KVM: ensure APICv is considered inactive if there is no APIC

kvm_vcpu_apicv_active() returns false if a virtual machine has no in-kernel
local APIC, however kvm_apicv_activated might still be true if there are
no reasons to disable APICv; in fact it is quite likely that there is none
because APICv is inhibited by specific configurations of the local APIC
and those configurations cannot be programmed.  This triggers a WARN:

   WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));

To avoid this, introduce another cause for APICv inhibition, namely the
absence of an in-kernel local APIC.  This cause is enabled by default,
and is dropped by either KVM_CREATE_IRQCHIP or the enabling of
KVM_CAP_IRQCHIP_SPLIT.

Reported-by: Ignat Korchagin <ignat@cloudflare.com>
Fixes: 3abdf8fbb784 ("KVM: x86: Move SVM's APICv sanity check to common x86", 2021-10-22)
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Tested-by: Ignat Korchagin <ignat@cloudflare.com>
Message-Id: <20211130123746.293379-1-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6ac61f85e07b9971c40158d0f7d88cde0e3ba55c..860ed500580cc9af3330ce22b4fa6fec5aac21e8 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1036,6 +1036,7 @@ struct kvm_x86_msr_filter {
 #define APICV_INHIBIT_REASON_PIT_REINJ  4
 #define APICV_INHIBIT_REASON_X2APIC    5
 #define APICV_INHIBIT_REASON_BLOCKIRQ  6
+#define APICV_INHIBIT_REASON_ABSENT    7
 
 struct kvm_arch {
        unsigned long n_used_mmu_pages;

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 9d6066eb7c10edf36a7c4bc2d9524539b5ee6749..8f9af7b7dbbe479fbf914d7c27afdb2d77eb7513 100644 (file)
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -900,6 +900,7 @@ out:
 bool svm_check_apicv_inhibit_reasons(ulong bit)
 {
        ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
+                         BIT(APICV_INHIBIT_REASON_ABSENT) |
                          BIT(APICV_INHIBIT_REASON_HYPERV) |
                          BIT(APICV_INHIBIT_REASON_NESTED) |
                          BIT(APICV_INHIBIT_REASON_IRQWIN) |

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index f90448809690930b91fcd9e9a15f4bb978519613..9453743ce0c410e439ab6074b15c140cc993f03a 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7525,6 +7525,7 @@ static void hardware_unsetup(void)
 static bool vmx_check_apicv_inhibit_reasons(ulong bit)
 {
        ulong supported = BIT(APICV_INHIBIT_REASON_DISABLE) |
+                         BIT(APICV_INHIBIT_REASON_ABSENT) |
                          BIT(APICV_INHIBIT_REASON_HYPERV) |
                          BIT(APICV_INHIBIT_REASON_BLOCKIRQ);
 

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0ee1a039b490996959e137d5b5c53b22712bc36a..e0aa4dd53c7fc98957d0a916df12f37fda9c2f39 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5740,6 +5740,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
                smp_wmb();
                kvm->arch.irqchip_mode = KVM_IRQCHIP_SPLIT;
                kvm->arch.nr_reserved_ioapic_pins = cap->args[0];
+               kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);
                r = 0;
 split_irqchip_unlock:
                mutex_unlock(&kvm->lock);
@@ -6120,6 +6121,7 @@ set_identity_unlock:
                /* Write kvm->irq_routing before enabling irqchip_in_kernel. */
                smp_wmb();
                kvm->arch.irqchip_mode = KVM_IRQCHIP_KERNEL;
+               kvm_request_apicv_update(kvm, true, APICV_INHIBIT_REASON_ABSENT);
        create_irqchip_unlock:
                mutex_unlock(&kvm->lock);
                break;
@@ -8818,10 +8820,9 @@ static void kvm_apicv_init(struct kvm *kvm)
 {
        init_rwsem(&kvm->arch.apicv_update_lock);
 
-       if (enable_apicv)
-               clear_bit(APICV_INHIBIT_REASON_DISABLE,
-                         &kvm->arch.apicv_inhibit_reasons);
-       else
+       set_bit(APICV_INHIBIT_REASON_ABSENT,
+               &kvm->arch.apicv_inhibit_reasons);
+       if (!enable_apicv)
                set_bit(APICV_INHIBIT_REASON_DISABLE,
                        &kvm->arch.apicv_inhibit_reasons);
 }