[Qemu-devel] Re: [PATCH] return default values for apic probe functions.

[Glauber Costa <glommer@gmail.com>]

On Fri, Apr 17, 2009 at 10:22 AM, Glauber Costa <glommer@gmail.com> wrote:
>> Even on sunny days, this collides with QEMU commit #7048. :)
>>
>> Does Intel specify what non-existent MSRs should return, ie. is your
>> version still correct if !s->apicbase means that there is actually no
>> APIC? And does kvm depend on the default base? If so, I would say:
>> provide a patch against upstream.
>
> hummm, I missed this one going in.
> But sadly, your patch also breaks cpu hotplug. Not a segfault anymore, but the
> VM will freeze instead of shutting down, if we ask too. It does not even respond
> to ^C anymore.
>
> By leaving your patch as is, and changing the apic base return to
>
>   return s ? s->apicbase : (0xfee00000 | MSR_IA32_APICBASE_ENABLE);
>
> fixes the issue.
>
After reading the manual, my understanding is that only the flag must
be set. I tried,
and in fact:

   return s ? s->apicbase :  MSR_IA32_APICBASE_ENABLE;

still fixes it.
If it works for you, I believe this is a good solution, and will send
a descriptive patch.
If we ever read the apic as disabled, we will have problems enabling
it again. So for
my test case, kvm should never see a disabled apic.

For yours, you'll still see the apic base address as zero.

what do you think?

-- 
Glauber  Costa.
"Free as in Freedom"
http://glommer.net

"The less confident you are, the more serious you have to act."