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

[Julien Grall <julien.grall@arm.com>]

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@arm.com>
> ---
>  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.

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

Cheers,

-- 
Julien Grall

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