Hi Andreas,
Thanks for the response.
On 07/08/2013 10:15 PM, Andreas Färber wrote:
> Hi,
>
> Am 08.07.2013 17:49, schrieb Prerna Saxena:
>> On 07/08/2013 02:32 PM, Andreas Färber wrote:
>>> -----BEGIN PGP SIGNED MESSAGE-----
>>> Hash: SHA1
>>>
>>> Am 08.07.2013 03:09, schrieb David Gibson:
>>>> On Sat, Jul 06, 2013 at 11:54:15PM +1000, Alexey Kardashevskiy
>>>> wrote:
>>>>> @@ -1342,6 +1346,13 @@ static void
>>>>> ppc_spapr_init(QEMUMachineInitArgs *args)
>>>>> register_savevm_live(NULL, "spapr/htab", -1, 1,
>>>>> &savevm_htab_handlers, spapr);
>>>>>
>>>>> + /* Ensure that cpu_model is correctly reflected for a KVM
>>>>> guest */ + if (kvm_enabled() && !strcmp(cpu_model, "host")) {
>>>>> + asm ("mfpvr %0" + : "=r"(pvr)); +
>>>>> cpu_model = ppc_cpu_alias_by_pvr(pvr);
>>>>
>>>> This needs to be protected by an ifdef CONFIG_KVM or similar. If
>>>> the compiler optimization level is turned down, so that it doesn't
>>>> recognize that the kvm_enabled() is always false, then this could
>>>> attempt to compile the ppc asm instructions on an x86 (or
>>>> whatever) host.
>>>
>>> This hunk can be completely replaced by QOM mechanisms - just didn't
>>> get to replying yet...
>>
>> Sorry I already sent out a v2, and only then saw your message. Could you
>> pls explain how I could use QOM to replace this code block ?
>
> Well, in short the thing is it has not much to do with KVM. The
> KVM-specific host-powerpc64-cpu type is derived from the one you're
> looking for and thus you can use object_class_get_parent() to obtain the
> parent type and look at its name - stripping "-" TYPE_POWERPC_CPU from
> it should be much more efficient but will give you the detailed name
> including revision. I was planning to propose an alternative patch for that.
This is what my patch does :-)
+const char *ppc_cpu_alias_by_pvr(uint32_t pvr)
+{
+ int i;
+ const char *cpu_alias;
+ char *offset, *model;
+
+ cpu_alias = object_class_get_name(OBJECT_CLASS
+ (ppc_cpu_class_by_pvr(pvr)));
+ ....[snip]
>
> Replacing a concrete model name with its simpler alias is a secondary
> issue (separate patch) that is not specific to KVM or -cpu host. Compare
> -cpu POWER8_v1.0 printing .../POWER8_v1.0@0/... presumably.
>
Agree that this is not specific to KVM. That is the reason I have set it
in a separate function, which can be called otherwise as well.
Just to clarify your response, you want the function I coded to be split
into 2 different pieces, to cater to the two specific requirements you
mention ? That can be done, but not sure if it is too much code bloat.
> Further, Alex has already applied a patch of his working around the
> alias table being a rather archaic construct, not intended for frequent
> use. Instead of adding even more functions that iterate it, we should
> turn it into a hashtable for efficient lookup.
>
Can you / Alexander Graf point me to the fix ? I can rework my patch to
consume it ?
> (Note that the cpu_model_str field may contain more than just the model
> name, it is otherwise unused in softmmu and I was therefore preparing a
> patch to ban its use to linux-user solely, so the type name seems the
> most reliable indicator we have and as a bonus no PVR needed for it.)
>
Hmm, maybe obsoleting PVR check is not such a great idea.
I'm not sure if my earlier email clearly outlined the use-case this
patch was attempting to fix. Here is a detailed explanation :
We will still need PVR based lookups for cases such as the one I have
described. As an illustration, consider running in a KVM environment
where QEMU hasnt been started with a specific CPU type via "-CPU
PPC_MODEL". In this case, we will be required to do a PVR_based lookup
only -- to make sure the guest gets initialized with the same CPU as
host. The notion of _same_cpu_model_ can only be built over a PVR check.
Regards,
--
Prerna Saxena
Linux Technology Centre,
IBM Systems and Technology Lab,
Bangalore, India
