target-ppc: Force CPU threads count to be a power of 2

PowerPC kernel expects the number of SMT threads in a core to be a power
of 2. Since QEMU doesn't enforce this, it leads to an early guest kernel
crash if invalid threads count is specified.

Prevent this crash and make it a graceful exit from QEMU itself by
validating the user-supplied threads count.

Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/target-ppc/translate_init.c b/target-ppc/translate_init.c
index 3269c3ebe4..5302bdc1b2 100644
--- a/target-ppc/translate_init.c
+++ b/target-ppc/translate_init.c
@@ -7848,6 +7848,12 @@ static void ppc_cpu_realizefn(DeviceState *dev, Error **errp)
                    max_smt, kvm_enabled() ? "KVM" : "TCG");
         return;
     }
+    if (!is_power_of_2(smp_threads)) {
+        error_setg(errp, "Cannot support %d threads on PPC with %s, "
+                   "threads count must be a power of 2.",
+                   smp_threads, kvm_enabled() ? "KVM" : "TCG");
+        return;
+    }
 
     cpu->cpu_dt_id = (cs->cpu_index / smp_threads) * max_smt
         + (cs->cpu_index % smp_threads);