Re: [PATCH] KVM: prevent spurious exit to userspace during task switch emulation.

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On 04/15/2010 12:28 PM, Gleb Natapov wrote:
kvm_task_switch() never requires userspace exit, so no matter what the
function returns we should not exit to userspace.

Signed-off-by: Gleb Natapov<gleb@xxxxxxxxxx>
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index c773a46..1bd434b 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2254,7 +2254,8 @@ static int task_switch_interception(struct vcpu_svm *svm)
  	     (int_vec == OF_VECTOR || int_vec == BP_VECTOR)))
  		skip_emulated_instruction(&svm->vcpu);

-	return kvm_task_switch(&svm->vcpu, tss_selector, reason);
+	kvm_task_switch(&svm->vcpu, tss_selector, reason);
+	return 1;
  }

  static int cpuid_interception(struct vcpu_svm *svm)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 453f080..3e1607d 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3306,8 +3306,7 @@ static int handle_task_switch(struct kvm_vcpu *vcpu)
  		       type != INTR_TYPE_NMI_INTR))
  		skip_emulated_instruction(vcpu);

-	if (!kvm_task_switch(vcpu, tss_selector, reason))
-		return 0;
+	kvm_task_switch(vcpu, tss_selector, reason);

Ignoring the return seems wrong.  At the very least log errors in dmesg 
(rate-limited).
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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