Re: [PATCH V2 1/8] xen/arm64: increase MAX_VIRT_CPUS to 128 on arm64

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

Hi Chen,

On 23/05/2015 14:52, Chen Baozi wrote:
> From: Chen Baozi <baozich@gmail.com>
>
> GIC-500 supports up to 128 cores in a single SoC. Increase MAX_VIRT_CPUS
> to 128 on arm64.

This series have to be bisectable. Although, this patch will break 
compilation on ARM64 because you increased MAX_VIRT_CPUS without the 
re-distributor region (done in the next patch).

Furthermore, GICv2 is only supporting 8 CPUs. We don't have to allow a 
guest with more than 8 vCPUs when the GICv2 is in use.

Lastly, given that the support of 128 vCPUs will only worked when the 
last patch of this series is applied, I would move this patch at the end.

> Signed-off-by: Chen Baozi <baozich@gmail.com>
> ---
>   xen/arch/arm/vgic-v3.c       | 2 +-
>   xen/include/asm-arm/config.h | 4 ++++
>   2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/vgic-v3.c b/xen/arch/arm/vgic-v3.c
> index 45d54a2..40e1892 100644
> --- a/xen/arch/arm/vgic-v3.c
> +++ b/xen/arch/arm/vgic-v3.c
> @@ -906,7 +906,7 @@ static int vgic_v3_distr_mmio_write(struct vcpu *v, mmio_info_t *info)
>           rank = vgic_rank_offset(v, 64, gicd_reg - GICD_IROUTER,
>                                   DABT_DOUBLE_WORD);
>           if ( rank == NULL ) goto write_ignore;
> -        BUG_ON(v->domain->max_vcpus > 8);
> +        BUG_ON(v->domain->max_vcpus > MAX_VIRT_CPUS);

This check is pointless. max_vcpus will always be inferior or equal to 
MAX_VIRT_CPUS.

>           new_irouter = *r;
>           vgic_lock_rank(v, rank, flags);
>
> diff --git a/xen/include/asm-arm/config.h b/xen/include/asm-arm/config.h
> index 3b23e05..817c216 100644
> --- a/xen/include/asm-arm/config.h
> +++ b/xen/include/asm-arm/config.h
> @@ -47,7 +47,11 @@
>   #define NR_CPUS 128
>   #endif
>
> +#ifdef CONFIG_ARM_64
> +#define MAX_VIRT_CPUS 128
> +#else
>   #define MAX_VIRT_CPUS 8
> +#endif
>
>   #define asmlinkage /* Nothing needed */
>
>

Regards,

-- 
Julien Grall