Re: [PATCH v5] KVM: VMX: Execute WBINVD to keep data consistency with assigned devices

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Jun 29, 2010 at 04:28:35PM +0300, Avi Kivity wrote:
> On 06/29/2010 04:25 PM, Marcelo Tosatti wrote:
> >
> >>+			smp_call_function_single(vcpu->cpu,
> >>+					wbinvd_ipi, NULL, 1);
> >>+	}
> >>+
> >>  	kvm_x86_ops->vcpu_load(vcpu, cpu);
> >>  	if (unlikely(per_cpu(cpu_tsc_khz, cpu) == 0)) {
> >>  		unsigned long khz = cpufreq_quick_get(cpu);
> >>@@ -3650,6 +3670,21 @@ int emulate_invlpg(struct kvm_vcpu *vcpu, gva_t address)
> >>  	return X86EMUL_CONTINUE;
> >>  }
> >>
> >>+int kvm_emulate_wbinvd(struct kvm_vcpu *vcpu)
> >>+{
> >>+	if (!need_emulate_wbinvd(vcpu))
> >>+		return X86EMUL_CONTINUE;
> >>+
> >>+	if (kvm_x86_ops->has_wbinvd_exit()) {
> >>+		smp_call_function_many(vcpu->arch.wbinvd_dirty_mask,
> >>+				wbinvd_ipi, NULL, 1);
> >work_on_cpu() loop instead of smp_call_function_many(), to avoid executing
> >wbinvd with interrupts disabled.
> 
> Why?  wbinvd is not interruptible.

Right. But still, smp_call_function_many() is going to busy-spin until
the target CPUs finish their work, while work_on_cpu() will schedule.

Also the IPI request has to handled immediately, bypassing the
scheduler.