On Wed, Apr 27, 2022 at 11:02:57PM +0300, Maxim Levitsky wrote: >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 <mlevitsk@xxxxxxxxxx> >--- > 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, You need to add it to check_apicv_inhibit_reasons as well. > }; > > 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; What's the value of this boolean? No one reads it. > }; > > 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"); It is misleading because changing xAPIC ID is supported by KVM; it just isn't compatible with APICv. Probably this pr_warn_once() should be removed. >+ >+ kvm_set_apicv_inhibit(apic->vcpu->kvm, >+ APICV_INHIBIT_REASON_RO_SETTINGS); The indentation here looks incorrect to me. 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; I suggest warning of x2apic mode: if (WARN_ON_ONCE(apic_x2apic_mode(apic))) Because it is weird that callers care about initial apic id when apic is in x2apic mode.