Re: qemu-kvm requires apic initialized before vcpu main loop

[Jan Kiszka <jan.kiszka@web.de>]

[-- Attachment #1: Type: text/plain, Size: 2165 bytes --]

Gleb Natapov wrote:
> On Wed, Dec 09, 2009 at 09:09:54PM +0100, Jan Kiszka wrote:
>> Gleb Natapov wrote:
>>> On Wed, Dec 09, 2009 at 07:23:38PM +0100, Jan Kiszka wrote:
>>>> Marcelo Tosatti wrote:
>>>>> Otherwise a zero apic base is loaded into KVM, which results
>>>>> in interrupts being lost until a proper apic base with enabled 
>>>>> bit set is loaded.
>>>>>
>>>>> Fixes WinXP migration in qemu-kvm origin/next.
>>>>>
>>>>> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>>>>>
>>>>> diff --git a/hw/apic.c b/hw/apic.c
>>>>> index 627ff98..45a4d2b 100644
>>>>> --- a/hw/apic.c
>>>>> +++ b/hw/apic.c
>>>>> @@ -1131,6 +1131,11 @@ int apic_init(CPUState *env)
>>>>>      vmstate_register(s->idx, &vmstate_apic, s);
>>>>>      qemu_register_reset(apic_reset, s);
>>>>>  
>>>>> +    /* apic_reset must be called before the vcpu threads are initialized and load 
>>>>> +     * registers, in qemu-kvm.
>>>>> +     */
>>>>> +    apic_reset(s);
>>>>> +
>>>>>      local_apics[s->idx] = s;
>>>>>      return 0;
>>>>>  }
>>>> Heals the issue I saw with Win2003 Server as well.
>>>>
>>>> Looks all a bit messy though. Hope we can establish a more regular and
>>>> less fragile model on the midterm. I wonder if it wouldn't be better to
>>>> do write-back of the local APIC state along with the register state on
>>>> vmrun (and only there!). The same would apply to things like mpstate,
>>> Write back of mp state there is a bug and introduce races. Do write back
>>> of the whole APIC state there looks like a recipe for disaster.
>> Please read the full suggestion: We will only write-back if we were
>> going through a reset or vmload before. That removes the ugly kvm hooks
>> from generic code and ensures proper ordering /wrt other write-backs.
>> IMHO, anything else will continue to cause headache like the above to us.
>>
> We can't postpone APIC loading till vmrun. This will race with
> devices/other vcpus sending interrupts to the vcpu. APIC state of all
> vcpus should be up-to-date _before_ any vcpu or main loop starts
> running.

Simple to solve, just add another write-back point: vm_start.

Jan


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 257 bytes --]