[Qemu-devel] [PATCH] spapr: ensure we have at least one XICS server

[Greg Kurz]

XICS needs to know the upper value for cpu_index as it is used to compute
the number of servers:

    smp_cpus * kvmppc_smt_threads() / smp_threads

When passing -smp cpus=1,threads=9 on a POWER8 host, we end up with:

    1 * 8 / 9 = 0

... which leads to an assertion in both emulated:

Number of servers needs to be greater 0
Aborted (core dumped)

... and in-kernel XICS:

xics_kvm_realize: Assertion `icp->nr_servers' failed.
Aborted (core dumped)

With this patch, we are sure that nr_servers > 0. Passing the same bogus
-smp option then leads to:

qemu-system-ppc64: Cannot support more than 8 threads on PPC with KVM

... which is a lot more explicit than the XICS errors.

Signed-off-by: Greg Kurz <address@hidden>
---
 hw/ppc/spapr.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 35dca77..92916df 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1475,7 +1475,8 @@ static void ppc_spapr_init(MachineState *machine)
 
     /* Set up Interrupt Controller before we create the VCPUs */
     spapr->icp = xics_system_init(machine,
-                                  smp_cpus * kvmppc_smt_threads() / 
smp_threads,
+                                  DIV_ROUND_UP(smp_cpus * kvmppc_smt_threads(),
+                                               smp_threads),
                                   XICS_IRQS);
 
     /* init CPUs */