[PATCH][Resend] Fix Warnining in arch/x86/kvm/vmx.c

[Subrata Modak]

Hi Avi/Yaniv,

With gcc --version 4.4.1 20090429 (prerelease)

I get the following warning:
arch/x86/kvm/vmx.c: In function ‘vmx_intr_assist’:
arch/x86/kvm/vmx.c:3233: warning: ‘max_irr’ may be used uninitialized in 
this function
arch/x86/kvm/vmx.c:3233: note: ‘max_irr’ was declared here

Investigation found that:

3231 static void update_tpr_threshold(struct kvm_vcpu *vcpu)
3232 {
3233         int max_irr, tpr;
3234 
3235         if (!vm_need_tpr_shadow(vcpu->kvm))
3236                 return;
3237 
3238         if (!kvm_lapic_enabled(vcpu) ||
3239             ((max_irr = kvm_lapic_find_highest_irr(vcpu)) == -1)) {

        (max_irr = kvm_lapic_find_highest_irr(vcpu)) == -1

may not get a chance to evaluate if:

        !kvm_lapic_enabled(vcpu)

evaluates to true (as the expressions are Or-ed).

3240                 vmcs_write32(TPR_THRESHOLD, 0);
3241                 return;
3242         }
3243 
3244         tpr = (kvm_lapic_get_cr8(vcpu) & 0x0f) << 4;
3245         vmcs_write32(TPR_THRESHOLD, (max_irr > tpr) ? tpr >> 4 : max_irr 
>> 4);

Using (max_irr > tpr) and max_irr >> 4, without max_irr getting initialized can
cause trouble.

3246 }

I would like to propose a small fix for this by interchanging the
operands in ||, so that max_irr is initialized in all instances,
and, the warning fades away, without compromising the criteria of
conditional evaluation inside if().

Signed-Off-By: Subrata Modak <subr...@linux.vnet.ibm.com>,
To: Avi Kivity <a...@qumranet.com>
To: Yaniv Kamay  <ya...@qumranet.com>
To: <kvm@vger.kernel.org>
Cc: Balbir Singh <bal...@linux.vnet.ibm.com>
Cc: Sachin P Sant <sach...@linux.vnet.ibm.com>
Subject: [PATCH][Resend] Fix Warnining in arch/x86/kvm/vmx.c
---

--- a/arch/x86/kvm/vmx.c        2009-05-12 15:28:42.000000000 +0530
+++ b/arch/x86/kvm/vmx.c        2009-05-12 15:51:02.000000000 +0530
@@ -3235,8 +3235,8 @@ static void update_tpr_threshold(struct 
        if (!vm_need_tpr_shadow(vcpu->kvm))
                return;
 
-       if (!kvm_lapic_enabled(vcpu) ||
-           ((max_irr = kvm_lapic_find_highest_irr(vcpu)) == -1)) {
+       if (((max_irr = kvm_lapic_find_highest_irr(vcpu)) == -1) ||
+            !kvm_lapic_enabled(vcpu)) {
                vmcs_write32(TPR_THRESHOLD, 0);
                return;
        }

---
Regards--
Subrata

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