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

["Andreas Färber" <afaerber@suse.de>]

Am 19.03.2014 03:47, schrieb Bharata B Rao:
> On Wed, Mar 05, 2014 at 06:59:29AM -0700, Eric Blake wrote:
>> On 03/05/2014 01:32 AM, Bharata B Rao wrote:
>>> 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
>>
>> Reviewed-by: Eric Blake <eblake@redhat.com>
> 
>> Reviewed-by: Stewart Smith <stewart@linux.vnet.ibm.com>
> 
> Alexander/Andreas,
> 
> Could you take this patch into your tree ?

Thanks for the reminder.

Didn't apply cleanly any more. Applied to my ppc-next with fixups:
https://github.com/afaerber/qemu-cpu/commits/ppc-next

Andreas

diff --cc target-ppc/translate_init.c
index 3269c3e,5628248..0000000
--- a/target-ppc/translate_init.c
+++ b/target-ppc/translate_init.c
@@@ -7848,12 -7987,20 +7848,18 @@@ static void ppc_cpu_realizefn(DeviceSta
                     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);
  #endif

 -    if (kvm_enabled()) {
 -        if (kvmppc_fixup_cpu(cpu) != 0) {
 -            error_setg(errp, "Unable to virtualize selected CPU with
KVM");
 -            return;
 -        }
 -    } else if (tcg_enabled()) {
 +    if (tcg_enabled()) {
          if (ppc_fixup_cpu(cpu) != 0) {
              error_setg(errp, "Unable to emulate selected CPU with TCG");
              return;

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