Re: [for-5.0 PATCH v2 3/4] spapr/xics: Configure number of servers in KVM

[Cédric Le Goater]

On 26/11/2019 17:46, Greg Kurz wrote:
> The XICS-on-XIVE KVM devices now has an attribute to configure the number
> of interrupt servers. This allows to greatly optimize the usage of the VP
> space in the XIVE HW, and thus to start a lot more VMs.
> 
> Only set this attribute if available in order to support older POWER9 KVM
> and pre-POWER9 XICS KVM devices.
> 
> The XICS-on-XIVE KVM device now reports the exhaustion of VPs upon the
> connection of the first VCPU. Check that in order to have a chance to
> provide a hint to the user.
> `
> Signed-off-by: Greg Kurz <address@hidden>


Reviewed-by: Cédric Le Goater <address@hidden>

> ---
>  hw/intc/xics_kvm.c |   21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/intc/xics_kvm.c b/hw/intc/xics_kvm.c
> index a1f1b7b0d37c..8d6156578fbc 100644
> --- a/hw/intc/xics_kvm.c
> +++ b/hw/intc/xics_kvm.c
> @@ -165,8 +165,15 @@ void icp_kvm_realize(DeviceState *dev, Error **errp)
>  
>      ret = kvm_vcpu_enable_cap(cs, KVM_CAP_IRQ_XICS, 0, kernel_xics_fd, 
> vcpu_id);
>      if (ret < 0) {
> -        error_setg(errp, "Unable to connect CPU%ld to kernel XICS: %s", 
> vcpu_id,
> -                   strerror(errno));
> +        Error *local_err = NULL;
> +
> +        error_setg(&local_err, "Unable to connect CPU%ld to kernel XICS: %s",
> +                   vcpu_id, strerror(errno));
> +        if (errno == ENOSPC) {
> +            error_append_hint(&local_err, "Try -smp maxcpus=N with N < %u\n",
> +                              MACHINE(qdev_get_machine())->smp.max_cpus);
> +        }
> +        error_propagate(errp, local_err);
>          return;
>      }
>      enabled_icp = g_malloc(sizeof(*enabled_icp));
> @@ -399,6 +406,16 @@ int xics_kvm_connect(SpaprInterruptController *intc, 
> uint32_t nr_servers,
>          goto fail;
>      }
>  
> +    /* Tell KVM about the # of VCPUs we may have (POWER9 and newer only) */
> +    if (kvm_device_check_attr(rc, KVM_DEV_XICS_GRP_CTRL,
> +                              KVM_DEV_XICS_NR_SERVERS)) {
> +        if (kvm_device_access(rc, KVM_DEV_XICS_GRP_CTRL,
> +                              KVM_DEV_XICS_NR_SERVERS, &nr_servers, true,
> +                              &local_err)) {
> +            goto fail;
> +        }
> +    }
> +
>      kernel_xics_fd = rc;
>      kvm_kernel_irqchip = true;
>      kvm_msi_via_irqfd_allowed = true;
>