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>

1 files changed, 6 insertions, 4 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 35f82f2c66f6..c10135bc0f2f 100644
--- 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);