KVM: x86: Avoid issuing wbinvd twice

Micro optimization to avoid calling wbinvd twice on the CPU that has to
emulate it. As we might be preempted between smp_call_function_many and
the local wbinvd, the cache might be filled again so that real work
could be done uselessly.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 35f82f2..c10135b 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4007,13 +4007,15 @@ int kvm_emulate_wbinvd(struct kvm_vcpu *vcpu)
                return X86EMUL_CONTINUE;
 
        if (kvm_x86_ops->has_wbinvd_exit()) {
-               preempt_disable();
+               int cpu = get_cpu();
+
+               cpumask_set_cpu(cpu, vcpu->arch.wbinvd_dirty_mask);
                smp_call_function_many(vcpu->arch.wbinvd_dirty_mask,
                                wbinvd_ipi, NULL, 1);
-               preempt_enable();
+               put_cpu();
                cpumask_clear(vcpu->arch.wbinvd_dirty_mask);
-       }
-       wbinvd();
+       } else
+               wbinvd();
        return X86EMUL_CONTINUE;
 }
 EXPORT_SYMBOL_GPL(kvm_emulate_wbinvd);