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

[Marcelo Tosatti <mtosatti@redhat.com>]

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.

You still need to state explicitly that mpstate should be written back,
in the reset / vmloads paths. 

The advantage i think is that you unify the save/restore code in vcpu
entry/exit paths.

> 
> Jan
> 
> > 
> >> TSC MSR, or the guest debugging state. The reset/vmloading/hw-emulation
> >> code would only declare what kind of write-back it wishes: register
> >> state only, partial (excluding everything that touches continuously
> >> running timers), full. Well, basically the model I suggested for proper
> >> mpstate write-back, just even more generalized.
> >>
> >> Jan
> >>
> >> -- 
> >> Siemens AG, Corporate Technology, CT T DE IT 1
> >> Corporate Competence Center Embedded Linux
>