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KVM: prevent spurious exit to userspace during task switch emulation.

PATCH Superseded Gleb Natapov 2 participants 2 messages Apr 15, 2010

Subsystems (3)
x86 KVM KVM x86

v1 of 2 Superseded Latest is v2 →

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Gleb Natapov

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#0 lore raw

PATCH 1/1 KVM: prevent spurious exit to userspace during task switch emulation.

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 <[email protected]>
arch/x86/kvm/svm.c +2 -1
index c773a46..1bd434b 100644
@@ -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)
arch/x86/kvm/vmx.c +1 -2
index 453f080..3e1607d 100644
@@ -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);
 
 	/* clear all local breakpoint enable flags */
 	vmcs_writel(GUEST_DR7, vmcs_readl(GUEST_DR7) & ~55);

--
Gleb.

#1 lore raw
Quoted 24 lines · Gleb Natapov

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<[email protected]>
arch/x86/kvm/svm.c +2 -1
index c773a46..1bd434b 100644
@@ -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)
arch/x86/kvm/vmx.c +0 -0
index 453f080..3e1607d 100644

arch/x86/kvm/vmx.c static int handle_task_switch(struct kvm_vcpu *vcpu) · line 3311

Quoted 8 lines
arch/x86/kvm/vmx.c +1 -2
@@ -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).

Signature · 2 lines
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.