spapr/xics: Configure number of servers in KVM

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 <[email protected]>
Message-Id: <157478678846.67101.9660531022460517710[email protected]>
Reviewed-by: Cédric Le Goater <[email protected]>
Signed-off-by: David Gibson <[email protected]>

diff --git a/hw/intc/xics_kvm.c b/hw/intc/xics_kvm.c
index a1f1b7b0d37cd969a2a3f28243eff3bc00e60c93..8d6156578fbc1e39e75c21e958354ec7619af763 100644 (file)
--- 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;