[RFC PATCH v3 02/19] KVM: x86: inhibit APICv/AVIC when the guest and/or host changes apic id/base from the defaults.

[Maxim Levitsky]

Neither of these settings should be changed by the guest and it is
a burden to support it in the acceleration code, so just inhibit
it instead.

Also add a boolean 'apic_id_changed' to indicate if apic id ever changed.

Signed-off-by: Maxim Levitsky <mlevi...@redhat.com>
---
 arch/x86/include/asm/kvm_host.h |  3 +++
 arch/x86/kvm/lapic.c            | 25 ++++++++++++++++++++++---
 arch/x86/kvm/lapic.h            |  8 ++++++++
 3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 63eae00625bda..636df87542555 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1070,6 +1070,8 @@ enum kvm_apicv_inhibit {
        APICV_INHIBIT_REASON_ABSENT,
        /* AVIC is disabled because SEV doesn't support it */
        APICV_INHIBIT_REASON_SEV,
+       /* APIC ID and/or APIC base was changed by the guest */
+       APICV_INHIBIT_REASON_RO_SETTINGS,
 };
 
 struct kvm_arch {
@@ -1258,6 +1260,7 @@ struct kvm_arch {
        hpa_t   hv_root_tdp;
        spinlock_t hv_root_tdp_lock;
 #endif
+       bool apic_id_changed;
 };
 
 struct kvm_vm_stat {
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 66b0eb0bda94e..8996675b3ef4c 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2038,6 +2038,19 @@ static void apic_manage_nmi_watchdog(struct kvm_lapic 
*apic, u32 lvt0_val)
        }
 }
 
+static void kvm_lapic_check_initial_apic_id(struct kvm_lapic *apic)
+{
+       if (kvm_apic_has_initial_apic_id(apic))
+               return;
+
+       pr_warn_once("APIC ID change is unsupported by KVM");
+
+       kvm_set_apicv_inhibit(apic->vcpu->kvm,
+                       APICV_INHIBIT_REASON_RO_SETTINGS);
+
+       apic->vcpu->kvm->arch.apic_id_changed = true;
+}
+
 static int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
 {
        int ret = 0;
@@ -2046,9 +2059,11 @@ static int kvm_lapic_reg_write(struct kvm_lapic *apic, 
u32 reg, u32 val)
 
        switch (reg) {
        case APIC_ID:           /* Local APIC ID */
-               if (!apic_x2apic_mode(apic))
+               if (!apic_x2apic_mode(apic)) {
+
                        kvm_apic_set_xapic_id(apic, val >> 24);
-               else
+                       kvm_lapic_check_initial_apic_id(apic);
+               } else
                        ret = 1;
                break;
 
@@ -2335,8 +2350,11 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
                             MSR_IA32_APICBASE_BASE;
 
        if ((value & MSR_IA32_APICBASE_ENABLE) &&
-            apic->base_address != APIC_DEFAULT_PHYS_BASE)
+            apic->base_address != APIC_DEFAULT_PHYS_BASE) {
+               kvm_set_apicv_inhibit(apic->vcpu->kvm,
+                               APICV_INHIBIT_REASON_RO_SETTINGS);
                pr_warn_once("APIC base relocation is unsupported by KVM");
+       }
 }
 
 void kvm_apic_update_apicv(struct kvm_vcpu *vcpu)
@@ -2649,6 +2667,7 @@ static int kvm_apic_state_fixup(struct kvm_vcpu *vcpu,
                }
        }
 
+       kvm_lapic_check_initial_apic_id(vcpu->arch.apic);
        return 0;
 }
 
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 4e4f8a22754f9..b9c406d383080 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -252,4 +252,12 @@ static inline u8 kvm_xapic_id(struct kvm_lapic *apic)
        return kvm_lapic_get_reg(apic, APIC_ID) >> 24;
 }
 
+static inline bool kvm_apic_has_initial_apic_id(struct kvm_lapic *apic)
+{
+       if (apic_x2apic_mode(apic))
+               return true;
+
+       return kvm_xapic_id(apic) == apic->vcpu->vcpu_id;
+}
+
 #endif
-- 
2.26.3