Re: [PATCH 6/7] spapr/xive: Configure number of servers in KVM

[Cédric Le Goater]

On 03/10/2019 14:01, Greg Kurz wrote:
> The 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.
> 
> The 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 an hint to the user.
> 
> Signed-off-by: Greg Kurz <address@hidden>

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

> ---
>  hw/intc/spapr_xive_kvm.c |   22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/intc/spapr_xive_kvm.c b/hw/intc/spapr_xive_kvm.c
> index 51b334b676a1..2a3a9ef22b6f 100644
> --- a/hw/intc/spapr_xive_kvm.c
> +++ b/hw/intc/spapr_xive_kvm.c
> @@ -152,7 +152,8 @@ void kvmppc_xive_cpu_synchronize_state(XiveTCTX *tctx, 
> Error **errp)
>  
>  void kvmppc_xive_cpu_connect(XiveTCTX *tctx, Error **errp)
>  {
> -    SpaprXive *xive = SPAPR_MACHINE(qdev_get_machine())->xive;
> +    MachineState *ms = MACHINE(qdev_get_machine());
> +    SpaprXive *xive = SPAPR_MACHINE(ms)->xive;
>      unsigned long vcpu_id;
>      int ret;
>  
> @@ -171,8 +172,15 @@ void kvmppc_xive_cpu_connect(XiveTCTX *tctx, Error 
> **errp)
>      ret = kvm_vcpu_enable_cap(tctx->cs, KVM_CAP_PPC_IRQ_XIVE, 0, xive->fd,
>                                vcpu_id, 0);
>      if (ret < 0) {
> -        error_setg(errp, "XIVE: unable to connect CPU%ld to KVM device: %s",
> +        Error *err = NULL;
> +
> +        error_setg(&err, "XIVE: unable to connect CPU%ld to KVM device: %s",
>                     vcpu_id, strerror(errno));
> +        if (errno == ENOSPC) {
> +            error_append_hint(&local_err, "Try -smp maxcpus=N with N < %u\n",
> +                              ms->smp.max_cpus);
> +        }
> +        error_propagate(errp, err);
>          return;
>      }
>  
> @@ -768,6 +776,16 @@ void kvmppc_xive_connect(SpaprXive *xive, Error **errp)
>          return;
>      }
>  
> +    /* Tell KVM about the # of VCPUs we may have */
> +    if (kvm_device_check_attr(xive->fd, KVM_DEV_XIVE_GRP_CTRL,
> +                              KVM_DEV_XIVE_NR_SERVERS)) {
> +        if (kvm_device_access(xive->fd, KVM_DEV_XIVE_GRP_CTRL,
> +                              KVM_DEV_XIVE_NR_SERVERS, &xive->nr_servers, 
> true,
> +                              &local_err)) {
> +            goto fail;
> +        }
> +    }
> +
>      /*
>       * 1. Source ESB pages - KVM mapping
>       */
>