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

From: Glauber Costa
Subject: [Qemu-devel] Re: [PATCH] return default values for apic probe functions.
Date: Fri, 17 Apr 2009 10:40:23 -0300

On Fri, Apr 17, 2009 at 10:22 AM, Glauber Costa <address@hidden> 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"

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

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