[PATCH] KVM: Allow building irqbypass.ko as as module when kvm.ko is a module

From: Sean Christopherson
Date: Fri Mar 14 2025 - 22:46:35 EST


Convert HAVE_KVM_IRQ_BYPASS into a tristate so that selecting
IRQ_BYPASS_MANAGER follows KVM={m,y}, i.e. doesn't force irqbypass.ko to
be built-in.

Note, PPC allows building KVM as a module, but selects HAVE_KVM_IRQ_BYPASS
from a boolean Kconfig, i.e. KVM PPC unnecessarily forces irqbpass.ko to
be built-in. But that flaw is a longstanding PPC specific issue.

Fixes: 61df71ee992d ("kvm: move "select IRQ_BYPASS_MANAGER" to common code")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
include/linux/kvm_host.h | 2 +-
virt/kvm/Kconfig | 2 +-
virt/kvm/eventfd.c | 10 +++++-----
3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f34f4cfaa513..be7e1cd516d1 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2382,7 +2382,7 @@ static inline bool kvm_is_visible_memslot(struct kvm_memory_slot *memslot)
struct kvm_vcpu *kvm_get_running_vcpu(void);
struct kvm_vcpu * __percpu *kvm_get_running_vcpus(void);

-#ifdef CONFIG_HAVE_KVM_IRQ_BYPASS
+#if IS_ENABLED(CONFIG_HAVE_KVM_IRQ_BYPASS)
bool kvm_arch_has_irq_bypass(void);
int kvm_arch_irq_bypass_add_producer(struct irq_bypass_consumer *,
struct irq_bypass_producer *);
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 54e959e7d68f..570938f0455c 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -75,7 +75,7 @@ config KVM_COMPAT
depends on KVM && COMPAT && !(S390 || ARM64 || RISCV)

config HAVE_KVM_IRQ_BYPASS
- bool
+ tristate
select IRQ_BYPASS_MANAGER

config HAVE_KVM_VCPU_ASYNC_IOCTL
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 249ba5b72e9b..11e5d1e3f12e 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -149,7 +149,7 @@ irqfd_shutdown(struct work_struct *work)
/*
* It is now safe to release the object's resources
*/
-#ifdef CONFIG_HAVE_KVM_IRQ_BYPASS
+#if IS_ENABLED(CONFIG_HAVE_KVM_IRQ_BYPASS)
irq_bypass_unregister_consumer(&irqfd->consumer);
#endif
eventfd_ctx_put(irqfd->eventfd);
@@ -274,7 +274,7 @@ static void irqfd_update(struct kvm *kvm, struct kvm_kernel_irqfd *irqfd)
write_seqcount_end(&irqfd->irq_entry_sc);
}

-#ifdef CONFIG_HAVE_KVM_IRQ_BYPASS
+#if IS_ENABLED(CONFIG_HAVE_KVM_IRQ_BYPASS)
void __attribute__((weak)) kvm_arch_irq_bypass_stop(
struct irq_bypass_consumer *cons)
{
@@ -424,7 +424,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
if (events & EPOLLIN)
schedule_work(&irqfd->inject);

-#ifdef CONFIG_HAVE_KVM_IRQ_BYPASS
+#if IS_ENABLED(CONFIG_HAVE_KVM_IRQ_BYPASS)
if (kvm_arch_has_irq_bypass()) {
irqfd->consumer.token = (void *)irqfd->eventfd;
irqfd->consumer.add_producer = kvm_arch_irq_bypass_add_producer;
@@ -609,14 +609,14 @@ void kvm_irq_routing_update(struct kvm *kvm)
spin_lock_irq(&kvm->irqfds.lock);

list_for_each_entry(irqfd, &kvm->irqfds.items, list) {
-#ifdef CONFIG_HAVE_KVM_IRQ_BYPASS
+#if IS_ENABLED(CONFIG_HAVE_KVM_IRQ_BYPASS)
/* Under irqfds.lock, so can read irq_entry safely */
struct kvm_kernel_irq_routing_entry old = irqfd->irq_entry;
#endif

irqfd_update(kvm, irqfd);

-#ifdef CONFIG_HAVE_KVM_IRQ_BYPASS
+#if IS_ENABLED(CONFIG_HAVE_KVM_IRQ_BYPASS)
if (irqfd->producer &&
kvm_arch_irqfd_route_changed(&old, &irqfd->irq_entry)) {
int ret = kvm_arch_update_irqfd_routing(

base-commit: ea9bd29a9c0d757b3384ae3e633e6bbaddf00725
--
2.49.0.rc1.451.g8f38331e32-goog