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KVM: SVM: Fix potential wrong physical id in avic_handle_ldr_update

PATCH linmiaohe 2 participants 2 messages Oct 17, 2019 KVM

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#0 lore raw
Quoted 3 lines · Vitaly Kuznetsov
Quoted 3 lines

Guest physical APIC ID may not equal to vcpu->vcpu_id in some case. We may set the wrong physical id in avic_handle_ldr_update as we always use vcpu->vcpu_id.

Hi, Vitaly, thanks for your reply.
Do you think there may be a wrong physical id in avic_handle_ldr_update too ?

Quoted 11 lines

Review static int avic_handle_ldr_update(struct kvm_vcpu *vcpu) · line 4595

Quoted 7 lines
(quoted diff) +2 -0
@@ -4591,6 +4591,8 @@ static int avic_handle_ldr_update(struct kvm_vcpu *vcpu)
 	int ret = 0;
 	struct vcpu_svm *svm = to_svm(vcpu);
 	u32 ldr = kvm_lapic_get_reg(vcpu->arch.apic, APIC_LDR);
+	u32 apic_id_reg = kvm_lapic_get_reg(vcpu->arch.apic, APIC_ID);
+	u32 id = (apic_id_reg >> 24) & 0xff;

If we reach here than we're guaranteed to be in xAPIC mode, right? Could you maybe export and use kvm_xapic_id() here then (and in avic_handle_apic_id_update() too)?

I think we're guaranteed to be in xAPIC mode when we reach here. I would have a try to export and use use kvm_xapic_id here and in avic_handle_apic_id_update too.
Thanks for your suggestion.

Have a nice day.
Best wishes.

#1 lore raw
Quoted 9 lines · linmiaohe
Quoted 3 lines · Vitaly Kuznetsov
Quoted 3 lines

Guest physical APIC ID may not equal to vcpu->vcpu_id in some case. We may set the wrong physical id in avic_handle_ldr_update as we always use vcpu->vcpu_id.

Hi, Vitaly, thanks for your reply.
Do you think there may be a wrong physical id in
avic_handle_ldr_update too ?

Honestly I'm not sure, however, as we need to put physical id to LDR we'd rather get it from LAPIC then assume that it's == vcpu_id so I think your patch makes sense even if it fixes a theoretical issue.

But I may be missing something important about AVIC.

Quoted 19 lines
Quoted 12 lines

Review static int avic_handle_ldr_update(struct kvm_vcpu *vcpu) · line 4595

Quoted 8 lines
(quoted diff) +2 -0
@@ -4591,6 +4591,8 @@ static int avic_handle_ldr_update(struct kvm_vcpu *vcpu)
 	int ret = 0;
 	struct vcpu_svm *svm = to_svm(vcpu);
 	u32 ldr = kvm_lapic_get_reg(vcpu->arch.apic, APIC_LDR);
+	u32 apic_id_reg = kvm_lapic_get_reg(vcpu->arch.apic, APIC_ID);
+	u32 id = (apic_id_reg >> 24) & 0xff;

If we reach here than we're guaranteed to be in xAPIC mode, right? Could you maybe export and use kvm_xapic_id() here then (and in avic_handle_apic_id_update() too)?

I think we're guaranteed to be in xAPIC mode when we reach here. I would have a try to export and use use kvm_xapic_id here and in avic_handle_apic_id_update too.
Thanks for your suggestion.

Have a nice day.
Best wishes.

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Vitaly