Re: [Xen-devel] [PATCH v8 11/27] ARM: VGIC: add vcpu_id to struct pending_irq

[Andre Przywara <andre.przywara@xxxxxxx>]

Hi,

On 12/04/17 13:32, Julien Grall wrote:
> Hi Andre,
> 
> On 12/04/17 01:44, 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.
>>
>> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
>> ---
>>  xen/include/asm-arm/vgic.h | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> 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. */
> 
> You likely want a BUILD_BUG_ON in the code to check a vCPU ID will fit
> in lpi_vcpu_id. See what we did in p2m_init.

Ah, MAX_VIRT_CPUS was the name I was looking for (but couldn't find)
when I had the very same idea yesterday ;-)

Thanks for the pointer!

Cheers,
Andre.

> 
>>      /* inflight is used to append instances of pending_irq to
>>       * vgic.inflight_irqs */
>>      struct list_head inflight;
>>

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