[Qemu-devel] [PATCH v2] ppc: Force CPU threads count to be a power of 2.

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

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>
---
Changes in v2: Use is_power_of_2() from QEMU itself instead of depending
on libm.
v1: https://lists.gnu.org/archive/html/qemu-devel/2014-03/msg00660.html
v0: https://lists.gnu.org/archive/html/qemu-devel/2014-03/msg00355.html

 target-ppc/translate_init.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/target-ppc/translate_init.c b/target-ppc/translate_init.c
index 445c360..5628248 100644
--- a/target-ppc/translate_init.c
+++ b/target-ppc/translate_init.c
@@ -7987,6 +7987,12 @@ 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;
+    }
 #endif
 
     if (kvm_enabled()) {
-- 
1.7.11.7