KVM: x86: Don't update vcpu->arch.pv_eoi.msr_val when a bogus value was...

KVM: x86: Don't update vcpu->arch.pv_eoi.msr_val when a bogus value was written to MSR_KVM_PV_EOI_EN

When kvm_gfn_to_hva_cache_init() call from kvm_lapic_set_pv_eoi() fails,
MSR write to MSR_KVM_PV_EOI_EN results in #GP so it is reasonable to
expect that the value we keep internally in KVM wasn't updated.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20211108152819.12485-3-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/lapic.c

@@ -2857,20 +2857,25 @@ int kvm_lapic_set_pv_eoi(struct kvm_vcpu *vcpu, u64 data, unsigned long len)
 	u64 addr = data & ~KVM_MSR_ENABLED;
 	struct gfn_to_hva_cache *ghc = &vcpu->arch.pv_eoi.data;
 	unsigned long new_len;
+	int ret;
 
 	if (!IS_ALIGNED(addr, 4))
 		return 1;
 
-	vcpu->arch.pv_eoi.msr_val = data;
-	if (!pv_eoi_enabled(vcpu))
-		return 0;
+	if (data & KVM_MSR_ENABLED) {
+		if (addr == ghc->gpa && len <= ghc->len)
+			new_len = ghc->len;
+		else
+			new_len = len;
 
-	if (addr == ghc->gpa && len <= ghc->len)
-		new_len = ghc->len;
-	else
-		new_len = len;
+		ret = kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, addr, new_len);
+		if (ret)
+			return ret;
+	}
+
+	vcpu->arch.pv_eoi.msr_val = data;
 
-	return kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, addr, new_len);
+	return 0;
 }
 
 int kvm_apic_accept_events(struct kvm_vcpu *vcpu)