Re: [patch 1/2] KVM: x86: do not entry guest mode if vcpu is not runnable

Marcelo Tosatti
2008-07-21T16:09:38Z

On Mon, Jul 21, 2008 at 11:38:56AM -0300, Marcelo Tosatti wrote:
> If a vcpu has been offlined, or not initialized at all, signals
> requesting userspace work to be performed will result in KVM attempting
> to re-entry guest mode.
>
> Problem is that the in-kernel irqchip emulation happily executes HALTED
> state vcpu's. This breaks "savevm" on Windows SMP installation (that
> only boots up a single vcpu), for example.
>
> Fix it by blocking halted vcpu's at kvm_arch_vcpu_ioctl_run().
>
> Change the promotion from halted to running to happen in the vcpu
> context. Use the information available in kvm_vcpu_block(), and the
> current mpstate to make the decision:
>
> - If there's an in-kernel timer or irq event the halted->running
> promotion evaluation can be performed, no need for userspace assistance.
>
> - If there's a signal, there's either userspace work to be performed
> in the vcpu's context or irqchip emulation is in userspace.
>
> This has the nice side effect of avoiding userspace exit in case
> of irq injection to a halted vcpu from the iothread.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Thinko: reset the vcpu if SIPI received.

BTW, "INIT"/"SIPI" states are x86/IA64 specific MP protocol information,
aren't they? What are they doing in include/linux/ ?

Index: kvm/arch/x86/kvm/x86.c
===================================================================
--- kvm.orig/arch/x86/kvm/x86.c
+++ kvm/arch/x86/kvm/x86.c
@@ -2521,7 +2521,7 @@ int kvm_emulate_halt(struct kvm_vcpu *vc
up_read(&vcpu->kvm->slots_lock);
ret = kvm_vcpu_block(vcpu);
down_read(&vcpu->kvm->slots_lock);
- if (ret)
+ if (ret || vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED)
return -EINTR;
kvm_vcpu_promote_runnable(vcpu);
return 1;