting to see this new field 
initialized in vgic_init_pending_irq.
>      /* inflight is used to append instances of pending_irq to
>       * vgic.inflight_irqs */
>      struct list_head inflight;
Cheers,

--
Julien Grall

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