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Re: [libvirt] Is seems necessary to pass "migratable=no/yes" to qemu.



On 09/25/2014 02:59 PM, Ján Tomko wrote:
> On 09/25/2014 04:31 AM, zhang bo wrote:
>> On 2014/9/24 19:49, Ján Tomko wrote:
>>> I think the simplest fix for host-passthrough would be to apply the same
>>> filter host-model has.
>>>
>>> But since using invtsc with host-passthrough requires both +invtsc and
>>> migratable=no, so we'd need to either add a 'migratable' option to
>>> host-passthrough (this would skip the filter and add migratable=on), or allow
>>> fine-tuning the features for host-passthrough too.
>>>
>>> Jan
>>>
>>
>>    Additional to the 2 suggestions, will that be OK to remove the codes in qemuProcessVerifyGuestCPU that checks whether the vm->def has
>>    invtsc flag while qemu doesn't?
>>
>> -             if (STREQ(feature->name, "invtsc") &&
>> -                 !cpuHasFeature(guestcpu, feature->name)) {
>> -                 virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
>> -                                _("host doesn't support invariant TSC"));
>> -                 goto cleanup;
>> -             }
> 
> Without this check, the feature would be quietly discarded by QEMU if the host
> kernel or host CPU does not support this feature.
> 
> I think it's better to leave "invtsc" out when we're generating the cpu
> definition for host-passthrough, as we do for host-model.
> 
> Jan
> 
>>
>>    Removing these codes, plus with the solution that "add 'migratable' option to host-passthrough", it seems the problem would
>>    be gone, and invtsc would not be so 'distinctive' in libvirt any more.
>>

I've sent a patch that filters out the flag and also ignores the check for
host-passthrough (to allow guests already saved with the flag to be restored)

https://www.redhat.com/archives/libvir-list/2014-September/msg01680.html

Can you please take a look at it?

Thanks,

Jan

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