Re: [Qemu-arm] [PATCH] KVM: arm/arm64: vgic: Allow more than 256 vcpus for KVM_IRQ_LINE

[Zenghui Yu]

Hi Marc,

On 2019/8/18 22:07, Marc Zyngier wrote:
> While parts of the VGIC support a large number of vcpus (we
> bravely allow up to 512), other parts are more limited.
>
> One of these limits is visible in the KVM_IRQ_LINE ioctl, which
> only allows 256 vcpus to be signalled when using the CPU or PPI
> types. Unfortunately, we've cornered ourselves badly by allocating
> all the bits in the irq field.
>
> Since the irq_type subfield (8 bit wide) is currently only taking
> the values 0, 1 and 2 (and we have been careful not to allow anything
> else), let's reduce this field to only 4 bits, and allocate the
> remaining 4 bits to a vcpu2_index, which acts as a multiplier:
>
>    vcpu_id = 256 * vcpu2_index + vcpu_index
>
> With that, and a new capability (KVM_CAP_ARM_IRQ_LINE_LAYOUT_2)
> allowing this to be discovered, it becomes possible to inject
> PPIs to up to 4096 vcpus. But please just don't.
>
> Reported-by: Zenghui Yu <address@hidden>
> Signed-off-by: Marc Zyngier <address@hidden>
> ---

Reviewed-by: Zenghui Yu <address@hidden>

And tested together with Eric's patches (KVM+QEMU).


Thanks,
zenghui