KVM: SVM: Update svm->ldr_reg cache even if LDR is "bad"

Update SVM's cache of the LDR even if the new value is "bad".  Leaving
stale information in the cache can result in KVM missing updates and/or
invalidating the wrong entry, e.g. if avic_invalidate_logical_id_entry()
is triggered after a different vCPU has "claimed" the old LDR.

Fixes: 18f40c5 ("svm: Add VMEXIT handlers for AVIC")
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230106011306.85230-27-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/avic.c

@@ -539,23 +539,21 @@ static u32 *avic_get_logical_id_entry(struct kvm_vcpu *vcpu, u32 ldr, bool flat)
 	return &logical_apic_id_table[index];
 }
 
-static int avic_ldr_write(struct kvm_vcpu *vcpu, u8 g_physical_id, u32 ldr)
+static void avic_ldr_write(struct kvm_vcpu *vcpu, u8 g_physical_id, u32 ldr)
 {
 	bool flat;
 	u32 *entry, new_entry;
 
 	flat = kvm_lapic_get_reg(vcpu->arch.apic, APIC_DFR) == APIC_DFR_FLAT;
 	entry = avic_get_logical_id_entry(vcpu, ldr, flat);
 	if (!entry)
-		return -EINVAL;
+		return;
 
 	new_entry = READ_ONCE(*entry);
 	new_entry &= ~AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK;
 	new_entry |= (g_physical_id & AVIC_LOGICAL_ID_ENTRY_GUEST_PHYSICAL_ID_MASK);
 	new_entry |= AVIC_LOGICAL_ID_ENTRY_VALID_MASK;
 	WRITE_ONCE(*entry, new_entry);
-
-	return 0;
 }
 
 static void avic_invalidate_logical_id_entry(struct kvm_vcpu *vcpu)
@@ -575,7 +573,6 @@ static void avic_invalidate_logical_id_entry(struct kvm_vcpu *vcpu)
 
 static void 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 id = kvm_xapic_id(vcpu->arch.apic);
@@ -589,11 +586,8 @@ static void avic_handle_ldr_update(struct kvm_vcpu *vcpu)
 
 	avic_invalidate_logical_id_entry(vcpu);
 
-	if (ldr)
-		ret = avic_ldr_write(vcpu, id, ldr);
-
-	if (!ret)
-		svm->ldr_reg = ldr;
+	svm->ldr_reg = ldr;
+	avic_ldr_write(vcpu, id, ldr);
 }
 
 static void avic_handle_dfr_update(struct kvm_vcpu *vcpu)