[PATCH 11/15] KVM: x86: Add CONFIG_KVM_IOAPIC to allow disabling in-kernel I/O APIC
From: Sean Christopherson
Date: Mon May 19 2025 - 19:31:39 EST
Add a Kconfig to allowing building KVM without support for emulating an
I/O APIC, PIC, and PIT, which is desirable for deployments that effectively
don't support a fully in-kernel IRQ chip, i.e. never expect any VMM to
create an in-kernel I/O APIC. E.g. compiling out support eliminates a few
thousand lines of guest-facing code and gives security folks warm fuzzies.
As a bonus, wrapping relevant paths with CONFIG_KVM_IOAPIC #ifdefs makes
it much easier for readers to understand which bits and pieces exist
specific for fully in-kernel IRQ chips.
Opportunistically convert all two in-kernel uses of __KVM_HAVE_IOAPIC to
CONFIG_KVM_IOAPIC, e.g. rather than add a second #ifdef to generate a stub
for kvm_arch_post_irq_routing_update().
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/Kconfig | 10 ++++++++++
arch/x86/kvm/Makefile | 5 +++--
arch/x86/kvm/irq.c | 6 ++++++
arch/x86/kvm/irq_comm.c | 2 ++
arch/x86/kvm/lapic.c | 7 ++++++-
arch/x86/kvm/trace.h | 2 ++
arch/x86/kvm/x86.c | 24 ++++++++++++++++++++----
include/linux/kvm_host.h | 2 +-
include/trace/events/kvm.h | 4 ++--
10 files changed, 54 insertions(+), 10 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ebda93979179..f5ff5174674c 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1374,9 +1374,11 @@ struct kvm_arch {
atomic_t noncoherent_dma_count;
#define __KVM_HAVE_ARCH_ASSIGNED_DEVICE
atomic_t assigned_device_count;
+#ifdef CONFIG_KVM_IOAPIC
struct kvm_pic *vpic;
struct kvm_ioapic *vioapic;
struct kvm_pit *vpit;
+#endif
atomic_t vapics_in_nmi_mode;
struct mutex apic_map_lock;
struct kvm_apic_map __rcu *apic_map;
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 2eeffcec5382..2c86673155c9 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -166,6 +166,16 @@ config KVM_AMD_SEV
Encrypted State (SEV-ES), and Secure Encrypted Virtualization with
Secure Nested Paging (SEV-SNP) technologies on AMD processors.
+config KVM_IOAPIC
+ bool "I/O APIC, PIC, and PIT emulation"
+ default y
+ depends on KVM
+ help
+ Provides support for KVM to emulate an I/O APIC, PIC, and PIT, i.e.
+ for full in-kernel APIC emulation.
+
+ If unsure, say Y.
+
config KVM_SMM
bool "System Management Mode emulation"
default y
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index a5d362c7b504..92c737257789 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -5,12 +5,13 @@ ccflags-$(CONFIG_KVM_WERROR) += -Werror
include $(srctree)/virt/kvm/Makefile.kvm
-kvm-y += x86.o emulate.o i8259.o irq.o lapic.o \
- i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
+kvm-y += x86.o emulate.o irq.o lapic.o \
+ irq_comm.o cpuid.o pmu.o mtrr.o \
debugfs.o mmu/mmu.o mmu/page_track.o \
mmu/spte.o
kvm-$(CONFIG_X86_64) += mmu/tdp_iter.o mmu/tdp_mmu.o
+kvm-$(CONFIG_KVM_IOAPIC) += i8259.o i8254.o ioapic.o
kvm-$(CONFIG_KVM_HYPERV) += hyperv.o
kvm-$(CONFIG_KVM_XEN) += xen.o
kvm-$(CONFIG_KVM_SMM) += smm.o
diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
index b9b9df00ab77..a416ccddde5f 100644
--- a/arch/x86/kvm/irq.c
+++ b/arch/x86/kvm/irq.c
@@ -75,8 +75,10 @@ int kvm_cpu_has_extint(struct kvm_vcpu *v)
if (!kvm_apic_accept_pic_intr(v))
return 0;
+#ifdef CONFIG_KVM_IOAPIC
if (pic_in_kernel(v->kvm))
return v->kvm->arch.vpic->output;
+#endif
WARN_ON_ONCE(!irqchip_split(v->kvm));
return pending_userspace_extint(v);
@@ -135,8 +137,10 @@ int kvm_cpu_get_extint(struct kvm_vcpu *v)
return v->kvm->arch.xen.upcall_vector;
#endif
+#ifdef CONFIG_KVM_IOAPIC
if (pic_in_kernel(v->kvm))
return kvm_pic_read_irq(v->kvm); /* PIC */
+#endif
WARN_ON_ONCE(!irqchip_split(v->kvm));
return get_userspace_extint(v);
@@ -170,7 +174,9 @@ void kvm_inject_pending_timer_irqs(struct kvm_vcpu *vcpu)
void __kvm_migrate_timers(struct kvm_vcpu *vcpu)
{
__kvm_migrate_apic_timer(vcpu);
+#ifdef CONFIG_KVM_IOAPIC
__kvm_migrate_pit_timer(vcpu);
+#endif
kvm_x86_call(migrate_timers)(vcpu);
}
diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
index adef53dc4fef..a4ef150fdd1c 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -208,6 +208,7 @@ int kvm_set_routing_entry(struct kvm *kvm,
* check kvm_arch_can_set_irq_routing() before calling this function.
*/
switch (ue->type) {
+#ifdef CONFIG_KVM_IOAPIC
case KVM_IRQ_ROUTING_IRQCHIP:
if (irqchip_split(kvm))
return -EINVAL;
@@ -231,6 +232,7 @@ int kvm_set_routing_entry(struct kvm *kvm,
}
e->irqchip.irqchip = ue->u.irqchip.irqchip;
break;
+#endif
case KVM_IRQ_ROUTING_MSI:
e->set = kvm_set_msi;
e->msi.address_lo = ue->u.msi.address_lo;
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 73418dc0ebb2..4cf8c1f753d3 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1455,7 +1455,7 @@ static bool kvm_ioapic_handles_vector(struct kvm_lapic *apic, int vector)
static void kvm_ioapic_send_eoi(struct kvm_lapic *apic, int vector)
{
- int trigger_mode;
+ int __maybe_unused trigger_mode;
/* Eoi the ioapic only if the ioapic doesn't own the vector. */
if (!kvm_ioapic_handles_vector(apic, vector))
@@ -1476,12 +1476,14 @@ static void kvm_ioapic_send_eoi(struct kvm_lapic *apic, int vector)
return;
}
+#ifdef CONFIG_KVM_IOAPIC
if (apic_test_vector(vector, apic->regs + APIC_TMR))
trigger_mode = IOAPIC_LEVEL_TRIG;
else
trigger_mode = IOAPIC_EDGE_TRIG;
kvm_ioapic_update_eoi(apic->vcpu, vector, trigger_mode);
+#endif
}
static int apic_set_eoi(struct kvm_lapic *apic)
@@ -3146,8 +3148,11 @@ int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s)
kvm_x86_call(hwapic_isr_update)(vcpu, apic_find_highest_isr(apic));
}
kvm_make_request(KVM_REQ_EVENT, vcpu);
+
+#ifdef CONFIG_KVM_IOAPIC
if (ioapic_in_kernel(vcpu->kvm))
kvm_rtc_eoi_tracking_restore_one(vcpu);
+#endif
vcpu->arch.apic_arb_prio = 0;
diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
index 4ef17990574d..ababdba2c186 100644
--- a/arch/x86/kvm/trace.h
+++ b/arch/x86/kvm/trace.h
@@ -270,6 +270,7 @@ TRACE_EVENT(kvm_cpuid,
{0x6, "SIPI"}, \
{0x7, "ExtINT"}
+#ifdef CONFIG_KVM_IOAPIC
TRACE_EVENT(kvm_ioapic_set_irq,
TP_PROTO(__u64 e, int pin, bool coalesced),
TP_ARGS(e, pin, coalesced),
@@ -314,6 +315,7 @@ TRACE_EVENT(kvm_ioapic_delayed_eoi_inj,
(__entry->e & (1<<15)) ? "level" : "edge",
(__entry->e & (1<<16)) ? "|masked" : "")
);
+#endif
TRACE_EVENT(kvm_msi_set_irq,
TP_PROTO(__u64 address, __u64 data),
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9e2c249d45ca..52eff4919d95 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4630,17 +4630,20 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_EXT_CPUID:
case KVM_CAP_EXT_EMUL_CPUID:
case KVM_CAP_CLOCKSOURCE:
+#ifdef CONFIG_KVM_IOAPIC
case KVM_CAP_PIT:
+ case KVM_CAP_PIT2:
+ case KVM_CAP_PIT_STATE2:
+ case KVM_CAP_REINJECT_CONTROL:
+#endif
case KVM_CAP_NOP_IO_DELAY:
case KVM_CAP_MP_STATE:
case KVM_CAP_SYNC_MMU:
case KVM_CAP_USER_NMI:
- case KVM_CAP_REINJECT_CONTROL:
case KVM_CAP_IRQ_INJECT_STATUS:
case KVM_CAP_IOEVENTFD:
case KVM_CAP_IOEVENTFD_NO_LENGTH:
- case KVM_CAP_PIT2:
- case KVM_CAP_PIT_STATE2:
+
case KVM_CAP_SET_IDENTITY_MAP_ADDR:
case KVM_CAP_VCPU_EVENTS:
#ifdef CONFIG_KVM_HYPERV
@@ -6393,6 +6396,7 @@ static int kvm_vm_ioctl_set_nr_mmu_pages(struct kvm *kvm,
return 0;
}
+#ifdef CONFIG_KVM_IOAPIC
static int kvm_vm_ioctl_get_irqchip(struct kvm *kvm, struct kvm_irqchip *chip)
{
struct kvm_pic *pic = kvm->arch.vpic;
@@ -6521,6 +6525,7 @@ static int kvm_vm_ioctl_reinject(struct kvm *kvm,
return 0;
}
+#endif /* CONFIG_KVM_IOAPIC */
void kvm_arch_sync_dirty_log(struct kvm *kvm, struct kvm_memory_slot *memslot)
{
@@ -7064,9 +7069,11 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
struct kvm *kvm = filp->private_data;
void __user *argp = (void __user *)arg;
int r = -ENOTTY;
+
+#ifdef CONFIG_KVM_IOAPIC
/*
* This union makes it completely explicit to gcc-3.x
- * that these two variables' stack usage should be
+ * that these three variables' stack usage should be
* combined, not added together.
*/
union {
@@ -7074,6 +7081,7 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
struct kvm_pit_state2 ps2;
struct kvm_pit_config pit_config;
} u;
+#endif
switch (ioctl) {
case KVM_SET_TSS_ADDR:
@@ -7097,6 +7105,7 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
case KVM_SET_NR_MMU_PAGES:
r = kvm_vm_ioctl_set_nr_mmu_pages(kvm, arg);
break;
+#ifdef CONFIG_KVM_IOAPIC
case KVM_CREATE_IRQCHIP: {
mutex_lock(&kvm->lock);
@@ -7257,6 +7266,7 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
r = kvm_vm_ioctl_reinject(kvm, &control);
break;
}
+#endif
case KVM_SET_BOOT_CPU_ID:
r = 0;
mutex_lock(&kvm->lock);
@@ -10716,8 +10726,10 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
if (irqchip_split(vcpu->kvm))
kvm_scan_ioapic_routes(vcpu, vcpu->arch.ioapic_handled_vectors);
+#ifdef CONFIG_KVM_IOAPIC
else if (ioapic_in_kernel(vcpu->kvm))
kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
+#endif
if (is_guest_mode(vcpu))
vcpu->arch.load_eoi_exitmap_pending = true;
@@ -12920,7 +12932,9 @@ void kvm_arch_pre_destroy_vm(struct kvm *kvm)
cancel_delayed_work_sync(&kvm->arch.kvmclock_sync_work);
cancel_delayed_work_sync(&kvm->arch.kvmclock_update_work);
+#ifdef CONFIG_KVM_IOAPIC
kvm_free_pit(kvm);
+#endif
kvm_mmu_pre_destroy_vm(kvm);
static_call_cond(kvm_x86_vm_pre_destroy)(kvm);
@@ -12944,8 +12958,10 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
}
kvm_destroy_vcpus(kvm);
kvm_free_msr_filter(srcu_dereference_check(kvm->arch.msr_filter, &kvm->srcu, 1));
+#ifdef CONFIG_KVM_IOAPIC
kvm_pic_destroy(kvm);
kvm_ioapic_destroy(kvm);
+#endif
kvfree(rcu_dereference_check(kvm->arch.apic_map, 1));
kfree(srcu_dereference_check(kvm->arch.pmu_event_filter, &kvm->srcu, 1));
kvm_mmu_uninit_vm(kvm);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 44b439c5fcf4..0e151db44ecd 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1019,7 +1019,7 @@ void kvm_destroy_vcpus(struct kvm *kvm);
void vcpu_load(struct kvm_vcpu *vcpu);
void vcpu_put(struct kvm_vcpu *vcpu);
-#ifdef __KVM_HAVE_IOAPIC
+#ifdef CONFIG_KVM_IOAPIC
void kvm_arch_post_irq_ack_notifier_list_update(struct kvm *kvm);
#else
static inline void kvm_arch_post_irq_ack_notifier_list_update(struct kvm *kvm)
diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h
index 96e581900c8e..1065a81ca57f 100644
--- a/include/trace/events/kvm.h
+++ b/include/trace/events/kvm.h
@@ -84,14 +84,14 @@ TRACE_EVENT(kvm_set_irq,
);
#endif /* defined(CONFIG_HAVE_KVM_IRQCHIP) */
-#if defined(__KVM_HAVE_IOAPIC)
+#ifdef CONFIG_KVM_IOAPIC
#define kvm_irqchips \
{KVM_IRQCHIP_PIC_MASTER, "PIC master"}, \
{KVM_IRQCHIP_PIC_SLAVE, "PIC slave"}, \
{KVM_IRQCHIP_IOAPIC, "IOAPIC"}
-#endif /* defined(__KVM_HAVE_IOAPIC) */
+#endif /* CONFIG_KVM_IOAPIC */
#if defined(CONFIG_HAVE_KVM_IRQCHIP)
--
2.49.0.1101.gccaa498523-goog