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

[Andre Przywara <andre.przywara@xxxxxxx>]

Hi,

On 22/05/17 23:15, Stefano Stabellini wrote:
> On Tue, 16 May 2017, Julien Grall wrote:
>> 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.
> 
> right, it should be initialized to INVALID_VCPU_ID

That's right, I fixed that now.

Cheers,
Andre.

>>>      /* inflight is used to append instances of pending_irq to
>>>       * vgic.inflight_irqs */
>>>      struct list_head inflight;
>>>
>>
>> Cheers,
>>
>> -- 
>> Julien Grall
>>

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