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

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Dec 09, 2009 at 08:00:41PM +0100, Jan Kiszka wrote:
> Glauber Costa wrote:
> > On Wed, Dec 09, 2009 at 03:46:54PM -0200, 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);
> >> +
> > But by doing this, the system-wide reset will re-reset the apic, possibly losing
> > some other information.
> > 
> > Also, system_reset happens before we signal system_ready (or at least should).
> > This means the vcpus should not be running and producing anything useful yet.
> > So how does it happen, in the first place?
> 
> There is
> 
> 	kvm_arch_load_regs(env);
> 
> before qemu_cond_wait in ap_main_loop. Probably part of the reason. Why
> is it there?

Hum ... see how qemu_kvm_load_lapic depends on kvm_vcpu_inited.

kvm_vcpu_ioctl_set_lapic -> kvm_apic_post_state_restore relies on
proper apicbase set (maybe other reasons too).